Thermo Scientific 9616BNWP Instruction Manual

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Analyze •Detect•Measure •Control

™

Orion 94-16 Orion 96-16 ionplus

Orion Silver/Sulfide

Electrode

INSTRUCTION MANUAL

Page 2

AQUAfast, Cahn, EZ Flash, Ionalyzer, ionplus, KNIpHE, No Cal, ORION, perpHect, PerpHecT, PerpHecTion, pHISA, pHix, pHuture, Pure Water, Sage, Sensing the Future, SensorLink, ROSS Ultra, Sure-Flow, TEA Analyzer, Titrator PLUS, TURBO2 and Wine Master are registered trademarks of Thermo Electron Corporation.

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Guaranteed Success and The Technical Edge are service marks of Thermo.

PerpHecT meters are protected by U.S. patent 6,168,707.

PerpHecT ROSS are protected by U.S. patent 6,168,707.

ORION Series A meters and 900A printer are protected by U.S. patents 5,108,578, 5,198,093 and German patents D334,208 and D346,753.

Sure-Flow electrodes are protected by European Patent 278,979 and Canadian Patent 1,286,720.

ionplus electrodes and Optimum Results solutions are protected by US Patent 5,830,338.

ROSS Ultra electrodes have patents pending.

ORION ORP Standard is protected by US Patent 6,350,367.

ORION Series A conductivity meters are protected by US Patent 5,872,454.

The specifications, descriptions, drawings, ordering information and part numbers within this document are subject to change without notice.

This publication supersedes all previous publications on this subject.

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TABLE OF CONTENTS

General Information 1

Introduction 1 Required Equipment 2 Required Solutions 3

Before Using The Electrode 6

Electrode Preparation 6 Checking Electrode Operation (Slope) 9

Helpful Information 10

Units of Measurement 10 Sample Requirements 10 GLP Measuring Hints 11

Choosing the Right Measuring Technique 13 Silver Measurement Procedures 15

Direct Measurement 16 Low-Level Measurements 19 Known Addition 23 Low-Level Chloride Titration 30 Low-Level Cyanide Indicator Method 32

Sulfide Measurement Procedures 36

Direct Measurement 36 Analate Subtraction Measurements 40 Sulfide Titration 44

Electrode Storage 46 Electrode Maintenance 47 Troubleshooting 49

Troubleshooting Checklist 49 Troubleshooting Guide 53

Electrode Characteristics 56

Electrode Response 56 Reproducibility 56 Temperature Effects 57 Interferences 58 pH Effects 59 Complexation 59 Theory of Operation 60

Warranty 62 Ordering Information 66 Specifications 67

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GENERAL INFORMATION

Introduction

The Orion 94-16 Silver/Sulfide Half-Cell Electrode and Orion 96-16 Sure-Flow

™

Combination Silver/Sulfide Electrode measure silver and sulfide ions in aqueous solutions quickly, simply, accurately, and economically. Because of the extreme insolubility of silver sulfide, the two ions are virtually never present in solution together. This electrode also performs low-level cyanide and halide titrations.

The Orion 96-16 offers additional benefits from the Sure-Flow Combination reference design. With this electrode, a separate reference electrode is unnecessary, making it convenient to use with small sample volumes. The free-flowing liquid junction assures stable, drift-free potentials. When measuring dirty samples which would clog conventional electrode junctions, the Sure-Flow junction can be opened and flushed clean simply by pressing the cap. The Orion 900200 Double Junction Reference electrode, when used with the 9416 Silver/Sulfide Half-Cell Electrode, also offers the benefits of the Sure-Flow junction design.

General analytical procedures, required solutions, electrode characteristics, and electrode theory are discussed in this manual. Operator instructions for Orion meters are given in the meter instruction manual.

Thermo Electron Corporation’s The Technical Edge for Customer Service and Support for Orion Products can be consulted for assistance and troubleshooting advice. Please refer to Troubleshooting for information on contacting Thermo Electron.

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Required Equipment

Meter – The easiest to use are direct concentration readout specific

ion meters (ISE meters), such as Orion EA 940, 920A, 720A, 710A, or 290A. If unavailable, a pH/mV meter with readability to 0.1 mV, such as Orion 420A, 520A, or 525A is recommended.

Reference Electrode Orion

For use with Orion 94-16:

Orion 90-02 Double Junction 900200 Reference Electrode, includes:

Inner Chamber Filling Solution 900002 Outer Chamber Filling Solution 900003

For use with Orion 96-16:

The 96-16 Combination n/a Silver/Sulfide Electrode does not require a separate reference electrode.

Magnetic Stirrer, Stir Bars – Recommended for laboratory measurements.

Graph Paper – 4 cycle semi-logarithmic paper for preparing calibration curves (for use with pH/mV laboratory meters).

Plastic Labware – For low-level silver measurements. Polishing Strips – Orion 948201. To clean the silver/sulfide

sensing element.

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Required Solutions

Distilled or Deionized Water – To prepare all solutions and

standards. Water to prepare sulfide standards should also be deaerated.

Reference Filling Solution Orion

Optimum Results

™

B 900062 (for 96-16 Combination Silver/Sulfide Electrode)

Inner Chamber Filling Solution 900002 (for use with 90-02 Reference Electrode)

Outer Chamber Filling Solution 900003 (for use with 90-02 Reference Electrode)

Silver Solutions Orion Standard solution Customer

0.1 M or 1000 ppm as silver Prepared

(see below)

Low-level Chloride Titrant Customer

2.82 x 10

-3

M AgNO

Prepared (see below)

Ionic Strength Adjustor (ISA): 940011 To adjust ionic strength of samples and standards, 5M NaNO

Sulfide Solutions Orion Sulfide Anti-Oxidant 941609

Buffer (SAOB ll) Reagent Pack

Lead Perchlorate Solution (0.1M) 948206

For titration of sulfide standard solutions

Sulfide Standard: Customer 100 ppm as S

Prepared (see below)

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Customer Prepared Solutions Silver Stock Standard Solutions

Required Chemicals:

Silver Nitrate, Reagent Grade, pulverized and dried in oven at 150 °C for one hour.

Distilled Water

Preparation:

0.1 M AgNO

solution:

dry pulverized, reagent grade silver nitrate at 150 °C for one hour. In a 1-liter flask, place 16.99 g of the dried silver nitrate. Dissolve the solid, and dilute to volume with distilled water. Store in an opaque bottle in a dark place.

1000 ppm silver solution:

weigh out 1.57 g of reagent grade silver nitrate, dried as above, in a 1-liter volumetric flask. Dissolve and dilute to volume with distilled water. Store in an opaque bottle in a dark place.

Low-level Chloride Titrant:

2.82 x 10

-3

M AgNO3(equivalent to 100 ppm chloride). For titrations of low-level chloride. Dry reagent grade silver nitrate as directed above. Place 0.479 g dried silver nitrate in a 1 liter volumetric flask. Dissolve and dilute to volume with distilled water. Store in an opaque bottle.

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Customer Prepared Solutions Sulfide Standard Solutions

Required Chemicals:

Sodium Sulfide, reagent grade SAOB II, Orion 941609 Lead Perchlorate, Orion 948206 Distilled, deaerated water.

NOTE: Water must be deaerated to prevent oxidation of sulfide.

Preparation:

Prepare a stock solution of saturated sodium sulfide by dissolving approximately 100 g of reagent-grade Na

S•9H2O in 100 mL distilled, deaerated water. Shake well and let stand overnight. Store in a tightly stoppered bottle in a hood.

Prepare a sulfide standard weekly by pipetting 10 mL of the stock solution into a l liter volumetric flask. Add 500 mL SAOB II and dilute to volume with distilled, deaerated water. Determine the exact concentration, C, by titrating 10 mL of the standard with 0.1 M lead perchlorate, using the electrode(s) as the end point indicator, and calculate:

C= 3206 (V

t/Vs

)

where: C= concentration as ppm sulfide

Vt = volume of titrant at end point Vs = volume of standard (10 mL)

Prepare other standards daily by serial dilution of the weekly standard. To do a ten-fold dilution, pipet 10 mL of the standard into a 100 mL volumetric flask, add 45 mL SAOB II and dilute to volume with distilled, deaerated water.

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BEFORE USING THE ELECTRODE

Electrode Preparation

Orion 94-16 – Silver/Sulfide Half-Cell Electrode

Remove the rubber cap covering the electrode tip.

Orion 9002 – Double Junction Reference Electrode

Fill this reference electrode according to the instructions in the reference electrode instruction manual. Fill the inner chamber with Orion 900002 Filling Solution. Fill the outer chamber with Orion 900003 Filling Solution.

Add filling solution each day before using the electrode. The filling solution level should be at least one inch above the level of sample in the beaker to ensure a proper flow rate. If the filling solution is less than one inch above the sample solution level, electrode potentials may be erratic.

Orion 96-16 – Sure-Flow Combination Silver/Sulfide Electrode

Orion offers a line of filling solutions designed specifically for your application. Chose the Optimum Results

™

filling solution specially formulated for your measuring requirements. See Temperature Effects for a discussion on the benefits of Optimum Results solutions. See Table 1.

Optimum Results B (Orion 900062) supplied with this electrode is designed to minimize junction potentials and silver/sulfide ion contamination of the sample and can be used for most silver/sulfide measurements.

Optimum Results C (Orion 900067) is recommended for precise silver measurements, providing optimum temperature and time response.

Optimum Results A (Orion 900061) is recommended when precise sulfide measurements, providing optimum temperature and time response.

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Table 1 Choosing the correct filling solution for 96-16 Sure-Flow Combination Silver/Sulfide Electrode

Description Orion Purpose

Optimum Results A 900061 Sulfide measurements

Variable sample

temperatures

Optimum Results B 900062 Titration

Measurement of both

and S

Constant sample

temperature

Low-level silver

measurement

Cyanide indicator method

Optimum Results C 900067 Silver measurements

Variable sample

temperatures

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The 96-16 Silver/Sulfide Sure-Flow Combination Electrode is shipped without filling solution in the reference chamber. To fill from the flip-spout bottle:

1. Lift the spout to a vertical position.

2. Insert the spout into the fill hole in the outer sleeve and add a

small amount of filling solution to the chamber. Tip the electrode to moisten the O-ring at the top and return electrode to a vertical position.

3. Holding the electrode by the barrel with one hand, use the thumb

to push down on the electrode cap, allowing a few drops of filling solution to drain and wet the inner cone.

4. Release sleeve. If sleeve does not return to its original position

immediately, check to see if the O-ring is moist enough and repeat steps 2 - 4 until the sleeve has returned to original position. Add filling solution up to the fill hole.

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Checking Electrode Operation (Slope)

This procedure measures electrode slope. Slope is defined as the change in millivolts observed with every ten-fold change in concentration. Obtaining the slope value provides the best means for checking electrode performance.

These are general instructions that can be used with most meters to check electrode operation. See individual meter instruction manuals for more specific information.

1. If electrode(s) have been stored dry, prepare the electrode(s) as

described in Electrode Preparation.

2. Connect the electrode(s) to the meter as described in the meter

instruction manual. Non-Orion meters may require special adapters. Consult your meter instruction manual.

3. For Silver:

Place 100 mL distilled water into a 150 mL beaker. Add 2 mL ISA, (Orion 940011). Stir thoroughly. Use 0.1 M or 1000 ppm silver standard in the following steps.

For Sulfide:

Place 50 mL distilled water into a 150 mL beaker. Add 50 mL SAOB II (Orion 941609). Stir thoroughly. Use 100 ppm sulfide standard in the following steps.

4. Set the meter to the mV mode.

5. Rinse electrode(s) with distilled water, blot dry, and place in the

solution prepared in Step 3 above.

6. Select the appropriate standard. Pipet 1 mL of the standard into

the beaker. Stir thoroughly. When a stable reading is displayed, record the electrode potential in millivolts.

7. Pipet 10 mL of the same standard into the same beaker. Stir

thoroughly. When a stable reading is displayed record the electrode potential in millivolts.

8. The difference between the first and second potential reading

is defined as the slope of the electrode. The difference should be in the range of (+) 54-60 mV/decade (silver) or (-) 25-30 mV/decade (sulfide) when the solution temperature is between 20 and 25 °C. If the slope is not within the appropriate range refer to the Troubleshooting section.

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HELPFUL INFORMATION

Units of Measurement

Silver or sulfide ions can be measured in units of moles per liter, parts per million, or any other convenient unit (see Table 2).

Table 2 Concentration Unit Conversion Factors

For silver: troy oz. Moles/Liter g/L ppm Ag

per gallon

1 107.9 107900 13.128 1 x 10

-3

1.08 x 10

-1

107.9 1.31 x 10

-2

9.27 x 10

-3

1 1000 1.22 x 10

-1

9.27 x 10

-6

1.0 x 10

-3

1 1.22 x 10

-4

7.62 x 10

-2

8.22 8216.9 1

For sulfide: Moles/Liter g/L ppm S

Normality

1 32.06 32060 2.00 1 x 10

-3

3.21x10

-2

32.06 2.0 x 10

-3

3.12 x 10

-2

1 1000 6.24 x 10

-2

3.12 x 10

-5

1.0 x 10

-3

1 6.24 x 10

-5

0.5 16.03 16030 1

Sample Requirements

The epoxy electrode body is resistant to attack by inorganic solutions. The electrode may be used intermittently in solutions containing methanol or ethanol. Consult The Technical Edge for use of the electrode in other organic solvents (see Assistance).

Samples and standards should be at the same temperature. Temperature must be less than 100 °C.

Silver samples must be below pH 8 to avoid reaction with hydroxide ion. Acidify silver samples with 1 M HNO

if necessary.

Sulfide samples must be buffered to pH above 12 with SAOB II so that HS

and H2S are converted to S2-.

Dissolved mercury compounds must be absent from silver samples. Because of the insolubility of HgS and Hg

S, no dissolved mercury

ions will be present in sulfide samples.

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GLP Measuring Hints

See Figure 1. – Stir all standards and samples at a uniform rate during

measurement. Magnetic stirrers may generate sufficient heat to change solution temperature. Place a piece of insulating material such as cork, cardboard, or Styrofoam between the stirrer

and sample beaker. – Prepare fresh working standards for calibration daily. – Always rinse electrode(s) with distilled water between

measurements. Shake after rinsing to prevent solution

carryover. Blot dry. – Allow all standards and samples to come to the same

temperature for precise measurement. _ The 90-02 reference electrode (when used with the 94-16

Silver/Sulfide Half-Cell Electrode) should be submerged to the

same depth as the silver/sulfide electrode. _ Concentrated samples (> 1 M silver or sulfide) should be diluted

before measurement. – After immersion in solution, check electrode(s) for any air

bubbles on the sensing element and remove by gently tapping

the electrode(s). – For high ionic strength samples, prepare standards with

composition similar to that of the sample.

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1. Filling hole should be uncovered (90-02 or 96-16)

2. Fresh standard

3. Stir all samples and standards

4. Filling solution level must be higher than sample level

5. Reference junction must be immersed

6. Place insulation between stirrer and beaker

5 6

Figure 1 GLP Measuring Hints

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CHOOSING THE RIGHT MEASURING TECHNIQUE

A variety of analytical techniques are available to the analyst. Direct Measurement is a simple procedure for measuring a large

number of samples. Only one meter reading is required for each sample. Calibration is performed in a series of standards. The concentration of the samples is determined by comparison to the standards. ISA or SAOB II is added to all solutions to ensure that samples and standards have similar ionic strength, proper pH, and to reduce the effect of interfering ions.

Low-Level Measurement is a similar method to Direct Measurement. This method is recommended when the expected sample concentration is less than 0.5 ppm or 4.6 x 10

-6

M Ag+or

0.32 ppm or 1 x 10-5M S2-. A minimum three point calibration is recommended to compensate for the electrode’s non-linear response at these concentrations. A special procedure describes the best means of preparing low-level calibration standards.

Known Addition is a useful method for measuring samples, since calibration is not required. This method is recommended when measuring only a few samples, or when samples have a high (> 0.1 M) ionic strength, or a complicated background matrix. Refer to Theory of Operation for explanation of these effects. The electrodes are immersed in the sample solution and an aliquot of a standard solution containing the measured species is added to the sample. From the change in potential before and after the addition, the original sample concentration is determined. As in direct calibration, any convenient concentration unit can be used.

Analate Subtraction is also a useful method for measuring samples, since calibration is not required. The electrodes are immersed in a reagent solution that contains a species that the electrode senses, and that reacts with the samples. It is useful when sample size is small, for samples for which a stable standard is difficult to prepare, and for viscous or very concentrated samples. The method is not suited for very dilute samples. It is also necessary to know the stoichiometric ratio between standard and sample.

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Titrations are quantitative analytical techniques for measuring the concentration of a species by incremental addition of a reagent (titrant) that reacts with the sample species. Sensing electrodes can be used for determination of the titration endpoint. Ionselective electrodes are useful as endpoint detectors, because they are unaffected by sample color or turbidity. Titrations are approximately 10 times more precise than direct calibration, but are more time-consuming. For sulfide measurements, titrations produce an extremely sharp endpoint, even at low levels of sulfide. Titration is the recommended measurement method for sulfide samples.

Indicator Titration Methods are useful for measuring ionic species where an ion-specific electrode does not exist. With these methods the electrodes sense a reagent species that has been added to the sample before titration. A procedure for measuring low levels of cyanide ion down to 0.03 ppm, using the silver electrode, is described in the Low-Level Cyanide Indicator Method.

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SILVER MEASUREMENT PROCEDURES

Direct Measurement

The following direct measurement procedures are recommended for “high-level” measurements. All samples must be in the electrode’s linear range, greater than 0.5 ppm or 4.6 x 10

-6

M Ag+. A two point calibration is sufficient, though more points can be used if desired. With ISE meters, such as the Orion 920A, 720A, 710A, or 290A, sample concentrations can be read directly from the meter. Refer to the meter instruction manual for calibration details. When using a mV meter, a calibration curve can be prepared on semilogarithmic graph paper, or a linear regression (against logarithmic concentration values) can be performed at the user’s discretion using a spreadsheet or graphing program.

Measuring Hints

– Standard concentrations should bracket the expected

sample concentrations. – Always add 2 mL ISA per 100 mL of silver standard or sample. – For high ionic strength samples, having an ionic strength of 0.1

M or greater, prepare standards with a composition similar to

that of the samples, or measure the samples using the known

addition method. – During calibration, measure the least concentrated standard first,

and work up to the most concentrated. – The best method for preparation of standards is by serial

dilution. This procedure involves preparing an initial standard

that is diluted, using volumetric glassware, to prepare a second

standard solution. The second is similarly diluted to prepare a

third standard, and so on, until the desired range of standards

has been prepared. – Store all silver samples and standards away from light. – Verify this procedure by measuring a standard of known

concentration as an unknown or by spiking a sample with

silver standard. – Review section entitled GLP Measuring Hints.

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Direct Measurement Procedure using ISE Meter

See individual meter instruction manuals for more specific calibration information.

1. Prepare electrode(s) as described in Electrode Preparation.

2. Connect electrode(s) to the meter, and adjust the meter to

measure concentration.

3. Prepare two standards that bracket the expected sample range

and differ in concentration by a factor of ten. Standards can be

prepared in any concentration unit to suit the particular analysis

requirement. All standards should be at the same temperature

as the samples. For details on temperature effects on electrode

performance, refer to Temperature Effects.

4. Measure 100 mL of each standard and sample into separate

150 mL beakers. Add 2 mL ISA to each beaker.

NOTE: Other solution volumes may be used, as long as the ratio of solution to ISA remains 50:1. Stir thoroughly.

5. Rinse electrode(s) with distilled water, blot dry and place into the

beaker containing the most dilute standard. Wait for a stable

reading, then calibrate the meter to display the value of the

standard as described in the meter instruction manual.

6. Rinse electrode(s) with distilled water, blot dry, and place into

the beaker with the next standard. Wait for a stable reading, then

adjust the meter to display the value of this standard, as

described in the meter instruction manual.

7. Repeat step 6 for all standards, working from the least

concentrated to most concentrated standard.

8. Rinse electrode(s) with distilled water, blot dry, and place into

sample. The concentration will be displayed on the meter.

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Figure 2 Typical Silver Calibration Curve

In the direct measurement procedure, a calibration curve is constructed on semi-logarithmic paper. Electrode potentials of standard solutions are measured and plotted on the linear axis against their concentrations on the log axis. In the linear regions of the curves, only two standards are needed to determine a calibration curve. In nonlinear regions, more points must be taken. The direct measurement procedures in this manual are given for concentrations in the region of linear response. Low-level measurement procedures are given for measurements in the non-linear region. This curve is only used as an example. Actual mV values may differ.

550.0

450.0

400.0

350.0

300.0

250.0

200.0

-5

11010210

Molarity

ppm silver

-4

-3

-2

-1

500.0

Electrode potential (mV)

57 mV

10-fold change

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Direct Measurement Procedure using a meter with mV readout

1. Prepare electrode(s) as described in Electrode Preparation.

2. Connect electrode(s) to the meter, and adjust the meter to

measure mV.

3. Prepare two standards that bracket the expected sample range

and differ in concentration by a factor of ten. Standards can be

prepared in any concentration unit to suit the particular analysis

requirement. All standards should be at the same temperature

as the samples. For details on temperature effects on electrode

performance, refer to Temperature Effects.

4. Measure 100 mL of each standard and sample into separate

150 mL beakers. Add 2 mL ISA to each beaker.

NOTE: Other solution volumes may be used, as long as the ratio of solution to ISA remains 50:1. Stir thoroughly.

5. Rinse electrode(s) with distilled water, blot dry and place into the

beaker containing the most dilute standard. When a stable

reading is displayed,record the mV value and corresponding

standard concentration.

6. Rinse electrode(s) with distilled water, blot dry, and place

into the beaker with the next standard. When a stable reading

is displayed, record the mV value and corresponding

standard concentration.

7. Repeat step 6 for all standards, working from the

least concentrated to most concentrated standard.

8. Using semi-logarithmic graph paper, prepare a calibration curve

by plotting the millivolt values on the linear axis and the

standard concentration values on the logarithmic axis.

See Figure 2.

9. Rinse electrode(s) with distilled water, blot dry, and place into

sample. When a stable reading is displayed, record the

mV value.

10.Using the calibration curve prepared in step 8, determine the

unknown sample concentration.

Page 23

Low-Level Measurements

These procedures are for solutions with a silver concentration of less than 0.5 ppm or 4.6 x 10-6M Ag+, those within the non-linear range of the silver electrode. See Figure 2. In low-level measurements, at least three standards are required for calibration to compensate for the electrode’s non-linearity.

Measuring Hints

– Use plastic labware for low-level silver measurements. – For solutions low in silver but high in total ionic strength

(greater than 10

-1

M), perform the same procedure with one change: prepare a calibration solution with a composition similar to the sample.

– The choice of standard concentrations is important for obtaining

the best electrode performance and most rapid analysis time. Here are some guidelines:

• Ideally, standard concentrations should bracket the

expected sample concentrations.

• When measuring sub-ppm levels with Orion 920A, 720A,

710A, or 290A, take advantage of the autoblank feature. It does not require a zero standard, but can perform blank correction as long as the lowest standard concentration is in the non-linear range of the electrode. Electrodes are very slow in the absence of a measurable concentration and a multipoint calibration generally will be less accurate when “zero” is included as a standard. Standard concentrations should be chosen such that the lowest standard value is larger than the blank value obtained, and the second lowest standard should be at least twice that of the lowest. See your A-Series meter instruction manual for additional information on blank correction.

Page 24

• If using an ISE meter, such as the Orion EA 940, that

allows a blank solution value to be entered, it is recommended to do so. A blank solution is prepared with the same dilution water and ISA used when preparing calibration standards. This solution corrects for the curves non-linearity as well as for any background ion contamination that might be present in the standard solutions. When a blank value is entered, it represents the zero point of the curve, and each standard is measured against that blank.

• When not using an ISE meter, a calibration curve can be

drawn on semi-logarithmic graph paper, or the data can be processed at the discretion of the user by means of a spreadsheet or graphing program with a non-linear curve fitting feature.

• When using an ISE meter, such as the Orion 920A, 720A,

710A, or 290A, three calibration points are sufficient. If a calibration curve is prepared manually, additional points

may be helpful to facilitate drawing the curve. – Remember to stir all standards and samples at a uniform rate. – Typical response time for this electrode is approximately 1

minute. Low-level measurements may take longer to stabilize. Wait for 3 minutes or the meter’s “ready” signal, whichever takes longer, before calibrating the meter or recording the sample value.

– Review section entitled GLP Measuring Hints.

Page 25

Low-Level Measurement Procedure using ISE Meter

Follow the above procedure entitled Direct Measurement Procedure using ISE Meter except substitute low-level ISA (see

page 18). Use at least three calibration standards. Read the Measuring Hints section on pg. 21 in order to select appropriate standard concentrations. Refer to the meter instruction manual for detailed calibration procedures. If not using an Orion 920A, 720A, 710A, or 290A with the autoblank feature, preparation of a blank solution is recommended to ensure accurate results.

Low-Level Measurement Procedure using a meter with mV readout (see Table 3)

Set Up

1. Prepare electrode(s) as described in Electrode Preparation.

2. Connect electrode(s) to the meter. Set the meter to read mV.

3. Select a standard solution. Use either a 10 ppm silver standard

or a 10

-4

M silver solution.

4. Prepare a low-level ISA solution by diluting 20 mL of the

silver ionic strength adjustor, Orion 940011, to 100 mL with distilled water.

NOTE: use this low-level ISA for low-level measurements only.

Measurement

1. Measure 100 mL distilled water into 150 mL beaker. Add 1 mL

low-level ISA.

2. Rinse electrode(s) with distilled water, blot dry, and place into

beaker. Stir thoroughly.

3. Add increments of the 10 ppm or 10

-4

M standard to the beaker using steps outlined in Table 3. Record stable millivolt reading after each increment. On semi-logarithmic paper, plot the concentration (log axis) against the millivolt potential (linear axis). See Figure 2. Prepare a new calibration curve with fresh standards each day.

Page 26

4. Measure 100 mL of sample into a beaker. Add 1 mL low-level ISA. Rinse the electrode(s) with distilled water, blot dry, and place into the sample.

5. Stir thoroughly. When a stable reading is displayed, record the mV value.

6. Determine the sample concentration corresponding to the measured potential from the low-level calibration curve.

Table 3 Preparing a Calibration Curve For Low-Level Measurements making 10 ppm silver additions

Graduated Pipet Added Concentration

Step Size Volume ppm

11 mL 0.1 mL 0.01 21 mL 0.3 mL 0.04 31 mL 0.6 mL 0.10 42 mL 2.0 mL 0.30

Preparing a Calibration Curve For Low-Level Measurements making 10

-4

M silver additions

Graduated Pipet Added Concentration

Step Size Volume Molarity

11 mL 0.1 mL 1.0 x 10

-7

21 mL 0.3 mL 4.0 x 10

-7

31 mL 0.6 mL 1.0 x 10

-6

42 mL 2.0 mL 3.0 x 10

-6

Additions of 10 ppm or 10-4M standard to 100 mL distilled water, plus 1 mL low-level ISA.

Page 27

Known Addition

Known addition is a convenient technique for measuring samples in the linear range, greater than 0.5 ppm Ag+, because no calibration curve is needed. The sample potential is measured before and after addition of a standard solution. Many meters, such as the Orion 920A, have the known addition algorithms preprogrammed. This programming allows multiple standard additions to be made to the sample, thereby allowing the meter to calculate the electrode slope as well. Having the ability to read the sample concentration directly from the meter is a great convenience and ensures accuracy.

Measuring Hints

– Sample concentration should be known within a factor of three. – Concentration should approximately double as a result of the

first standard addition.

– With double or multiple known addition, the final addition should

be 10 to 100 times the sample concentration.

– All samples and standards should be at the same temperature. – Add 2 mL ISA to every 100 mL of sample before analysis. – Standard addition volume should be no more than 10% of the

sample volume, or standard should be pre-treated with ISA in a 50:1 ratio. See Table 4.

– Review section entitled GLP Measuring Hints.

Set-up

1. Prepare electrode(s) as described in Electrode Preparation.

2. Connect electrode(s) to the meter.

3. Prepare a standard solution that, upon addition to the sample, will cause the concentration of silver to double. Refer to Table 4 as a guideline.

4. Determine the slope of the electrode by performing the procedure under Checking Electrode Operation (Slope).

Page 28

Known Addition Measurement Procedure using an ISE meter with KA program

See individual meter instruction manual for more specific information.

1. Set the meter to measure in the known addition mode.

2. Measure 100 mL of sample into a beaker. Add 2 mL ISA. Stir thoroughly. Rinse electrode(s) with distilled water, blot dry, and place in sample solution.

3. When a stable reading is displayed, program the meter as described in the meter instruction manual.

4. Pipet the appropriate amount of standard solution into the beaker. Stir thoroughly.

5. When a stable reading is displayed, record the sample concentration.

Table 4 Standard Addition volumes

Volume of Addition Concentration of Standard

1 mL 100 x sample concentration 5 mL 20 x sample concentration 10 mL* 10 x sample concentration

* Most convenient volume to use.

Page 29

Known Addition Measurement Procedure using a meter with mV readout

1. Set the meter to millivolt mode.

2. Measure 100 mL of the sample into a 150 mL beaker. Add 2 mL ISA. Stir thoroughly.

3. Rinse electrode(s) with distilled water, blot dry, and place into beaker. When a stable reading is displayed, record the mV value as E

4. Pipet the appropriate amount of standard solution into the beaker. See Table 4. Stir thoroughly.

5. When a stable reading is displayed, record the mV value as E

Subtract the first reading from the second to find DE.

6. From Table 6, find the value Q, that corresponds to the change in potential, DE. To determine the original sample concentration, multiply Q by the concentration of the added standard:

Csam = Q*Cstd

where: Cstd = standard concentration

Csam = sample concentration Q = reading from known addition table

The table of Q values is calculated for a 10% volume change for electrodes with slopes of 57, 58, 59, 60 mV/ decade for silver. The equation for the calculation of Q for different slopes and volume changes is given below:

Q= p * r

(1+p)(10

∆E/S

)-1

where: Q = reading from known addition table

∆E = E

- E

S = slope of the electrode p = (volume of standard) / (volume of sample & ISA) r = (volume of sample & ISA) / (volume of sample)

Page 30

If it is more convenient, a simple spreadsheet can be set up to calculate known addition results, using any ratio of sample to addition. A typical worksheet is shown in Table 5. The numbers shown are examples, but the formulas and their locations should be copied exactly.

Table 5 Calculating known addition for silver samples using Lotus, Excel, or Quattro Spreadsheet

A B C

1 Enter Value 2 Vol. of Sample & ISA, mL: 102 3 Vol. of Addition, mL: 10 4 Concentrn. of Addition: 10 5 Vol. of Sample 100 6 Initial mV Reading 45.3 7 Final mV Reading 63.7 8 Electrode Slope 59.2 9 10 Derived Values 11 Delta E +C7 - C6 12 Solution Vol. Ratio +C3/C2 13 Antilog Term +10^ (C11/C8) 14 Sample Vol. Ratio +C2/C5 15 Q Term +C12*C14/

{

[(1 +C12)*C13]-1

}

16 Calculated Initial Conc. in

same units as addition: +C15*C4

NOTE: for Excel, use = instead of + at start of formula

Page 31

Table 6 Known Addition Table for an added volume one-tenth the total volume. Slopes, in the column headings, are in units of mV/decade.

Q, Concentration Ratio

(slope)

-∆E 57.2 58.2 59.2 60.1

5.0 0.2917 0.2957 0.2996 0.3031

5.2 0.2827 0.2867 0.2906 0.2940

5.4 0.2742 0.2781 0.2820 0.2854

5.6 0.2662 0.2700 0.2738 0.2772

5.8 0.2585 0.2623 0.2660 0.2693

6.0 0.2512 0.2550 0.2586 0.2619

6.2 0.2443 0.2480 0.2516 0.2548

6.4 0.2377 0.2413 0.2449 0.2480

6.6 0.2314 0.2349 0.2384 0.2416

6.8 0.2253 0.2288 0.2323 0.2354

7.0 0.2196 0.2230 0.2264 0.2295

7.2 0.2140 0.2174 0.2208 0.2238

7.4 0.2087 0.2121 0.2154 0.2184

7.6 0.2037 0.2070 0.2102 0.2131

7.8 0.1988 0.2020 0.2052 0.2081

8.0 0.1941 0.1973 0.2005 0.2033

8.2 0.1896 0.1927 0.1959 0.1987

8.4 0.1852 0.1884 0.1914 0.1942

8.6 0.1811 0.1841 0.1872 0.1899

8.8 0.1770 0.1801 0.1831 0.1858

9.0 0.1732 0.1762 0.1791 0.1818

9.2 0.1694 0.1724 0.1753 0.1779

9.4 0.1658 0.1687 0.1716 0.1742

9.6 0.1623 0.1652 0.1680 0.1706

9.8 0.1590 0.1618 0.1646 0.1671

10.0 0.1557 0.1585 0.1613 0.1638

10.2 0.1525 0.1553 0.1580 0.1605

10.4 0.1495 0.1522 0.1549 0.1573

10.6 0.1465 0.1492 0.1519 0.1543

10.8 0.1437 0.1463 0.1490 0.1513

11.0 0.1409 0.1435 0.1461 0.1485

11.2 0.1382 0.1408 0.1434 0.1457

11.4 0.1356 0.1382 0.1407 0.1430

11.6 0.1331 0.1356 0.1381 0.1404

11.8 0.1306 0.1331 0.1356 0.1378

12.0 0.1282 0.1307 0.1331 0.1353

12.2 0.1259 0.1283 0.1308 0.1329

12.4 0.1236 0.1260 0.1284 0.1306

12.6 0.1214 0.1238 0.1262 0.1283

12.8 0.1193 0.1217 0.1240 0.1261

13.0 0.1172 0.1195 0.1219 0.1239

13.2 0.1152 0.1175 0.1198 0.1218

13.4 0.1132 0.1155 0.1178 0.1198

13.6 0.1113 0.1136 0.1158 0.1178

13.8 0.1094 0.1117 0.1139 0.1159

Page 32

Table 6 (continued)

Q, Concentration Ratio

(slope)

-∆E 57.2 58.2 59.2 60.1

14.0 0.1076 0.1098 0.1120 0.1140

14.2 0.1058 0.1080 0.1102 0.1121

14.4 0.1041 0.1063 0.1084 0.1103

14.6 0.1024 0.1045 0.1067 0.1086

14.8 0.1008 0.1029 0.1050 0.1069

15.0 0.0992 0.1012 0.1033 0.1052

15.5 0.0953 0.0973 0.0994 0.1012

16.0 0.0917 0.0936 0.0956 0.0974

16.5 0.0882 0.0902 0.0921 0.0938

17.0 0.0850 0.0869 0.0887 0.0904

17.5 0.0819 0.0837 0.0856 0.0872

18.0 0.0790 0.0808 0.0825 0.0841

18.5 0.0762 0.0779 0.0797 0.0813

19.0 0.0736 0.0753 0.0770 0.0785

19.5 0.0711 0.0727 0.0744 0.0759

20.0 0.0687 0.0703 0.0719 0.0734

20.5 0.0664 0.0680 0.0696 0.0710

21.0 0.0642 0.0658 0.0673 0.0687

21.5 0.0621 0.0637 0.0652 0.0666

22.0 0.0602 0.0617 0.0631 0.0645

22.5 0.0583 0.0597 0.0612 0.0625

23.0 0.0564 0.0579 0.0593 0.0606

23.5 0.0547 0.0561 0.0575 0.0588

24.0 0.0530 0.0544 0.0558 0.0570

24.5 0.0514 0.0528 0.0541 0.0553

25.0 0.0499 0.0512 0.0525 0.0537

25.5 0.0484 0.0497 0.0510 0.0522

26.0 0.0470 0.0483 0.0495 0.0507

26.5 0.0456 0.0469 0.0481 0.0492

27.0 0.0443 0.0455 0.0468 0.0479

27.5 0.0431 0.0443 0.0455 0.0465

28.0 0.0419 0.0430 0.0442 0.0452

28.5 0.0407 0.0418 0.0430 0.0440

29.0 0.0395 0.0407 0.0418 0.0428

29.5 0.0385 0.0396 0.0407 0.0417

30.0 0.0374 0.0385 0.0396 0.0406

30.5 0.0364 0.0375 0.0385 0.0395

31.0 0.0354 0.0365 0.0375 0.0384

31.5 0.0345 0.0355 0.0365 0.0374

32.0 0.0335 0.0345 0.0356 0.0365

32.5 0.0327 0.0336 0.0346 0.0355

33.0 0.0318 0.0328 0.0337 0.0346

33.5 0.0310 0.0319 0.0329 0.0337

34.0 0.0302 0.0311 0.0320 0.0329

34.5 0.0294 0.0303 0.0312 0.0321

35.0 0.0286 0.0295 0.0305 0.0313

35.5 0.0279 0.0288 0.0297 0.0305

Page 33

Table 6 (continued)

Q, Concentration Ratio

(slope)

-∆E 57.2 58.2 59.2 60.1

36.0 0.0272 0.0281 0.0290 0.0298

36.5 0.0265 0.0274 0.0282 0.0290

37.0 0.0258 0.0267 0.0275 0.0283

37.5 0.0252 0.0260 0.0269 0.0276

38.0 0.0246 0.0254 0.0262 0.0270

38.5 0.0240 0.0248 0.0256 0.0263

39.0 0.0234 0.0242 0.0250 0.0257

39.5 0.0228 0.0236 0.0244 0.0251

40.0 0.0223 0.0230 0.0238 0.0245

40.5 0.0217 0.0225 0.0232 0.0239

41.0 0.0212 0.0219 0.0227 0.0234

41.5 0.0207 0.0214 0.0221 0.0228

42.0 0.0202 0.0209 0.0216 0.0223

42.5 0.0197 0.0204 0.0211 0.0218

43.0 0.0192 0.0199 0.0206 0.0213

43.5 0.0188 0.0195 0.0202 0.0208

44.0 0.0183 0.0190 0.0197 0.0203

44.5 0.0179 0.0186 0.0192 0.0198

45.0 0.0175 0.0181 0.0188 0.0194

45.5 0.0171 0.0177 0.0184 0.0190

46.0 0.0167 0.0173 0.0179 0.0185

46.5 0.0163 0.0169 0.0175 0.0181

47.0 0.0159 0.0165 0.0171 0.0177

47.5 0.0156 0.0162 0.0168 0.0173

48.0 0.0152 0.0158 0.0164 0.0169

48.5 0.0148 0.0154 0.0160 0.0166

49.0 0.0145 0.0151 0.0157 0.0162

49.5 0.0142 0.0147 0.0153 0.0158

50.0 0.0139 0.0144 0.0150 0.0155

50.5 0.0135 0.0141 0.0146 0.0151

51.0 0.0132 0.0138 0.0143 0.0148

51.5 0.0129 0.0135 0.0140 0.0145

52.0 0.0126 0.0132 0.0137 0.0142

52.5 0.0124 0.0129 0.0134 0.0139

53.0 0.0121 0.0126 0.0131 0.0136

53.5 0.0118 0.0123 0.0128 0.0133

54.0 0.0116 0.0120 0.0125 0.0130

54.5 0.0113 0.0118 0.0123 0.0127

55.0 0.0110 0.0115 0.0120 0.0125

55.5 0.0108 0.0113 0.0118 0.0122

56.0 0.0106 0.0110 0.0115 0.0119

56.5 0.0103 0.0108 0.0113 0.0117

57.0 0.0101 0.0106 0.0110 0.0114

57.5 0.0099 0.0103 0.0108 0.0112

58.0 0.0097 0.0101 0.0105 0.0110

58.5 0.0095 0.0099 0.0103 0.0107

59.0 0.0093 0.0097 0.0101 0.0105

59.5 0.0091 0.0095 0.0099 0.0103

60.0 0.0089 0.0093 0.0097 0.0101

Page 34

Low-Level Chloride Titration

The electrode is a highly sensitive endpoint detector for titration of silver samples with a halide standard (or vice versa). The low-level chloride titration is an example of this type of measurement. Titrations are more time-consuming than direct electrode measurement, but results are more accurate and reproducible. With careful technique, titrations accurate to ± 0.1% of the total chloride ion concentration of the sample can be performed. The Orion 960 Autochemistry System may be used to automate these titrations.

Figure 3 Typical Titration of 25 mL (before dilution) 0.001 M Chloride Sample with 0.01 M AgNO

10-fold change

500

400

300

200

ml 0.01 M AgNO

0 1 2 3 4 5 6 7 8 9 10

Page 35

Set-up

1. Prepare electrode(s) as described in Electrode Preparation.

2. Connect electrode(s) to the meter.

3. Prepare a titrant solution 10 - 20 times as concentrated as the sample by dilution of the 0.1 M silver solution.

Measurement

1. Place 50 mL of sample into a 150 mL beaker. Place electrode(s) in the sample. Stir thoroughly.

2. Using a 10 mL burette, add increments of titrant and plot electrode potential against mL of titrant added. The endpoint is the point of greatest slope (inflection point). See Figure 3.

3. Calculate the sample concentration before dilution:

sam

= Ct(Vt/V

sam

)

where: C

sam

= sample concentration

= titrant concentration

sam

= sample volume

= titrant volume added at endpoint.

Page 36

Low-Level Cyanide Indicator Method

The Ag/S electrode can be used for cyanide measurements down to

0.03 ppm CN-. A small amount of KAg(CN)2is added to the

solution as an indicator. The ion Ag(CN)

dissociates to form some silver and cyanide ions, and the electrode measures the silver concentration. Since the degree of dissociation of the ion depends on the free cyanide concentration, measurement of the silver concentration is an indirect measure of the cyanide concentration.

Cyanide complexed by copper, nickel, cobalt, or iron cannot be measured directly with this method. These complexes may be broken by distillation according to ASTM Method D 2036, Section 12.2.

Sulfide ion is an interference for the method, but it can be removed by precipitation with cadmium.

Set-up

1. Prepare electrode(s) as described in Electrode Preparation.

2. Connect electrode(s) to the meter.

3. Prepare the following solutions:

Ethylemediamine – anhydrous (98% purity or better) for the removal of formaldehyde.

Silver Nitrate Titrant – (1 mL = 1 mg CN

) Crush approximately 5 g of reagent grade silver nitrate (AgNO3) crystals and dry at 150 °C for 1 hour. Dissolve 3.265 g in distilled water and dilute to 1 liter.

NaOH Diluent – Dissolve 25 g reagent grade sodium hydroxide (NaOH) in distilled water and dilute to 1 liter. For diluting cyanide standard solutions.

Silver Potassium Cyanide [KAg(CN)

] – Reagent grade or

equivalent. Available from suppliers of electroplating chemicals. Indicator/Buffer – Add 33 g of reagent grade disodium hydrogen

phosphate (Na

HPO4 • 7H2O) in about 80 mL water. Stir for about one half hour to saturate the solution with phosphate. Add 2.2 g of reagent grade sodium hydroxide (NaOH),

0.1 g of silver potassium cyanide [KAg(CN)2], and 3.4 mL of ethylemediamine, and dissolve by thorough mixing with distilled water. Dilute to 100 mL with distilled water. Check the solution before use for precipitation of any solids; discard if a precipitate appears.

Page 37

Potassium Cyanide – Stock solution (1000 ppm, 1 mL = approximately 1 mg CN

) Dissolve approximately 2 g of reagent grade sodium hydroxide (NaOH) and 2.51 g of reagent grade potassium cyanide (KCN) in 1 liter of distilled water.

CAUTION: KCN is highly toxic. Avoid contact or inhalation.

Standardization of KCN Stock Solution

1. Standardize the KCN stock solution by titration with silver nitrate titrant. Pipet 20 mL of the KCN stock solution into a 150 mL beaker. Immerse the electrode(s) and stir gently.

2. Fill a 25 mL burette with the silver nitrate titrant.

3. Add increments of 0.5 to 1 mL in the beginning of the titration and about 0.1 to 0.25 mL in the region of the endpoint. Continue the titration 3 - 4 mL past the endpoint.

4. Record the solution potential after each addition of titrant and plot mL of titrant added versus mV readings on standard graph paper. The point of inflection is taken as the endpoint.

5. Prepare a blank solution by dissolving 2 g reagent grade NaOH per liter. Titrate 20 mL of blank solution according to instructions above.

6. Calculate the cyanide concentration of the stock solutions follows:

, (ppm) = (A - B) x 1000/ C

where: A = mL of titrant added at the endpoint

(cyanide solution) B = mL of titrant added at the endpoint (blank) C = mL of cyanide stock solution used for

the titration

7. Standardize the stock solution each week because the solution loses strength gradually.

8. Prepare a 100 ppm cyanide standard daily by dilution of the stock solution with NaOH diluent. The 100 ppm solution is prepared by pipetting a volume, V, into a 100 mL volumetric flask. The volume, V, is calculated from:

V = 10000/D

where D = concentration (ppm) of cyanide stock solution

9. Prepare 10 and 1 ppm standards daily by serial dilution with the NaOH diluent. For lower levels of cyanide, prepare 0.1 and

0.01 ppm standards as well.

Page 38

Measurement of Sample

Set-up

1. Prepare electrode(s) as described in Electrode Preparation.

2. Connect electrode(s) to the meter.

3. Use the two standards prepared in step 9. Standards should be at the same temperature as the samples. For details on temperature effects on electrode performance, refer to

Temperature Effects.

Indicator method procedure using ISE Meter

See individual meter instruction manual for more specific calibration information.

1. Measure 100 mL of each standard and sample into separate 150 mL beakers. Add 2 mL Indicator/ Buffer to each beaker. Stir thoroughly.

2. Rinse electrode(s) with distilled water, blot dry and place into the beaker containing the most dilute standard. Wait for a stable reading, then calibrate the meter to display the value of the standard as described in the meter instruction manual.

3. Rinse electrode(s) with distilled water, blot dry, and place into the beaker with the next standard. Wait for a stable reading, then adjust the meter to display the value of this standard, as described in the meter instruction manual.

4. Repeat step 3 for all standards, working from the least concentrated to most concentrated standard. Slope will be between -116 to -122 mV/decade.

5. Rinse electrode(s) with distilled water, blot dry, and place into sample. The concentration will be displayed on the meter.

Page 39

Indicator method procedure using a meter with mV readout

1. Measure 100 mL of each standard and sample into separate 150 mL beakers. Add 2 mL Indicator/ Buffer to each beaker. Stir thoroughly.

2. Rinse electrode(s) with distilled water, blot dry and place into the beaker containing the most dilute standard. When a stable reading is displayed, record the mV value and corresponding standard concentration.

3. Rinse electrode(s) with distilled water, blot dry, and place into the beaker with the next standard. When a stable reading is displayed, record the mV value and corresponding standard concentration.

4. Repeat step 3 for all standards, working from the least concentrated to most concentrated standard.

5. Using semi-logarithmic graph paper, prepare a calibration curve by plotting the millivolt values on the linear axis and the standard concentration values on the logarithmic axis. See Figure 3.

6. Rinse electrode(s) with distilled water, blot dry, and place into sample. When a stable reading is displayed, record the mV value.

7. Using the calibration curve prepared in step 5, determine the unknown sample concentration.

Page 40

SULFIDE MEASUREMENT PROCEDURES

Direct Measurement

The following direct measurement procedures are recommended for “high-level” measurements. All samples must be in the electrode’s linear range, greater than 0.32 ppm or 10

-5

M S2-. A two point calibration is sufficient, though more points can be used if desired. With ISE meters, such as the Orion 920A, 720A, 710A, or 290A, sample concentrations can be read directly from the meter. Refer to the meter instruction manual for calibration details. When using a mV meter, a calibration curve can be prepared on semilogarithmic graph paper, or a linear regression (against logarithmic concentration values) can be performed at the user’s discretion using a spreadsheet or graphing program.

Measuring Hints

– Standard concentrations should bracket the expected

sample concentrations.

– Always dilute samples and standards in a 1:1 ratio with SAOB II.

For example, 25 mL of sample and 25 mL of SAOB II.

– For high ionic strength samples, having an ionic strength of

0.1 M or greater, prepare standards with a composition similar to that of the samples, or measure the samples using the known addition method.

– During calibration, measure the least concentrated standard first,

and work up to the most concentrated.

– The best method for preparation of standards is by serial

dilution. This procedure involves preparing an initial standard that is diluted, using volumetric glassware, to prepare a second standard solution. The second is similarly diluted to prepare a third standard, and so on, until the desired range of standards has been prepared.

– Dilute sulfide samples 1:1 with SAOB II as they are collected,

except when analate subtraction is the measurement technique.

NOTE: If samples have been preserved with SAOB II DO NOT add more SAOB II before measuring.

– Always use deaerated water when preparing sulfide standards to

prevent the oxidation of sulfide.

– Verify this procedure by measuring a standard of known

concentration as an unknown or by spiking a sample with sulfide standard.

– Review section entitled GLP Measuring Hints.

Page 41

Direct Measurement Procedure using ISE Meter

See individual meter instruction manuals for more specific calibration information.

1. Prepare electrode(s) as described in Electrode Preparation.

2. Connect electrode(s) to the meter, and adjust the meter to

measure concentration.

3. Prepare two standards that bracket the expected sample range

and differ in concentration by a factor of ten. Standards can be prepared in any concentration unit to suit the particular analysis requirement. All standards should be at the same temperature as the samples. For details on temperature effects on electrode performance, refer to Temperature Effects.

4. Measure 25 mL of each standard and sample into separate

150 mL beakers. Add 25 mL SAOB II to each beaker.

NOTE: Other solution volumes may be used, as long as the ratio of solution to SAOB II remains 1:1.

Stir thoroughly.

5. Rinse electrode(s) with distilled water, blot dry and place into

the beaker containing the most dilute standard. Wait for a stable reading, then calibrate the meter to display the value of the standard as described in the meter instruction manual.

6. Rinse electrode(s) with distilled water, blot dry, and place into

the beaker with the next standard. Wait for a stable reading, then adjust the meter to display the value of this standard, as described in the meter instruction manual.

7. Repeat step 6 for all standards, working from the least

concentrated to most concentrated standard.

8. Rinse electrode(s) with distilled water, blot dry, and place into

sample. The concentration will be displayed on the meter.

Page 42

Figure 4 Typical Sulfide Calibration Curve

-790.0

-780.0

-770.0

-760.0

-750.0

-740.0

-730.0

-5

0.1 1 10 10

Molarity

ppm sulfide

-4

-3

-2

-1

-800.0

-840.0

-830.0

-820.0

-810.0

-850.0

Electrode potential (mV)

-28 mV

10-fold change

Page 43

Direct Measurement Procedure using a meter with mV readout

1. Prepare electrode(s) as described in Electrode Preparation.

2. Connect electrode(s) to the meter, and adjust the meter to

measure mV.

3. Prepare two standards that bracket the expected sample range

4. Measure 25 mL of each standard and sample into separate

150 mL beakers. Add 25 mL SAOB II to each beaker.

NOTE: Other solution volumes may be used, as long as the ratio of solution to SAOB II remains 1:1.

Stir thoroughly.

5. Rinse electrode(s) with distilled water, blot dry and place into the

beaker containing the most dilute standard. When a stable reading is displayed, record the mV value and corresponding standard concentration.

6. Rinse electrode(s) with distilled water, blot dry, and place

into the beaker with the next standard. When a stable reading is displayed, record the mV value and corresponding standard concentration.

7. Repeat step 6 for all standards, working from the least

concentrated to most concentrated standard.

8. Using semi-logarithmic graph paper, prepare a calibration

curve by plotting the millivolt values on the linear axis and the standard concentration values on the logarithmic axis. See Figure 4.

9. Rinse electrode(s) with distilled water, blot dry, and place

into sample. When a stable reading is displayed, record the mV value.

10.Using the calibration curve prepared in step 8, determine the

unknown sample concentration.

Page 44

Analate Subtraction Measurements

Analate subtraction is recommended for occasional sulfide measurements because it uses a silver standard solution rather than the easily oxidized sulfide standard solution. The sample must not contain species that react with silver (e.g., halide ions or SAOB II). All concentration units are moles per liter. Use Table 2 to convert to ppm after measurement.

NOTE: DO NOT dilute sample with SAOB II for this procedure.

Set-up

1. Prepare electrode(s) as described in Electrode Preparation.

2. Connect electrode(s) to the meter.

3. Prepare a silver standard solution about one to one half the

expected sample sulfide concentration by diluting 0.1 M silver nitrate standard. Add 2 mL ISA (Orion 940011) to every 100 mL of standard.

Analate subtraction procedure using an ISE meter

See individual meter instruction manuals for more specific information.

1. Measure 100 mL of the silver standard into a beaker. Rinse

electrode(s) with distilled water, blot dry, and place in standard solution. Stir thoroughly.

2. When a stable reading is displayed, calibrate the meter as

described in the meter instruction manual.

3. Pipet 10 mL of sulfide sample into the silver standard.

Stir thoroughly.

4. When a stable reading is displayed, record the

sample concentration.

Page 45

Analate subtraction procedure using a meter with mV readout

1. Adjust the meter to measure mV.

2. Measure 100 mL of the silver standard into a beaker. Rinse

electrode(s) with distilled water, blot dry, and place in standard solution. Stir thoroughly.

3. When a stable reading is displayed, record the mV value.

4. Pipet 10 mL of sulfide sample into the silver standard.

Stir thoroughly.

5. When a stable reading is displayed, record the mV value.

6. Determine the potential change, ∆E, by subtracting the first

reading from the second.

7. Find the concentration ratio, Q, corresponding to the potential

change, E, in Table 7. Calculate the sample sulfide concentration in moles per liter:

Csam = 0.5QC

std

where: C

sam

= sample concentration Q= concentration ratio from Table 7 C

std

= concentration of silver standard in moles/liter

Page 46

Table 7 Analate Subtraction Table Slopes, in the column headings, are in units of mV/decade

Q, Concentration Ratio

(slope)

-∆E 57.2 58.2 59.2 60.1

5.0 0.503 0.487 0.472 0.458

5.2 0.539 0.523 0.507 0.493

5.4 0.575 0.558 0.542 0.527

5.6 0.610 0.593 0.576 0.561

5.8 0.645 0.628 0.611 0.595

6.0 0.680 0.662 0.645 0.629

6.2 0.715 0.696 0.679 0.662

6.4 0.749 0.730 0.712 0.695

6.6 0.783 0.764 0.745 0.728

6.8 0.817 0.797 0.778 0.761

7.0 0.851 0.830 0.811 0.793

7.2 0.884 0.863 0.843 0.825

7.4 0.917 0.896 0.876 0.857

7.6 0.950 0.928 0.908 0.888

7.8 0.982 0.960 0.939 0.920

8.0 1.014 0.992 0.971 0.951

8.2 1.046 1.024 1.002 0.982

8.4 1.078 1.055 1.033 1.012

8.6 1.109 1.086 1.064 1.043

8.8 1.141 1.117 1.094 1.073

9.0 1.172 1.148 1.124 1.103

9.2 1.202 1.178 1.154 1.133

9.4 1.233 1.208 1.184 1.162

9.6 1.263 1.238 1.214 1.191

9.8 1.293 1.268 1.243 1.221

10.0 1.323 1.297 1.272 1.249

10.2 1.352 1.326 1.301 1.278

10.4 1.381 1.355 1.330 1.306

10.6 1.410 1.384 1.358 1.334

10.8 1.439 1.412 1.386 1.362

11.0 1.468 1.441 1.414 1.390

11.2 1.496 1.469 1.442 1.418

11.4 1.524 1.497 1.470 1.445

11.6 1.552 1.524 1.497 1.472

11.8 1.580 1.552 1.524 1.499

12.0 1.607 1.579 1.551 1.526

12.2 1.634 1.606 1.578 1.552

12.4 1.661 1.633 1.605 1.579

12.6 1.688 1.659 1.631 1.605

12.8 1.715 1.685 1.657 1.631

13.0 1.741 1.712 1.683 1.656

13.2 1.767 1.737 1.709 1.682

13.4 1.793 1.763 1.734 1.707

13.6 1.819 1.789 1.759 1.732

13.8 1.844 1.814 1.784 1.757

14.0 1.870 1.839 1.809 1.782

14.2 1.895 1.864 1.834 1.806

14.4 1.920 1.889 1.859 1.831

14.6 1.944 1.913 1.883 1.855

14.8 1.969 1.938 1.907 1.879

15.0 1.993 1.962 1.931 1.903

15.5 2.053 2.021 1.990 1.961

16.0 2.112 2.080 2.048 2.019

16.5 2.169 2.137 2.105 2.076

17.0 2.226 2.193 2.161 2.131

17.5 2.281 2.248 2.215 2.185

Page 47

Q, Concentration Ratio

(slope)

-∆E 57.2 58.2 59.2 60.1

18.0 2.335 2.302 2.269 2.239

18.5 2.388 2.355 2.322 2.291

19.0 2.440 2.406 2.373 2.342

19.5 2.491 2.457 2.424 2.393

20.0 2.541 2.507 2.473 2.442

20.5 2.590 2.556 2.522 2.491

21.0 2.638 2.604 2.570 2.538

21.5 2.685 2.651 2.617 2.585

22.0 2.731 2.697 2.663 2.631

22.5 2.777 2.742 2.708 2.676

23.0 2.821 2.786 2.752 2.720

23.5 2.864 2.829 2.795 2.763

24.0 2.907 2.872 2.837 2.805

24.5 2.949 2.914 2.879 2.847

25.0 2.990 2.954 2.920 2.888

25.5 3.030 2.995 2.960 2.928

26.0 3.069 3.034 2.999 2.967

26.5 3.107 3.072 3.038 3.006

27.0 3.145 3.110 3.076 3.044

27.5 3.182 3.147 3.113 3.081

28.0 3.218 3.183 3.149 3.117

28.5 3.254 3.219 3.185 3.153

29.0 3.289 3.254 3.220 3.188

29.5 3.323 3.288 3.254 3.222

30.0 3.356 3.322 3.288 3.256

31.0 3.421 3.387 3.353 3.321

32.0 3.483 3.449 3.416 3.384

33.0 3.543 3.509 3.476 3.445

34.0 3.601 3.567 3.534 3.503

35.0 3.656 3.623 3.590 3.560

36.0 3.709 3.676 3.644 3.614

37.0 3.760 3.728 3.696 3.666

38.0 3.809 3.777 3.745 3.716

39.0 3.856 3.824 3.793 3.764

40.0 3.901 3.870 3.839 3.811

41.0 3.944 3.914 3.884 3.855

42.0 3.986 3.956 3.926 3.898

43.0 4.026 3.996 3.967 3.940

44.0 4.064 4.035 4.007 3.979

45.0 4.101 4.073 4.045 4.018

46.0 4.137 4.109 4.081 4.055

47.0 4.171 4.143 4.116 4.090

48.0 4.203 4.177 4.150 4.124

49.0 4.235 4.209 4.182 4.157

51.0 4.294 4.269 4.243 4.219

52.0 4.322 4.297 4.272 4.249

53.0 4.349 4.324 4.300 4.277

54.0 4.374 4.351 4.327 4.304

55.0 4.399 4.376 4.352 4.330

56.0 4.423 4.400 4.377 4.355

57.0 4.446 4.423 4.401 4.380

58.0 4.467 4.446 4.424 4.403

59.0 4.488 4.467 4.446 4.425

60.0 4.509 4.488 4.467 4.447

Page 48

Sulfide Titration

Sulfide may be titrated with a lead perchlorate standard solution. For sulfide measurements, titrations produce an extremely sharp endpoint, even at low levels of sulfide. Titration is the recommended measurement method for sulfide samples. Titrations are more time-consuming than direct electrode measurement, but results are more accurate and reproducible. With careful technique, titrations accurate to ± 0.1% of the total sulfide ion concentration of the sample can be performed. The Orion 960 Autochemistry System may be used to automate these titrations.

Figure 5 Typical Titration of 25 mL (before dilution) 0.03 M Sulfide Sample with 0.1 M Pb(ClO

4)2

Set-up

1. Prepare electrode(s) as described in Electrode Preparation.

2. Connect electrodes to the meter.

3. Prepare a lead titrant solution 10 - 20 times as concentrated as the sample by dilution of the Orion 0.1 M lead perchlorate solution, 948206.

10-fold change

-800

-700

-600

-500

ml 0.1 M Pb(ClO

4)2

0 1 2 3 4 5 6 7 8 9 10

Page 49

Measurement

1. Place 50 mL of sample (previously diluted 1:1 with SAOB II) into a 150 mL beaker. Place electrode(s) in the sample. Stir thoroughly.

2. Using a 10 mL burette, add increments of titrant and plot electrode potential against mL of titrant added. The endpoint is the point of greatest slope (inflection point). See Figure 5.

3. Calculate the sample concentration before dilution:

Csam = C

t(Vt/Vsam

)

where: C

sam

= sample concentration

= titrant concentration

sam

= sample volume

= titrant volume added at endpoint.

Page 50

ELECTRODE STORAGE

Orion 94-16 Silver/Sulfide Half-Cell Electrode

Orion 94-16 Silver/Sulfide Half-Cell Electrode should be rinsed thoroughly and stored in distilled water or in the air. When storing for long periods of time, replace the cap to protect the sensing element and store dry.

Orion 96-16 Sure-Flow Combination Silver/Sulfide Electrode

The solution in the Orion 96-16 Combination Silver/Sulfide Electrode should not be allowed to evaporate, causing crystallization.

For short periods of time (up to one week):

Store the electrode in distilled water.

For storage longer than one week:

Drain the electrode, flush the inside with distilled water and store dry with the cap on to protect the sensing element.

Orion 90-02 Double Junction Reference Electrode

Orion 90-02 Reference Electrode may be stored in air between sample measurements (up to two hours).

For short periods of time (up to one week):

90-02 should be stored in filling solution. Distilled water is also an acceptable storage solution. The solutions inside the electrode should not be allowed to evaporate causing crystallization.

For storage longer than one week:

Drain both chambers of the reference electrode, flush the inside with distilled water, and store dry.

Page 51

ELECTRODE MAINTENANCE

Silver/Sulfide Electrode Cleaning Procedure

Place a drop of liquid dish detergent on a moist cloth or tissue and gently rub over the sensing element. Rinse with distilled water.

Silver/Sulfide Electrode Polishing Procedure

To be used when electrode becomes sluggish or drifty and above cleaning procedure does not improve electrode response.

1. Cut off a 1-inch length of the polishing strip, Orion 948201.

2. Hold electrode with the sensing element facing upwards.

3. Place a few drops of distilled water on the sensing element surface.

4. With the frosted side down, place the polishing strip on the sensing element using light finger pressure.

5. Rotate the electrode for about 30 seconds.

6. Rinse and soak in a 1 ppm or 10

-5

M silver standard solution for

about two minutes before use.

Disassembly and Cleaning of 96-16 Sure-Flow Combination Silver/Sulfide Electrode

Disassembly is not normally required or recommended. When the area between the electrode sleeve and inner cone becomes clogged with sample or precipitate from filling solution, the chamber can be cleaned by flushing out with filling solution. (Hold the electrode by the cap with one hand and push the outer sleeve of the electrode up into the cap to drain the chamber.) If the chamber is not completely clean, repeat the procedure. Refill with the appropriate filling solution.

Page 52

If a more thorough cleaning is required, the electrode can be disassembled using the following instructions:

1. Rinse the outer body under warm running water.

2. Hold the electrode body by the cap with one hand and push the outer sleeve of the electrode up into the cap to drain the chamber.

3. Unscrew the cap, slide the cap and epoxy-coated spring up along the cable.

4. Hold the outer sleeve with one hand and firmly push down on the threaded portion with the thumb and forefinger to separate the inner body from the sleeve.

5. Grasp the cone with a clean tissue and withdraw the body from the sleeve with a gentle twisting motion.

NOTE: Do not touch the AgCl pellet above the cone as it may cause damage to the pellet.

Rinse the outside of the electrode body and the entire sleeve with distilled water. Allow to air dry.

Reassemble

1. Moisten the O-ring on the electrode body with a drop of filling solution. Insert screw-thread end of the electrode body into the tapered, ground end of sleeve.

2. Push body into sleeve with a gentle twisting motion until bottom surface of inner cone is flush with the tapered end of the sleeve.

3. Place the spring on the electrode body and screw on the cap. Refill with filling solution. The electrode is now ready for use.

Page 53

TROUBLESHOOTING

Troubleshooting Checklist

Symptom Possible Causes

Off-scale or Defective meter Over-range Defective electrode reading Electrodes not plugged in properly

Reference electrode junction is dry Reference electrode chamber not filled Air bubble on electrode Electrodes not in solution

Noisy or Defective meter unstable Meter or stirrer improperly grounded readings Air bubble on electrode (readings Wrong reference electrode continuously ISA/SAOB II not used or rapidly changing)

Drift (Reading Samples and standards at different slowly changing temperatures in one direction) Sensing element dirty or etched

Sulfide being oxidized

(drift in positive direction)

Incorrect reference filling solution

Page 54

Solution

Check meter with shorting strap

(See meter instruction manual) Refer to Troubleshooting Guide Unplug electrodes and reseat Hold reference electrode and push cap to expel a few

drops of filling solution Be sure reference electrode chamber is filled.

See Electrode Preparation. Remove air bubble on electrode by gently tapping it. Put electrodes in solution

Check meter with shorting strap

(See meter instruction manual) Check meter and stirrer for grounding Check Using the Electrode Remove air bubble on electrode by gently tapping it. Use appropriate reference electrode.

See Required Equipment. Do not use calomel or Ag/AgCl

(frit-or fiber-type) reference electrode Use recommended ISA, Orion 940011, for silver analyses

or SAOB II, Orion 941609, for sulfide analyses. Use

prepared indicator buffer for cyanide analyses.

Allow solutions to come to room temperature

before measurement Polish sensing element (see Electrode Maintenance) Use recommended filling solution.

See Electrode Preparation.

Page 55

Troubleshooting Checklist (Con‘t)

Symptom Possible Causes

Low slope Electrodes not properly conditioned or No slope Standards contaminated or incorrectly made

ISA or SAOB II not used Standard used as ISA Electrode exposed to interferences

“Wrong Answer” Incorrect scaling of semilog paper (But calibration Incorrect sign curve is OK) Incorrect standards

Wrong units used Complexing agents in sample

Page 56

Solution

Prepare fresh standards Use recommended ISA, Orion 940011, or SAOB II, Orion

941609 Use ISA! Refer to Troubleshooting Guide

Plot millivolts on the linear axis. On the log axis, be sure

concentration numbers within each decade are

increasing with increasing concentration Be sure to note sign of millivolt value correctly Prepare fresh standards Apply correct conversion factor:

-3

M = 32.1 ppm as S2-= 2 x 10-3N (S2-)

-3

M = 108 ppm Ag

Use known addition or titration techniques, or a

decomplexing procedure such as SAOB II for

sulfide analyses

For additional information on blank correction with your A-Series meter, see your meter operations manual.

Page 57

Troubleshooting Guide

The most important principle in troubleshooting is to isolate the components of the system and check each in turn. The components of the system are: 1) Meter 2) Electrodes 3) Standard 4) Sample and 5) Technique.

See also GLP Measuring Hints section.

Meter

The meter is the easiest component to eliminate as a possible cause of error. Orion meters are provided with an instrument checkout procedure in the instruction manual and a shorting cap for convenience in troubleshooting. Consult the manual for complete instructions and verify that the instrument operates as indicated and is stable in all steps.

Electrodes

1. Rinse electrode(s) thoroughly with distilled water.

2. Determine electrode slope. See Checking Electrode Operation.

3. If electrode fails this procedure, prepare electrode(s) as directed in Electrode Preparation. Clean electrode(s) as described in Electrode Maintenance.

4. Repeat step 2, Checking Electrode Operation.

5a.For the 94-16 Silver/Sulfide Half-Cell Electrode:

If the electrode(s) still do not perform as described, determine whether the silver/sulfide or reference electrode is at fault. To do this, substitute a known working electrode for the electrode in question and repeat the slope check.

5b.For the 96-16 Sure-Flow Combination Silver/Sulfide Electrode:

If the electrode still does not perform, replace the electrode.

6. If the stability and slope check out properly, but measurement problems persist, the sample may contain interferences or complexing agents, or the technique may be in error. See Standard, Sample, and Technique sections.

Page 58

7. Before replacing a “faulty” electrode, or if another electrode is not available for test purposes, review the instruction manual and be sure to:

– Clean the electrode thoroughly – Prepare the electrode properly – Use proper filling solution, ISA, SAOB II, and standards – Measure correctly – Review Troubleshooting Checklist

Standard

The quality of results depends greatly upon the quality of the standards. ALWAYS prepare fresh standards when problems arise – it could save hours of frustrating troubleshooting! Error may result from contamination of prepared standards, quality of distilled water, or a numerical error in calculating the concentrations.

The best method for preparation of standards is by serial dilution. This means that an initial standard is diluted, using volumetric glassware, to prepare a second standard solution. The second is similarly diluted to prepare a third standard, and so on, until the desired range of standards has been prepared.

Sample

If the electrodes work properly in standards but not in sample, look for possible interferences, complexing agents, or substances that could affect response or physically damage the sensing electrode or the reference electrode. If possible, determine the composition of the samples and check for problems. See Sample Requirements,

Interferences, and pH Requirements.

Technique

Check the method of analysis for compatibility with your sample. Direct measurement may not always be the method of choice. If a large amount of complexing agents is present, or if the sample has a high ionic strength, known addition may be best. If working at low levels, be sure to follow the low-level measurement technique. Also, be sure that the expected concentration of the ion of interest is within the electrode’s limits of detection. If problems persist, review operational procedures and instruction manuals to be sure that proper technique has been followed. Read Measuring Hints, Analytical Procedures and Electrode Characteristics.

Page 59

Assistance

After troubleshooting all components of your measurement system, contact The Technical Edge

for Orion products. Within the United

States call 1.800.225.1480, outside the United States call

978.232.6000 or fax 978.232.6031. In Europe, the Middle East and

Africa, contact your local authorized dealer. For the most current contact information, visit www.thermo.com

For the most current warranty information, visit www.thermo.com

Page 60

Figure 6 Typical Electrode Response

Reproducibility

Reproducibility is limited by factors such as temperature fluctuations, drift and noise. Within the electrode operating range, reproducibility is independent of concentration. With calibration every hour, direct electrode measurements reproducible to ± 2% (silver) or ± 4% (sulfide) can be obtained.

ELECTRODE CHARACTERISTICS

Electrode Response

The electrode potential plotted against silver concentration on semilogarithmic paper results in a straight line until concentration reaches 10

-6

M, with a slope of about (+) 54 to 60 mV per decade (see Figure 2). The potential plotted against sulfide concentration results in a straight line until concentration reaches 10-5M, with a slope of about (-) 25 to 30 mV per decade (see Figure 3). The electrode exhibits good time response (99% response to one minute or less) for concentrations above 10

-5

M. Below this value

response times vary from 2 to 5 minutes.

Electrode potential (mV)

440

280 240 200

time (minutes)

-3

M to 10

-5

M AgNO

10-3M to 10-4M AgNO

-3

M to 10

-2

M AgNO

320

400

480

360

Page 61

Temperature Effects

Since the electrode potentials are affected by changes in temperature, samples and standard solutions should be within ±1 °C (± 2 °F) of each other. At the 10

-3

M level, a 1 °C difference in temperature results in a 2% error (silver) or a 4% error (sulfide). The absolute potential of the reference electrode changes slowly with temperature because of the solubility equilibria on which the electrode depends. The slope of the electrode also varies with temperature, as indicated by the “S” in the Nernst equation, see Theory of Operation. Theoretical values of the slope at different temperatures are given in Table 8. If temperature changes occur, meter and electrodes should be recalibrated.

The electrode can be used at temperatures from 0 to 100 °C, provided that temperature equilibrium has occurred. For use at temperatures substantially different from room temperature, calibration standards should be at the same temperature as samples. The electrode should be used only intermittently at temperatures above 80 °C.

If sample temperatures vary, use of the 96-16 Sure-Flow Combination Silver/Sulfide Electrode is recommended. Optimum Results

™

A Filling Solution, when used for sulfide measurements, will minimize junction potentials and provide optimum temperature and time response. Optimum Results A produces an isopotential point of 3 x 10-5M S2-. Optimum Results C Filling Solution, when used for silver measurements, also provides optimum temperature and time response. Optimum Results C produces an isopotential point of 2 x 10

-3

M Ag+.

The isopotential point is the concentration at which the potential of the electrode does not vary with temperature. Since the isopotential point produced by both filling solutions is known, the Orion 96-16 may be used on meters that allow automatic temperature compensation for ISE, such as the Orion EA 940 and 920A. By programming in the isopotential point, and placing an ATC probe into the sample, any time the temperature changes, the meter will automatically adjust the slope of the calibration curve, resulting in more accurate measurement results.

Page 62

Table 8 Theoretical Values of Electrode Slope vs. Temperature

°C Slope (Ag+) Slope (S2-)

0 54.2 -27.1 10 56.2 -28.1 20 58.2 -29.1 25 59.2 -29.6 30 60.2 -30.1 40 62.2 -31.1 50 64.2 -32.1

Interferences

Mercury must be absent from all silver samples. Because of the extreme insolubility of HgS and Hg2S, mercury will not be present in any sulfide sample. Protein in food and biological samples interferes with silver measurements. Remove the protein interference by acidifying to pH 2-3 with 1 M HNO

. The sensing element is

oxidized by H202. If the electrode is exposed to high levels of interfering ions, it may

become unstable and sluggish in response. When this happens, restore normal performance by soaking for an hour in 0.2 M silver nitrate solution.

Page 63

pH Effects

In ammonia-free basic solutions, silver reacts with hydroxide ions to form a precipitate of Ag2O. This can be avoided by keeping solutions slightly acidic; use 1 M HNO

to adjust pH of silver

solutions below pH 8 if necessary. Hydrogen ion complexes sulfide ion to form bisulfide ion (HS

) and hydrogen sulfide (H2S). The lower the pH, the larger the amount of sulfide ion complexed. In acid solutions, sulfide is chiefly in the form of H

S. In the intermediate pH range (up to approximately pH 12) almost all the sulfide is in the form HS-. Only in very basic solutions does the sulfide exist primarily as free ion (S2-). Use of SAOB II in all samples and standards maintains a fixed level of S2-.

Complexation

For both silver and sulfide ions, the total concentration (Ct) consists of free ions (Cf) and bound or complexed ions in solution (Cb):

= Cf+ C

The electrode responds only to free ions so that any complexing agent in the solution reduces the measured concentration of silver or sulfide. Known addition is a recommended procedure for measuring silver in the presence of complexing agents.

Silver ions form complexes with a large number of species, including such common ones as EDTA and other chelating agents, ammonia, thiosulfate, and cyanide.

Sulfide forms complexes with hydrogen ion (HS

and H2S). In addition, sulfide ion forms soluble complexes with elemental sulfur (S

, S

, etc.), tin, antimony, and arsenic ions.

Page 64

Theory of Operation

The silver/sulfide electrode includes a silver/sulfide sensing element bonded into an epoxy body. When the sensing element is in contact with a solution containing either silver or sulfide ions an electrode potential develops across the sensing element. This potential, which depends on the level of free silver or sulfide ion in solution, is measured against a constant reference potential with a pH/mV meter or specific ion meter. The measured potential, corresponding to the level of silver or sulfide ion in solution, is described by the Nernst equation:

E= E

+ S log (A)

where: E = measured electrode potential

= reference potential (a constant) A = level of silver or sulfide ion in solution S = electrode slope (about 58 mV per decade for silver and

-28 mV per decade for sulfide)

S = 2.3 R T

where: R & F are constants

T = temperature degrees K n = ionic charge

The ionic level, A, is the activity or “effective concentration”. The silver or sulfide ion activity is related to free-ion concentration, C

by the activity coefficient, y:

A = y*C

Ionic activity coefficients are variable and largely depend on total ionic strength. The ionic strength of a solution is determined by all of the ions present. It is calculated by multiplying the concentration of each individual ion by the square of its charge, adding all these values up, and then dividing by two.

Ionic strength is defined as:

I= 1/2 ∑(C

iZi

)

where: C

= concentration of ion i Z

= charge of ion i S= symbolizes the sum of all the types of ions in solution.

Page 65

If the background ionic strength is high and constant relative to the ion concentration, the activity coefficient is constant and activity is directly proportional to concentration. Ionic strength adjustor (ISA) is added to all standards and samples so that the background ionic strength is high and constant relative to variable concentrations of silver. For silver, the recommended ISA is NaNO3. For sulfide, SAOB II is used to prevent oxidation and to free sulfide ion from hydrogen ion as well as to adjust the ionic strength. Other solutions can be used as long as they do not contain ions that would interfere with the electrode’s response to silver or sulfide. If samples have a high ionic strength (above 0.1 M), standards should be prepared with a composition similar to the samples.

Reference electrode conditions must also be considered. Liquidjunction potentials arise any time two solutions of different composition are brought into contact. The potential results from the interdiffusion of ions in the two solutions. Since ions diffuse at different rates, electrode charge will be carried unequally across the solution boundary resulting in a potential difference between the two solutions. In making electrode measurements, it is important that this potential be the same in the standardizing solution as in the sample solution; otherwise, the change in liquid-junction potential will appear as an error in the measured electrode potential.

Optimum Results

™

filling solutions are specifically designed to meet all reference electrode conditions. The filling solution is equitransferent. Therefore, the speed with which the positive and negative ions in the filling solution diffuse into the sample is as nearly equal as possible. If the rate at which positive and negative charge is carried into the sample solution is equal, then minimum junction potential can result.

Page 66

WARRANTY

For the most current warranty information, visit www.thermo.com. The Thermo Electron Corporation, Orion products warranty covers

failures due to manufacturer’s workmanship or material defects from the date of purchase by the user. User should return the warranty card and retain proof of purchase. Warranty is void if product has been abused, misused, or repairs attempted by unauthorized persons.

Warranties herein are for product sold/installed by Thermo or its authorized dealers.

Any product sold by a U.S. or Canadian distributor must be returned to Thermo for any warranty work. Please contact our Technical Service department for further information. A Return Authorization Number must be obtained from The Technical EDGE

For Orion Products before returning any product for in-warranty repair or replacement.

In the event of failure within the warranty period, Thermo will at the company’s option, repair or replace product not conforming to this warranty. There may be additional charges, including freight, for warranty service performed in some countries. For service, call Thermo or its authorized dealer outside the United States and Canada. Thermo reserves the right to ask for proof of purchase, such as the original invoice or packing slip.

Field Service is available on Orion BOD AutoEZ

™

, EZ Flash®GC Accessory and TEA Analyzer®. Contact our Field Service department for details on quotations, service, other field servicerelated activities.

The following products are warranted to be free from defects in material and workmanship in the period listed below from the date of purchase from the user or from the date of shipment from Thermo, whichever is earlier, provided use is in accordance with the operating limitations and maintenance procedures in the instruction manual and when not having been subjected to accident, alteration, misuse, abuse or breakage of electrodes:

Thirty-six months from date of purchase by the user (or forty-two months from date of shipment from Thermo)

• Waterproof Meters (Orion 630, 635, 830A, 835A, 260A, 261S,

265A, 266S, 130A, 131S, 135A, 136S, 1230, 142 and 842), Conductivity Meters (Orion 105Aplus

™

, 115Aplus™, 125Aplus™, 145Aplus™, 150Aplus™and 162A), PerpHect®pH/ISE Meters (Orion 310, 320, 330, 350, 370) pH/ISE Meters (Orion

Page 67

210Aplus™, 230Aplus™, 250Aplus™, 290Aplus™, 410Aplus™, 420Aplus™, 520Aplus™, 525Aplus™, 710Aplus™, 720Aplus™and 920Aplus™), pHuture MMS™Meters (Orion 535A and 555A), pH/Conductivity Meter (Orion 550A), Dissolved Oxygen Meters (Orion 805Aplus

™

, 810Aplus™, 850Aplus™and 862A).

Twenty-four months from date of purchase by the user (or thirtysix months from date of shipment from Thermo)

• Orion ROSS Ultra

Electrodes, AQUAfast®IV Colorimeters,

AQUAfast

IV Turbidimeter, Orion 925 Flash Titrator™, Series 100 DuraProbe™Conductivity Cells and Series 800 Dissolved Oxygen Probes.

Twelve months from date of purchase by the user (or eighteen months from date of shipment from Thermo)

• Laboratory pH Meters, (Orion 301, 611 and 940), SensorLink

pHuture

™

pH Meters (Orion 610 and 620), Smart Chek

™

meters, Sage®Pumps, Cahn®Balances, 930 Ionalyzer®, 950 ROSS™FAST QC™Titrator, 960 Titrator PLUS®, Karl Fischer Titrators, Autosamplers, Liquid Handling Devices, Liquid Handling Automation Workstations (Orion AS2000, AS2500 and AS4000), Pumps (Orion SP201, SP201-HR, SP201-S, Peristaltic and Rinse), pHuture

Conversion Box, Wine Master®, 607 Switchbox, rf link™, AQUAfast®II Colorimeters, Vacuum Degasser and Flowmeter.

• Orion EZ Flash

GC Accessory, Orion TEA Analyzer®610 and 510 excluding consumable items carry twelve months warranty only.

• Orion Ion Selective Electrodes, ionplus

Electrodes, ROSS

™

Electrodes, Sure-Flow®Electrodes, PerpHecT®Electrodes, AquaPro Professional Electrodes, No Cal™pH electrodes, Standard Line pH Electrodes, Tris pH Electrodes, KNIpHE

electrode, ORP Triode™(Orion 9180BN), pHuture™pH Probes (Orion 616500) and pHuture MMS™Quatrode™and Triode

™

(Orion 616600 and 617900), Orion 97-08 DO Probe, Series 100 Conventional Conductivity Cells, temperature probes and compensators (except those products noted).

• Orion 93 and 97 ionplus Series sensing modules are warranted to give six months of operation if placed in service before the date indicated on the package, except 93-07 and 97-07 Nitrate modules are warranted to give ninety days of operation if placed in service before the date indicated on the package.

Page 68

Six months from date of purchase by the user (or twelve months from date of shipment from Thermo)

• Orion Flash Titration

™

Probe (Orion 092518), pHuture

™

Electrode (Orion 615700), pHuture MMS™Pentrode™(Orion

617500), Quatrode™(Orion 617800) and Triode™(Orion

615800), Low Maintenance Triode™(Orion 9107BN), ORP Low Maintenance Triode™(Orion 9179BN), and PerpHecT®Low Maintenance Triode

™

(Orion 9207BN), Waterproof Triode

™

(Orion 9107WP, 9107WL, 9109WL and 9109WP), QuiKcheK

Meters and Micro Electrodes.

Three months from date of purchase by the user (or six months from date of shipment from Thermo)

• Economy Line Electrodes, Orion 91-05, 91-06, 91-15, 91-16, 91-25, 91-26, 91-35, 91-36, 92-06. Warranty also includes failure for any reason (excluding breakage), except abuse, provided the electrode is not used in solutions containing silver, sulfide, perchlorate, or hydrofluoric acid; or in solutions more than one (1) Molar in strong acid or base at temperatures above 50 °C.

“Out-of-Box” Warranty - Should any of the following products fail to work when first used, contact Thermo immediately for replacement.

• Orion Solutions, Standards, Reagents, Cables, Ferrules, Tubing, Line adapters, Printers, Software, Cases, Stands, Probe Membranes, AQUAfast

Test Strips, EZ Flash®columns, Liquid Handling Probes, Adapter Plates and Racks and general accessories.

For products in the catalog not listed in this warranty statement, please visit our website at: www.thermo.com

THE WARRANTIES DESCRIBED ABOVE ARE EXCLUSIVE AND IN LIEU OF ALL OTHER WARRANTIES WHETHER STATUTORY, EXPRESS OR IMPLIED INCLUDING, BUT NOT LIMITED TO, ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE AND ALL WARRANTIES ARISING FROM THE COURSE OF DEALING OR USAGE OF TRADE. THE BUYER’S SOLE AND EXCLUSIVE REMEDY IS FOR REPAIR OR REPLACEMENT OF THE NON-CONFORMING PRODUCT OR PART THEREOF, OR REFUND OF THE PURCHASE PRICE, BUT IN NO EVENT SHALL THERMO (ITS CONTRACTORS AND SUPPLIERS OF ANY TIER) BE LIABLE TO THE BUYER OR ANY PERSON FOR ANY SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL

Page 69

DAMAGES WHETHER THE CLAIMS ARE BASED IN CONTRACT, IN TORT (INCLUDING NEGLIGENCE), OR OTHERWISE WITH RESPECT TO OR ARISING OUT OF THE PRODUCT FURNISHED HEREUNDER.

REPRESENTATION AND WARRANTIES MADE BY ANY PERSON, INCLUDING ITS AUTHORIZED DEALERS, REPRESENTATIVES AND EMPLOYEES OF THERMO WHICH ALTER OR ARE IN ADDITION TO THE TERMS OF THIS WARRANTY SHALL NOT BE BINDING UPON THERMO UNLESS IN WRITING AND SIGNED BY ONE OF ITS OFFICERS.

Page 70

ORDERING INFORMATION

Orion Description

9416BN Silver/Sulfide Solid-State Epoxy Electrode,

BNC Connector

941600 Silver/Sulfide Solid-State Epoxy Electrode,

U.S. Std. Connector

9416SC Silver/Sulfide Solid-State Epoxy Electrode,

Screw Cap Connector. Requires separate cable

9616BN Sure-Flow

™

Silver/Sulfide Combination Solid-State

Epoxy Electrode, BNC Connector

961600 Sure-Flow Silver/Sulfide Combination Solid State

Epoxy Electrode, U.S. Std. Connector

900200 Double-Junction Sure-Flow Reference Electrode

900002 Double-Junction, Inner chamber Fill Solution,

5 x 60 mL bottle

900003 Double-Junction, Outer chamber Fill solution,

5 x 60 mL bottle

900067 Optimum Results

™

C Filling Solution for 96-16 Combination Silver/Sulfide Electrode, when used for silver measurements 5 x 60 mL bottle

900061 Optimum Results A Filling Solution for 96-16

Combination Silver/Sulfide Electrode, when used for sulfide measurements, 5 x 60 mL bottle

900062 Optimum Results B Filling Solution for 96-16

Combination Silver/Sulfide Electrode, for general measurements, 5 x 60 mL bottle

940011 ISA, 5M NaNO

, 475 mL

941609 Sulfide Anti-Oxidant Buffer (SAOB II) Reagent Pack

948206 Lead Perchlorate solution (0.1 M), 475 mL

984201 Polishing Strips, pk of twenty-four 6” strips.0

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SPECIFICATIONS

Concentration Range:

Silver : 10-7to 1 M (0.01 to 108,000 ppm) Sulfide: 10-7to 1 M (0.003 to 32,000 ppm)

pH Range:

2 to 12 pH units

Temperature Range:

0 to 80 °C continuous use 80 to 100 °C intermittent use

Electrode Resistance:

Less than 1 megohm

Reproducibility:

± 2% silver; ± 4% sulfide Size:

Length: 110 mm (excluding cap) Diameter: 9416 12 mm

9616 13 mm

Cap Diameter: 16 mm Cable Length: 1 M

Page 72

Environmental Instruments

Analyze •Detect•Measure •Control

™

227360-001 Rev. E

Water Analysis

North America

166 Cummings Center Beverly, MA 01915 USA Tel: 978-232-6000 Dom. Fax: 978-232-6015 Int’l. Fax: 978-232-6031

Europe

12-16 Sedgeway Business Park Witchford, Cambridgeshire England, CB6 2HY Tel: 44-1353-666111 Fax: 44-1353-666001

Far East

Room 904, Federal Building 369 Lockhart Road Wanchai, Hong Kong Tel: 852-2836-0981 Fax: 852-2834-5160

Customer Support

Toll Free: 800-225-1480 www.thermo.com Dom. e-mail: domcs1@thermoorion.com Int’l. e-mail: intcs1@thermoorion.com

For updated contact information, visit www.thermo.com

Thermo Scientific 9616BNWP Instruction Manual

Specifications and Main Features

Frequently Asked Questions

User Manual