Thermo Scientific 9616BNWP Instruction Manual

Analyze •Detect•Measure •Control

™

Orion 94-16
Orion 96-16 ionplus

Orion Silver/Sulfide

Electrode

INSTRUCTION MANUAL

Ag

/S

+

-

2

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Electron Corporation.

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

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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

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.

1

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.

2

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

3

Prepared
(see below)

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

3

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

2-

Prepared
(see below)

3

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

3

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.

4

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

2

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.

5

6

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.

7

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

Ag

+

and S

2-

Constant sample

temperature

Low-level silver

measurement

Cyanide indicator method

Optimum
Results C 900067 Silver measurements

Variable sample

temperatures

8

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.

9

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.

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

2-

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

3

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

2

S, no dissolved mercury

ions will be present in sulfide samples.

10

11

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.

12

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

1

2

3

4

5
6

Figure 1 GLP Measuring Hints

13

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.

14

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.

15

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.

16

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.

17

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

10

-5

11010210

3

10

4

Molarity

ppm silver

10

-4

10

-3

10

-2

10

-1

500.0

Electrode potential
(mV)

57 mV

10-fold change

18

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.