Hanna Instruments HI 4101 User Manual

HI 4101

AMMONIA

Instruction Manual

HI 4101HI 4101

HI 4101

HI 4101HI 4101

Ammonia

Ion

Selective Electrode

HI 4101 Ammonia ElectrodeHI 4101 Ammonia Electrode

HI 4101 Ammonia Electrode

HI 4101 Ammonia ElectrodeHI 4101 Ammonia Electrode

I. I.

Introduction:Introduction:

Introduction:

I. I.

Introduction:Introduction: The Hanna HI 4101 Ammonia gas selective electrode is a combination electrode designed for the measurement of ammonia in aqueous solutions such as waste water samples, wine, beer. Ammonium ions are also measured by conversion to ammonia gas upon ISA addition.

II.II.

SpecificationsSpecifications

II.

Specifications

II.II.

SpecificationsSpecifications

Type: NH3 gas sensing

electrode with glass pH internal, Ag/ AgCl reference and gas permeable PTFE membrane.

Species Measured: NH

, NH

Measurement Range: 1.0 M to 1x 10-6M

17000 to 0.02 ppm

Interfering ions: Surfactants, wetting

agents, volatile amines. Operating Temperature: 0 to 40°C Operating pH: >11 pH Dimensions: 12 mm (OD) X 120

mm (insertion)

0.47”x 4.72”

Wetted materials: Delrin®, body and cap

PTFE gas membrane Connection: BNC

III.III.

Theory of OperationTheory of Operation

III.

Theory of Operation

III.III.

Theory of OperationTheory of Operation

:: The ammonia electrode is a complete potentiometric cell that contains both a silver/silver chloride (Ag/AgCl) reference and a pH measurement element. These elements are housed within a thermoplastic body in a chloride ion-containing electrolyte, and are isolated from the sample by a gas permeable membrane made of polytetrafluoroethylene (PTFE). Dissolved gas in the sample solution diffuses into the membrane and changes the pH in the thin film of electrolyte on the surface of the pH glass. Diffusion continues until the partial pressures of the gas in the sample and thin film are equal. The change in pH is proportional to the concentration of dissolved gas in the sample solution. The Nernst expression for an ammonia sensor is expressed in the equation below. Note that the potential is a function of the ammonia gas, which in turn is related to the hydroxyl ion concentration. The glass internal, Ag/AgCl reference, and Henry’s law constant are rolled into the E’ and E constants. The Nernst equation for the sensor becomes the equation noted below:

E = E’–2.3RT/nF log [A]= Eo–0.059 log [OH-]

E = observed potential E’ = Reference and fixed internal voltages R = gas constant (8.314 J/K Mol) n= Charge on ion (equivalents/mol) A

= ion activity in sample

ion

T = absolute temperature in K F = Faraday constant (9.648 x 104 C/equivalent)

The mV should decrease in a Nernstian manner as the ammonia partial pressure increases in the sample.

IV.IV.

Design ElementsDesign Elements

IV.

Design Elements

IV.IV.

Design ElementsDesign Elements The Hanna HI 4101 ammonia gas sensor has 3 main parts. These are the membrane/membrane cap, outer probe body with antirotation key and the pH/reference assembly which includes the outer electrode cap, spring, inner cap and pH/reference electrode assembly.

pH/reference electrode assembly

cable

outer electrode cap

spring

antirotation key inner cap

Outer probe body

reference electrode

pH sensitive

membrane

membrane/membrane cap

V.V.

Equipment Required:Equipment Required:

Equipment Required:

V.V.

Equipment Required:Equipment Required:

• Hanna HI 4222 pH/ISE/mV meter or other suitable ion or pH/mV meter. (Note: log/linear graph paper is useful if an ISE meter is not available).

• Hanna HI 180 magnetic stirrer or equivalent with stirring bars. (Note: Isolate beakers from stirrer motor heat by placing insulating material such as foam or cork between them).

• 2 or 3 necked flask with stoppers or

• Hanna HI 76404 electrode holder or equivalent with

Beakers or other suitable measurement vessel with plastic sealing film or wrap.

VI. VI.

Solutions Required for Calibration:Solutions Required for Calibration:

VI.

Solutions Required for Calibration:

VI. VI.

Solutions Required for Calibration:Solutions Required for Calibration:

Ionic Strength Adjuster (ISA): HI 4001-00 Hanna 0.1 M standard: HI 4001-01 Hanna 100 ppm N standard: HI 4001-02* Hanna 1000 ppm N standard: HI 4001-03* *Please Note: These calibration standards are ppm as NH3-N.

See Section XVII for additional solutions used for maintenance.

Using volumetric pipettes and glassware make dilutions of the standard to bracket the concentration of the samples. Standards with concentrations less than 10-3M should be prepared fresh daily. Store solution in a tightly sealed bottle without ISA added. 2 mL of HI 4001-00 ISA should be added to each 100 mL sample of standard and samples just prior to measurement. ISA adjusts the pH of the sample or standard to about pH 11 thus converting ammonium ion to ammonia. It also provides samples and standards a constant ionic strength background that stabilizes the solutions activity coefficient and permits concentration to be measured directly. The ISA provides color indication to verify it has been added to the solution and a complexing agent to remove metal ions (i.e copper, zinc) from solution. These

ions are capable of reducing the ammonia concentration. If other volumes of sample/standard are used, add ISA at 2 parts per 100 parts standard/sample.

VIIVII

General GuidelinesGeneral Guidelines

VII.

General Guidelines

VIIVII

General GuidelinesGeneral Guidelines

• Calibration standards and sample solutions should have the same ionic strength. ISA should be added to both samples and standards immediately before taking measurements.

• Calibration standards and sample solutions should be at the same temperature. Thermally insulate solution vessel from magnetic stirrer with cork or other insulating medium.

• Calibration standards and sample solutions should be stirred at the same rate using identical sized stir bars.

• Surface coating or “wetting“ the PTFE membrane will effect the response. Inspect sensor before using. Replace PTFE membrane if damage is evident.

• Rinse electrode with distilled or deionized water between samples and dab dry with lab wipe or other soft disposable absorbent toweling.

• Check calibration every 1-2 hours.

• Position sensors at an angle of approximately 20° to

lessen bubble adherence from solution out-gassing due to temperature change.

• Close container with plastic wrap or use

2 or 3 necked flask to prevent gas from leaving.

• Gently pulling cable will permit an exchange of fill solution at membrane surface. Re-Calibration is required.

VIII. VIII.

Inner Electrode CheckInner Electrode Check

VIII.

Inner Electrode Check

VIII. VIII.

Inner Electrode CheckInner Electrode Check

Before assembling the electrode for the

first timefirst time

first time or if

first timefirst time reactivating it after storage, the inner electrode assembly should be conditioned and then tested as a pH electrode.

Prepare pH test solutions HI 4000-47-4 and HI 4000-477 by mixing and dissolving each buffer packet in separate containers with 50 mL deionized water. These pH solutions contain chloride ions and pH buffers that are used to verify the inner electrode (pH internal) is operational. See Section XVII for replacement accessories and maintenance items. For a new sensor: Remove the protective shipping cap from the glass inner electrode.

Protective shipping cap

For existing sensor: Unscrew the upper cap on the top of the electrode and carefully withdraw the internal pH/reference assembly.

For stable readings, glass should be covered to the bottom of the long black band.

Use test tube or

Test buffer

can be

used as a

conditioning

solution

for the

pH internal

graduated cylinder (weighed Bottom) when testing or conditioning pH internal

• If sensor has been stored or shipped dry, it should be “conditioned” by soaking the pH/reference assembly 1 hour or more in one of the pH test solutions.

• Avoid touching the pH glass with your fingers.

• Attention: The pH/reference assembly is fragile!

Support the upper portion of the internal cell while

immersing the glass and reference assembly. A tall narrow container with weighted bottom is best. The pH test solution should cover the bottom of the large black ban.

Test: Connect the BNC connector on the electrode cable to a

pH/mV (mV or ORP mode) meter. Carefully immerse the sensor assembly into one of the buffers. When the measurment stabilizes record the mV generated. Rinse sensor tip in deionized water and dab dry between buffers to prevent solution carry-over. Do not rub the glass. Take a measurement in the second buffer and record mV. Pay attention to minus sign if present.

Calculate the difference in mV between the two solutions. Example of typical values:

HI 4000-47- 7 -90.2 mV HI 4000-47-4 80.66 mV

Difference 170.8 mV= 80.6-(-90.2) A calculated value equal or greater than 160 mV is acceptable for ambient temperatures between 20° and 25°C.

IX. IX.

Electrode PreparationElectrode Preparation

IX.

Electrode Preparation

IX. IX.

Electrode PreparationElectrode Preparation

1) Remove glass internal from sensor body and perform

inner electrode check. (See section VIII).

2) Install membrane on the outer probe body. Use twee-

zers provided and avoid touching working area of membrane with your fingers as skin oil will change the hydrophobic properties. Discard the paper backing (blue) found between white PTFE membranes. Hold membrane at corner with tweezers and drape over lower opening of outer probe body.

3) Hold one corner against the threads with thumb while gently stretching membrane over opening and capturing opposite membrane corner against threads . Smooth excess membrane material around the threads.

4) Screw outer membrane cap onto body thus capturing the membrane between the cap and outer body threads.

5.) Using dropper provided, add about 2 mL of ammonia internal electrolyte HI 4001-40 into outer probe body.

6) Insert and position the inner glass/reference assembly into the outer body so that the anti-rotation key sits in the cut out on the outer probe body.

HI 4101

IA N O M M A

HI 4101

IA N O M M A

7) Holding the electrode upright, slide spring and electrode cap down cable and screw cap on outer body until fully engaged. Do not invert electrode. Do not overtighten.

8) Install assembled electrode in gas sensor test vessel or in electrode holder and connect cable connector to pH/mV meter.

X. X.

Quick Check of Electrode SlopeQuick Check of Electrode Slope

Quick Check of Electrode Slope

X. X.

Quick Check of Electrode SlopeQuick Check of Electrode Slope

• Connect BNC (connector) to pH/mV/ISE meter.

• Place meter in mV mode.

• Place 100 mL of deionized water into a vessel with

stir bar. Add 2 mL of ISA Hanna HI 4001-00.

• Place sensor into prepared sample.

• Add 1 mL of 1000 ppm or 0.1 M Ammonia standard

to beaker. Record the mV value when stable.

• Add an additional 10 mL of standard to the solution. Record the mV when reading has stabilized. This value should be less than the previous noted (more negative).

• Determine the difference between the two mV values. An acceptable value for this slope is 54±4 mV at ambient temperatures between 20 and 25°C.

XI.XI.

Corrective actionCorrective action

XI.

Corrective action

XI.XI.

Corrective actionCorrective action

• Verify that the upper cap has been screwed in all the way.

• Verify electrode is connected properly to meter and the meter is is powered.

• Verify ISA has been added in the correct ratio to the standard.

• Examine the white membrane and check for electrolyte that might have leaked through the PTFE film. Replace membrane if damaged.

• If sensor does not change mV verify the the glass assembly is operational (See section VIII).

+ 28 hidden pages