Eutech Instruments AMMONIUM EPOXY User Manual

Instruction Manual Ammonium Electrode

EUTECH INSTRUMENTS PTE LTD.

AMMONIUM ION ELECTRODE

INSTRUCTION MANUAL

GENERAL INSTRUCTIONS

Eutech Instruments Ammonium Ion Electrode is used to measure ammonium ions in aqueous solutions in a more simple, quick, accurate, and economical manner.

Required Equipment

1. A pH/mV meter or an ion meter, either line operated or portable.

2. Semi-logarithmic 4-cycle graph paper for preparing calibration curves when using the

meter in the mV mode.

3. A magnetic stirrer.

4. Eutech Ammonium Ion Combination Epoxy-body Electrode, Code no. EC-NH4-03.

Required Solutions

1. Deionized or distilled water for solution and standard preparation.

2. Eutech Ionic Strength Adjuster (ISA), 5M NaCl, Code no. EC-ISA-AM1-BT to keep a constant background ionic strength present in the solution. To prepare the 5M NaCl ISA from your own laboratory stock, add 292 grams of reagent-grade sodium chloride (NaCl) to a 1,000 ml volumetric flask about half full of distilled water. Swirl the flask to dissolve the solid and fill to the mark with distilled water. Cap the flask and invert several times to mix the solution. Add 2 ml of ISA to every 100 ml of sample or standard solution for a background ionic strength of 0.10M.

3. Eutech Ammonium Standard, 0.1M NH4Cl, Code no. EC-SCS-AM1-BT. To prepare this standard, add 5.34 grams of reagent-grade ammonium chloride to a 1 liter volumetric flask about half full of distilled water. Swirl the flask to dissolve the solid and fill to the mark with distilled water. Cap the flask and invert several times to mix the solution.

4. Eutech Ammonium Standard, 1,000 ppm NH this standard, add 2.97 grams of reagent-grade ammonium chloride to a 1 liter volumetric flask about half full of distilled water. Swirl the flask to dissolve the solid and fill to the mark with distilled water. Cap the flask and invert several times to mix the solution.

, Code no. EC-SCS-AM2-BT. To prepare

Ammonium Electrode Instruction Manual

GENERAL PREPARATION

Electrode Preparation

Remove any rubber cap(s) covering the electrode tip(s) and the rubber inserts covering the filling holes of the reference electrode. Fill the combination electrode or the reference electrode with the filling solution shipped with the electrode to a level just below the fill hole. No preparation is required for a sealed reference electrode. Gently shake the electrode downward in the same manner as a clinical thermometer to remove any air bubbles that might be trapped behind the ammonium membrane. Prior to first usage, or after long term storage, immerse the ammonium electrode in ammonium standard for thirty minutes. The electrode is now ready for use. Connect the electrode(s) to the proper terminal(s) as recommended by the meter manufacturer.

Electrode Slope Check (with standard pH/mV meter)

(Check electrodes each day)

To a 150 ml beaker, add 100 ml of distilled water and 2 ml of ISA. Place the beaker on a magnetic stirrer and begin stirring at a constant rate. After assuring that the meter is in the mV mode, lower the electrode tip(s) into the solution.

Using a pipet, add 1 ml of 0.1M or 1,000 ppm ammonium standard to the beaker. When the reading is stable, record the millivolt reading. Using a pipet, add 10 ml of the standard used above to the beaker. When the reading has stabilized, record the millivolt reading.

Determine the difference between the two readings. A difference of 56±2 mV indicates correct electrode operation, assuming the solution temperature is between 20o and 25oC. See the

TROUBLESHOOTING section if the potential change is not within this range.

Slope is defined as the change in potential observed when the concentration changes by a factor of

10.

Electrode Slope Check (with ion meter)

(Check electrodes each day)

Prepare standard ammonium solutions whose concentrations vary by tenfold. Use either the 0.1M

or the 1,000 ppm NH

standard stock solutions. Use the serial dilution method for this

preparation.

To a 150 ml beaker, add 100 ml of the lower value standard and 2 ml of ISA. Place the beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tip(s) into the solution.

Assure that the meter is in the concentration mode. Adjust the meter to the concentration of the standard and fix the value in the memory according to the meter manufacturer's instructions.

Rinse the electrode(s) with distilled water and blot dry. To a 150 ml beaker, add 100 ml of the higher value standard and 2 ml of ISA. Place the beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tip(s) into the solution.

Adjust the meter to the concentration of the standard and fix the value in the memory. Read the electrode slope according to the meter manufacturer's instructions. Correct electrode operation is

Instruction Manual Ammonium Electrode

indicated by a slope of 90-100%. See the TROUBLESHOOTING section if the slope is not within this range.

MEASUREMENT

Measuring Hints

The sensing membrane is normally subject to water uptake and might appear milky. This has no effect on performance. All samples and standards should be at the same temperature for precise measurement, preferably ambient temperature.

Constant, but not violent, stirring is necessary for accurate measurement. Magnetic stirrers can generate sufficient heat to change the solution temperature. To counteract this effect, place a piece of insulating material, such as styrofoam sheet or asbestos sheet, between the stirrer and beaker.

Always rinse the electrode tip(s) with distilled water and blot dry with a fresh tissue between readings to prevent solution carryover.

Check the electrode for air bubbles adhering to the membrane surface after immersion in solution. Agitate the electrode gently to remove the air bubbles.

A slow or sluggish electrode response may indicate surface contamination of the ammonium electrode membrane. Soak the electrode tip in distilled water for about 5 minutes to clean the membrane. Rinse the membrane and soak in diluted standard solution for about 5 minutes to restore performance.

When measuring samples with high ionic strength, prepare standards with compositions similar to that of the sample.

Dilute concentrated samples (over 0.1M) before measurement. Recalibrate every few hours for routine measurement.

Sample Requirements

Make sure that the samples and standards are at the same temperature. About a 2% error will be introduced for a 1oC difference in temperature. Temperature should normally be less than 40oC with intermittent measurements allowed to 50oC. All samples and standards must be aqueous. They must not contain organic solvents.

Interference found in Table 3 should be absent.

Units of Measurement

Ammonium concentrations are measured in units of parts per million as ammonium, parts per million as N, moles per liter, or any other convenient concentration unit. Table 1 indicates some of the concentration units.

Ammonium Electrode Instruction Manual

TABLE 1: Concentration Unit Conversion Factors

ppm NH

ppm N moles/liter NH

1.80 1.40 1x10-4

18.00 14.00 1x10-3

180.00 140.00 1x10-2

Measurement Procedure

Direct Measurement

A simple procedure for measuring a large number of samples. A single meter reading is all that is required for each sample. The ionic strength of samples and standards should be made the same by adjustment with ISA for all ammonium samples. The temperature of both sample solution and of standard solutions should be the same.

Direct Measurement of Ammonium (using a standard pH/mV meter)

1. Prepare 10

, 10

, and 10

M or 100, 10, and 1 ppm standards by serial dilution of the

0.1M or 1,000 ppm standard. Add 2 ml of ISA per 100 ml of standard.

2. Place the most dilute solution (10

M or 1 ppm) on the magnetic stirrer and begin stirring at a constant rate. After assuring that the meter is in the mV mode, lower the electrode tip(s) into the solution. When the reading has stabilized, record the mV reading.

3. Place the midrange solution (10

M or 10 ppm) on the magnetic stirrer and begin stirring. After rinsing the electrode(s) with distilled water and blotting dry, immerse the electrode tip(s) in the solution. When the reading has stabilized, record the mV reading.

4. Place the most concentrated solution (10

M or 100 ppm) on the magnetic stirrer and begin stirring. After rinsing the electrode(s) with distilled water and blotting dry, immerse the electrode tip(s) in the solution. When the reading has stabilized, record the mV reading.

5. Using the semi-logarithmic graph paper, plot the mV reading (linear axis) against the concentration (log axis). A typical calibration curve can be found in Figure 1.

Instruction Manual Ammonium Electrode

A calibration curve is constructed on semi-logarithmic paper when using a pH/mV meter in the direct measurement procedure. The measured electrode potential in mV (linear axis) is plotted against the standard concentration (log axis). In the linear region of the curve, only three standards are necessary to determine a calibration curve. In the non-linear region, additional points must be measured. The direct measurement procedures given are for the linear portion of the curve. The non-linear portion of the curve requires the use of low level

procedures. Extrapolate the curve down to about 1x10

M or 0.2 ppm.

6. To a clean, dry 150 ml beaker, add 100 ml of sample and 2 ml of ISA. Place the beaker on the magnetic stirrer and begin stirring. Place the electrode tip(s) in the solution. When the reading has stabilized, record the millivolt reading. Determine the concentration directly from the calibration curve.

7. The electrode(s) should be re-calibrated every 1-2 hours. Simply repeat Steps 2-5 above.

Direct Measurement of Ammonium (using an ion meter)

1. By serial dilution of the 0.1M or 1,000 ppm ammonium standard, prepare two ammonium

standards whose concentration is near the expected sample concentration. Measure out 100 ml of each standard into individual 150 ml beakers and add 2 ml of ISA to each.

2. Place the more dilute solution on the magnetic stirrer and begin stirring at a constant rate.

Assure that the meter is in the concentration mode.

3. Lower the electrode tip(s) into the solution.

4. Adjust the meter to the concentration of the ammonium standard and fix the value in the

memory according to the meter manufacturer's instructions after stabilization of the reading.

5. Rinse the electrode tip(s) with distilled water and blot dry.

6. Place the more concentrated solution on the magnetic stirrer and begin stirring at a

constant rate.

7. Lower the electrode tip(s) into the solution.

8. Adjust the meter to the concentration of the ammonium standard and fix the value in the

memory according to the meter manufacturer's instructions after stabilization of the reading.

9. For low level measurements, place the rinsed, dried electrode(s) into a solution containing

100 ml of distilled water and 2 ml of ISA. After stabilization, fix the blank value in the meter according to the meter manufacturer's instructions.

10. Place 100 ml of the sample and 2 ml of ISA in a 150 ml beaker, place it on the magnetic

stirrer, and begin stirring.

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