Introduction
The Chloride Ion-Selective Electrode has a solid-state poly-crystalline membrane. The electrode is designed for the detection of chloride ions (Cl^- ) in aqueous solutions and is suitable for use in both field and laboratory applications.
The Chloride Ion is a monovalent anion .
One mole of ( Cl-) has a mass of 35.453 grams; 1000 ppm is 0.028M

Physical Specifications
Length of body excluding gold contact = 130 mm
Length of body including gold contact = 140 mm
Diameter of body = 8 mm
DC resistance at 25° C < 0.5 MOhm
Minimum feasible sample volume = 5 ml

Chemical / Operational Specifications
Preconditioning / standard solution : Normally 1000 ppm Cl- as NaCl
(But see General Operating Instructions)
Preconditioning time : 5 minutes
Optimum pH range : pH 1 to pH 12
Temperature range : 5°C to 80°C
Optimum temperature : 25°C
Recommended ISAB : 5M NaNO3 (Add 2% v/v)
Recommended reference electrode : Double junction (ELIT 002 or 003)
Reference electrode outer filling solution : 0.1M KNO3 or 0.1M CH3COOLi
Electrode slope at 25°C : 54 ± 5 mV/decade
Concentration range : 1 to 35,000 ppm (3x10-5 to 1 Molar)
Response time : < 10 seconds
Defined as time to complete 90% of the change in potential after immersion in the new solution.
Time for stable reading after immersion : < 1 to > 5 minutes
Depending on concentration, use of ISAB, nature of sample and stabilisation time of liquid junction potential of reference electrode.
Potential drift (in 1000 ppm) : < 3 mV/day (8 hours)
Measured at constant temperature and with ISE and Reference Electrode continually immersed.

Interference:
NB: Because of the much greater solubility of AgCl compared to AgI, the Chloride electrode will be irreversibly damaged if immersed in solutions containing significant numbers of Iodide ions.Also note that all poly-crystalline membranes contain Silver Sulphide and thus will not give reliable readings if more than a trace of Ag or S ions are present in the solution. There is also a high interference from Bromide and Cyanide ions and the Chloride electrode will only give reliable results if these ions are absent, or only present in insignificant amounts compared to the Chloride ion.

If samples are likely to contain significant quantities of these ions, then their effect may be reduced by mixing samples and standards 1:1 with a sodium bromate buffer. This is made by dissolving 15.1 g sodium bromate in 800 ml water and addding 75ml of concentrated nitric acid. This must be stirred well and diluted to 1000 ml with water. Note that this is a strong oxidising solution which should be handled carefully and prepared and used in a well ventilated area since it may liberate Bromine gas. This buffer should remove up to 1000ppm of Bromide or Iodide and 500ppm Sulphide. Small quantities of Cyanide should also be oxidised - but this acid solution must not be added to samples with significant cyanide content because of the danger of liberating lethal HCN gas.

Ion-Selective Electrode for chloride ion (ELIT 8261 crystal membrane)

Reference electrode: double junction potassium nitrate (ELIT 002)

Dual electrode head (ELIT 201)

Standard solution: 1000 ppm Cl as KCl

Buffer solution (ISAB): 5 Molar NaNO₃.

ELIT Computer Interface/Ion Analyser, or Ion/pH/mV meter.

100 or 150 ml polypropylene beakers, 100ml volumetric flask, 1, 2, 5, 10ml pipettes.

Before use, the electrodes must be calibrated by measuring a series of known standard solutions, made by serial dilution of the 1000ppm standard solution. For a full calibration, prepare 100ml of solutions containing 1000, 100, 10, 1ppm Cl. If the approximate range of concentrations of the samples is known, and this is within the specified linear range of the ISE, then it is only necessary to make two solutions which span this range: e.g. if samples are known to lie between, say, 30 and 130ppm then you could use standards of 10 and 200ppm or even 20 and 150ppm.

NB: If the samples to be measured are expected to have a total ionic strength of greater than 0.01 Molar, then 2 ml of buffer solution should be added to each 100ml standard and mixed thoroughly to compensate for different activity coefficients between samples and standards.

Follow the instructions on the computer interface software to measure these standard solutions and prepare a calibration graph.

For low ionic strength samples, no sample preparation is necessary. Simply take approximately 50 to 100 mls of sample in a plastic beaker, or even immerse the electrodes directly in a lake or river (but take care to avoid losing the electrodes!). For samples with high ionic strength, take 100mls of sample and add 2 mls of buffer solution and stir well before measurement.

Follow the instructions in the computer interface software and/or electrode operating instructions to measure a series of samples and record the results. Briefly, it is important to note that, if measuring in beakers, the electrodes must be washed and dried between each sample, to avoid cross contamination, and sufficient time must be allowed (2 or 3 minutes), before taking a reading after immersion, to permit the electrode signal to reach a stable value. For the highest precision, frequent recalibration is recommended (see operating instructions).

The results will be displayed as ppm and mol/l. If buffer solution has been added equally to standards and samples then these figures will not need adjusting because they will all be affected by the same dilution factor.

The casein in milk tends to clog the ion selective membrane and thus reduce its sensitivity. This problem can be overcome by mixing one volume of milk sample with two volumes of dilute nitric acid (60 ml concentrated HNO₃ diluted to 1 litre with de-ionised water) and shaking for one minute. The nitric acid is used instead of NaNO₃ ISAB and must be added to all standards in the same proportion as the samples. After mixing with the nitric acid, samples are measured in the conventional manner.

Ion-Selective Electrode for chloride ion (ELIT 8261 crystal membrane)

Reference electrode: double junction potassium nitrate (ELIT 002)

Dual electrode head (ELIT 201)

Standard solution: 1000 ppm Cl as KCl

Buffer solution (ISAB): Dilute Nitric Acid.

ELIT Computer Interface/Ion Analyser, or Ion/pH/mV meter.

100 or 150 ml polypropylene beakers, 100ml volumetric flask, 1, 2, 5, 10, 25ml pipettes.

Before use, the electrodes must be calibrated by measuring a series of known standard solutions, made by serial dilution of the 1000ppm standard solution. For a full calibration, prepare 100ml of solutions containing 1000, 100, 10, 1ppm Cl. If the approximate range of concentrations of the samples is known, and this is within the specified linear range of the ISE, then it is only necessary to make two solutions which span this range: e.g. if samples are known to lie between, say, 30 and 130ppm then you could use standards of 10 and 200ppm or even 20 and 150ppm.

Mix the standards with nitric acid ISAB in the proportion 1:2.

Follow the instructions on the computer interface software to measure these standard solutions and prepare a calibration graph.

Take 50ml of milk sample and mix thoroughly for at least 1 minute with 100ml of dilute nitric acid before measurement.

Follow the instructions in the computer interface software and/or electrode operating instructions to measure a series of samples and record the results. Briefly, it is important to note that the electrodes must be washed and dried between each sample, to avoid cross contamination, and sufficient time must be allowed (2 or 3 minutes), before taking a reading after immersion, to permit the electrode signal to reach a stable value. For the highest precision, frequent recalibration is recommended (see operating instructions).

The results will be displayed as ppm and mol/l. If buffer solution has been added equally to standards and samples then these figures will not need adjusting because they will all be affected by the same dilution factor.

To measure chloride in meat samples it is necessary to use 0.5M nitric acid as ISAB (made by diluting 31.25ml conc. HNO3 to 1 litre) and add this in the proportion 1:1 to all samples and standards. Chloride is extracted from meat products by liquidising 1g of meat with 100 ml of water. After filtration, 25 ml of the sample solution is mixed with 25 ml of ISAB and analysed as normal. The measured sample concentration must be multiplied by 100 to obtain the concentration in micrograms per gram of meat.

Ion-Selective Electrode for chloride ion (ELIT 8261 crystal membrane)

Reference electrode: double junction potassium nitrate (ELIT 002)

Dual electrode head (ELIT 201)

Standard solution: 1000 ppm Cl as KCl

Buffer solution (ISAB): 0.5 Molar nitric acid.

ELIT Computer Interface/Ion Analyser, or Ion/pH/mV meter.

100 or 150 ml polypropylene beakers, 100ml volumetric flask, 1, 2, 5, 10, 25 ml pipettes.

Before use, the electrodes must be calibrated by measuring a series of known standard solutions, made by serial dilution of the 1000ppm standard solution. For a full calibration, prepare 100ml of solutions containing 1000, 100, 10, 1ppm Cl. If the approximate range of concentrations of the samples is known, and this is within the specified linear range of the ISE, then it is only necessary to make two solutions which span this range: e.g. if samples are known to lie between, say, 30 and 130ppm then you could use standards of 10 and 200ppm or even 20 and 150ppm.

Before measuring, each standard must be mixed 1:1 with ISAB.

Follow the instructions on the computer interface software to measure these standard solutions and prepare a calibration graph.

After filtration, take 25ml of each sample and mix with 25 ml of 0.5 Molar nitric acid ISAB.

Follow the instructions in the computer interface software and/or electrode operating instructions to measure a series of samples and record the results. Briefly, it is important to note that, if measuring in beakers, the electrodes must be washed and dried between each sample, to avoid cross contamination, and sufficient time must be allowed (2 or 3 minutes), before taking a reading after immersion, to permit the electrode signal to reach a stable value. For the highest precision, frequent recalibration is recommended (see operating instructions).

The results will be displayed as ppm and mol/l. Since buffer solution has been added equally to standards and samples then these figures will not need adjusting because they will all be affected by the same dilution factor, but the ppm concentration in the solution will have to be multiplied by 100 to get the concentration in the meat in micrograms per gram (mg/Kg

Chloride is extracted from butter by heating with dilute nitric acid and measured by direct potentiometry.

Ion-Selective Electrode for chloride ion (ELIT 8261 – crystal membrane)

Reference electrode: double junction potassium nitrate (ELIT 002)

Dual electrode head (ELIT 201)

Standard solution: 1000 ppm Cl as KCl

Buffer solution (ISAB): Dil. nitric acid (dilute 60ml conc. HNO3 to 1 litre).

ELIT Computer Interface/Ion Analyser, or Ion/pH/mV meter.

100 or 150 ml polypropylene beakers, 100ml volumetric flask, 1, 2, 5, 10, 25 ml pipettes.

Before use, the electrodes must be calibrated by measuring a series of known standard solutions, made by serial dilution of the 1000ppm standard solution. For a full calibration, prepare 100ml of solutions containing 1000, 100, 10, 1ppm Cl. If the approximate range of concentrations of the samples is known, and this is within the specified linear range of the ISE, then it is only necessary to make two solutions which span this range: e.g. if samples are known to lie between, say, 30 and 130ppm then you could use standards of 10 and 200ppm or even 20 and 150ppm.

Before measuring, each standard must be mixed 1:1 with dil. HNO3 ISAB.

Follow the instructions on the computer interface software to measure these standard solutions and prepare a calibration graph.

1) Weigh accurately about 10g of butter and place in a beaker with 100ml dil HNO3.

Follow the instructions in the computer interface software and/or electrode operating instructions to measure a series of samples and record the results. Briefly, it is important to note that, if measuring in beakers, the electrodes must be washed and dried between each sample, to avoid cross contamination, and sufficient time must be allowed (2 or 3 minutes), before taking a reading after immersion, to permit the electrode signal to reach a stable value. For the highest precision, frequent recalibration is recommended (see operating instructions).

The results will be displayed as ppm and mol/l in the solution. Since buffer solution has been added equally to standards and samples then these figures will not need adjusting because they will all be affected by the same dilution factor. The ppm concentration in the solution will have to be multiplied by 100 and divided by the sample weight to get the concentration in the butter in micrograms per gram (= ppm = mg/Kg)

Because of the complex matrix, high ionic strength, and other interfering factors in fruit juice, the concentration of ions in the solution is best determined using the Sample Addition method rather than direct potentiometry.

Ion-Selective Electrode for chloride ion (ELIT 8261 – crystal membrane)

Reference electrode: double junction potassium nitrate (ELIT 002)

Dual electrode head (ELIT 201)

Standard solution: 1000 ppm Cl as KCl

ELIT Computer Interface/Ion Analyser, or Ion/pH/mV meter.

100 or 150 ml polypropylene beakers, 100ml volumetric flask, 1, 2, 5, 10ml pipettes.

Before use, the electrodes must be calibrated to find an accurate value for the slope under the current operating conditions and in the range of the expected sample concentrations. If sample concentration is completely unknown then it is best to make a quick sample measurement first, using direct potentiometry with an old calibration. Then make up and measure two standards which span the expected sample range - say 1 & 10ppm or 10 & 100ppm - or more closely spaced if working below the linear range of the electrode.

1) Pipette the pre-determined standard volume (usually 50 or 100ml) into a beaker, immerse the electrodes, swirl the solution, and record the stable voltage after a few minutes of stabilization.

2) Add the calculated volume of sample, swirl or stirr well then wait for a new stable voltage when the solutions have completely mixed and the electrodes have re-equilibrated.

The software will then calculate the sample concentration and give an estimate of the quality of the determination - if the sample concentration is very different from the expected value then you will be prompted to make a second measurement using a more appropriate volume or concentration of standard or volume of sample.