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Method for determining PERCHLORATE (ClO4-)
in Aqueous Solutions

Electrode Specifications       Links to publications on the WWW     Go to Ion Selective Electrodes page

Apparatus Required:

Ion-Selective Electrode for perchlorate ion (ELIT 8061 PVC membrane)

Reference electrode: single junction silver chloride (ELIT 001n)

Dual electrode head (ELIT 201)

Standard solution: 1000 ppm ClO4 as NaClO4

Buffer solution (ISAB): 1 Molar CH3COONa .

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

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, 1, and 0.1ppm ClO4. If the approximate range of concentrations of the samples is known, and this is within the linear range of the ISE, then it is only necessary to make two solutions (preferably one decade apart) which span this range:.

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 in the General Operating Instructions to measure these standard solutions and prepare a calibration graph.

Sample Preparation:

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.

Sample Measurement:

Follow the instructions in the 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.

Technical Specifications
for the Perchlorate Ion-Selective Electrode
(ELIT 8061)

Click here to download a printer-friendly (pdf) Specification Sheet.

The Perchlorate Ion-Selective Electrode has a solid-state PVC polymer matrix membrane. The electrode is designed for the detection of perchlorate ions (ClO4- ) in aqueous solutions and is suitable for use in both field and laboratory applications.
The Perchlorate Ion is a monovalent anion.
One mole of ( ClO4-) has a mass of 99.451 grams; 1000 ppm is 0.010 M
Dissolve 1.231g anhydrous sodium perchlorate (NaClO4) in 1 litre water.

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 25C < 2.5 MOhm
Minimum feasible sample volume = 5 ml

Chemical / Operational Specifications
Preconditioning / Standard solution : Normally 1000 ppm ClO4- as NaClO4
(But see General Operating Instructions)
Preconditioning time : at least 5 minutes
Optimum pH range : pH 0 to pH 11
Temperature range : 0 to 50C
Recommended ISAB : 1M CH3COONa (Add 2% v/v)
Recommended reference electrode : Single junction (ELIT 001)
Electrode slope at 25C : 54 5 mV/decade
Concentration range : 0.2 to 9,960 ppm (2x10-6 to 0.1 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.

The following ions interfere with the perchlorate electrode (selectivity coefficients in brackets) Thiocyanate (0.03), Iodide (0.02), Nitrate (0.02), Chloride (0.0003), Phosphate (0.0002), Acetate (0.0001).
The SC is the approximate apparent  increase in the measured concentration caused by 1 unit of the interferent.  Thus the likely effect of any interfering ion (% increase) can be calculated as follows: 
((expected concentration) x (SC) / (expected ClO4 concentration)) x 100.

Thus nitrate can be tolerated up to the same concentration as perchlorate (this will cause an approximately 2% enhancement), and chloride can be present up to 100 times more concentrated before it will cause a significant error.

Return to top           Last Update: CCR 18 Feb 2015