Introduction
The Thiocyanate Ion-Selective Electrode has a solid-state crystal membrane. The electrode is designed for the detection of thiocyanate ions (SCN^- ) in aqueous solutions and is suitable for use in both field and laboratory applications.  The Thiocyanate Ion is a monovalent anion.
One mole of SCN- has a mass of 58.1 grams; 1000 ppm is 0.017M

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 < 2.5 MOhm
Minimum feasible sample volume = 5 ml

Chemical Specifications
Preconditioning / Standard solution : Normally 1000 ppm SCN- as KSCN
(But see General Operating Instructions)
Preconditioning time : 5 minutes
Optimum pH range : pH 2 to pH 12
Temperature range : 5°C to 80°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 5,800 ppm (2x10-5 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.

Interference:
NB: All poly-crystalline membranes contain Silver Sulphide and thus will not give reliable readings if Ag or S ions are present in the solution. Chloride, Bromode and Iodide have very high interference and must be absent, or only present in very low concentrations relative to the SCN. There is also a small interference from thiosulphate ions (S2O3--)

Procedure for determining the concentration of THIOCYANATE (SCN^-) in WATER

Ion-Selective Electrode for thiocyanate ion (ELIT 8229 crystal membrane)

Reference electrode: double junction potassium nitrate (ELIT 002).

Dual electrode head (ELIT 201)

Standard solution: 1000 ppm SCN^- as KSCN

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, and 1ppm SCN. 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.