What is a suitable reference electrode for ISE half cells?
A double junction Ag/AgCl reference electrode with a replaceable outer electrolyte can be used in most instances, such as the Ionode IJ14 Intermediate junction reference electrode.
How do I easily check the response of an ISE?
A simple procedure is to make up a 100mL 1ppm solution of the ion to be tested. Observe the potential, and then add 10mL of 100ppm standard to this solution. Observe this potential. The potential difference for monovalent ions should be at least 55mV at 25oC (27mV for divalent ions).
What is a suitable reference electrolyte for use in the Ionode Cyanide combination ISE?
Since the determination of Cyanide is performed in alkaline conditions, better results may be obtained by using a mixture of dilute (~0.1M) Potassium Hydroxide with 1M Potassium Nitrate.
What is a suitable reference electrolyte for use in the Ionode Chloride, Bromide, Iodide, or Fluoride combination ISEs?
A suitable electrolyte is 1M Potassium Nitrate, available as KN45.
What about interferences?
Interferences for Ion selective electrodes will be listed in the user manual. In most cases, these can be minimized. Techniques such as standard addition may need to be used in some circumstances.
What are some basic recommendations to obtain accurate ISE measurements?
Calibrate and measure at the same temperature; use the same stirring speed in calibration and measurements; calibrate from the lowest concentration to the highest; use ISA; and use AR grade reagents.
What are the Basic Requirements needed to Perform ISE measurements?
Your will require a pH/mV meter(with 0.1mV resolution), or an Ion meter, a stirred electrode stand, Ion selective electrode (and separate reference, if not using a combination electrode), temperature sensor, analytical grade reagents for ISA and calibration, and volumetric glassware.
What is the Purpose of ISA (ionic strength adjuster)?
Unlike pH buffers, the ionic strength of ion solutions varies with the concentration of the ion to be measured. To maintain a constant ionic strength, a neutral salt is added, such that the total ionic strength is independent of the analyte concentration. In the example of chloride measurement, an ISA made from potassium nitrate is suitable; add this to the standards and samples so that the concentration "in the beaker" is around 0.1-0.4M. ISA's can also be used to adjust the pH and to complex/precipitate undesired interferences; a good example is TISAB, which is used for Fluoride determination.