Ion-Selective Electrode for Nitrite ion (detectION 3071 is recommended)
pH/Ion meter with a ISE (or Concentration mode) with
Standard solution: NaNO2, 1000 ppm as NO2 (this reagent has short shelf-life due to oxidation)
Buffer solution (ISAB): Citric (This is a solution containing 14.32g Bisodium phosphate, and 15.37g Citric acid dissolved in 1000ml water).
All standards and samples must be mixed with this buffer in a ratio of 1:1.
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 NO2. Mix 10 ml of standard with 10 ml of buffer solution before analysis. All standard solutions good for one day only.
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, 3 and 13ppm then you could use standards of 1 and 100ppm or achieve even better accuracy making, say, 2 and 15ppm standards.
Mix 10ml of sample with 10ml of buffer solution before analysis.
Follow the instructions on your pH/ Ion Meter 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
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.