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Ion-Selective Electrode for cupric ion (ELIT 8227 crystal membrane)
Reference electrode: double junction Lithium Acetate (ELIT 003n).
Dual electrode head (ELIT 201)
Standard solution: 1000 ppm Cu as CuSO4
Buffer solution (ISAB): 5 Molar NaNO3.
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, and 1 ppm Cu. 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 a decade apart) which span this range.
NB: The Cu electrode works most reliably when samples and standards are mixed with ISAB to give a background matrix of around 0.1 Molar NaNO3. Thus 2 ml of buffer solution should be added to each 100ml standard (and sample) solution and mixed thoroughly before measurement.
Follow the instructions in the General Operating Instructions to measure these standard solutions and prepare a calibration graph.
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 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, these figures will not need adjusting for this extra dilution factor.
Chemical / Operational
Bromide and Chloride ions both have selectivity coefficients of >1 and will cause a significant negative error it they are present in concentrations greater than one tenth of that of the Copper.
Return to top Last update: CCR 14 August 2015