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Ion-Selective Electrode for silver ion (ELIT 8211 crystal membrane)
Reference electrode: double junction lithium acetate (ELIT 003n)
Dual electrode head (ELIT 201)
Standard solution: 1000 ppm Ag as AgNO3
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, 1, and 0.1ppm Ag. However, this wide calibration is not necessary if the approximate range of concentrations of the samples is known, and this is within the linear range of the ISE. In this case it is only necessary to make two solutions (preferably a decade apart) which span the sample range.
After dilution, the standard solutions should be mixed with buffer solution in the ratio 50:1 and measured whilst stirring.
Follow the instructions in the General Operating Instructions to measure these standard solutions and prepare a calibration graph.
Samples must also be mixed 50:1 with buffer solution and stirred well before 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 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.
Chemical / Operational