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Chemical / Operational
Recommended reference electrode : Single Junction AgCl (ELIT 001)
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Procedure for determining the concentration of SODIUM (Na+) in WATER
Ion-Selective Electrode for sodium ion (ELIT 8230 PVC membrane)
Reference electrode: double junction lithium acetate (ELIT 003)
Dual electrode head (ELIT 201)
Standard solution: 1000 ppm Na as NaCl
Buffer solution (ISAB): None suitable.
ELIT Computer Interface/Ion Analyser, or Ion/pH/mV meter.
100 or 150 ml polypropylene beakers, 100ml volumetric flask, 1, 2, 5, 10ml pipettes.
Analysis of low ionic strength samples using Direct Potentiometry
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 Na. 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.
Follow the instructions in the General Operating Instructions to measure these standard solutions and prepare a calibration graph.
No sample preparation necessary. Simply immerse the electrodes in a sample to a depth of a few millimetres.
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).
Analysis of high ionic strength samples(>0.01Molar) using Standard Addition Method.
The Standard Addition method involves measuring the electrode potential in a known volume of sample (say 100ml) and then adding a smaller volume of standard (say 2ml), mixing well and measuring a second potential. Details of this method are given in the general electrode operating instructions. Measurement and calculations are made very easily using the ELIT two-channel electrode-computer interface software. Click Here for more detailsReturn to top