Factors affecting the limit of detection of sodium-responsive glass electrodes

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Abstract
Factors affecting the limit of detection of sodium-responsive glass electrodes have been examined and it is postulated that the ultimate limit is set by the dissolution of alkali metal ions from the glass membrane itself. Experimental results are presented that are consistent with this hypothesis and from which the following conclusions can be drawn: (a) measurements of very low sodium concentrations are favoured by high linear flow-rates of solution past the membrane surface and by having as low a sample temperature as possible, consistent with acceptable response times; (b) hydrogen-ion interference is negligible provided that the pH is greater than 10.5; (c) interference of ions from the alkaline additive is similarly negligible if an alkylamine such as diethylamine is used. The limit of detection obtained with EIL GEA.33 electrodes in an EIL flow cell with a flow-rate of 4 ml min–1 was about 0.07 µg l–1 of sodium at 20 °C, when the pH was adjusted to 11.0 with diethylamine.

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