Construction and performance of surfactant-sensitive electrodes

The construction of surfactant-sensitive electrodes presents no difficulty, and three types are described here. The first type is a concentration cell, the second is a conductor coated with a membrane containing a surfactant salt, and the third is a conductor coated with a membrane not containing a surfactant salt. Many other electrodes have been described in the literature over the last 20 years or so, but most if not all of them are of one of these basic types. 

001 mol/l. The inclusion of the surfactant is said to improve selectivity, but the evidence for this is unconvincing. 

Such an electrode can be made as follows. Capped silver-silver chloride electrodes may be obtained from most laboratory suppliers. 

Accurately weigh 0.1063 g pure dry sodium dodecyl sulphate and 0.1719 g pure dry benzethonium chloride monohydrate, dissolve in tetrahydrofuran (caution flammable toxic vapour) and dilute to 

100 ml in a volumetric flask. Centrifuge to remove the precipitated sodium chloride. This yields a solution containing 0.25% benzetho-nium dodecyl sulphate (BDS). 

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