The screen-printed sensor as a detector in surfactant determination

Synthetic surface-active substances (surfactants) are produced worldwide in large amounts. Surfactants as environmental pollutants are present in various materials, including natural and waste waters, process solutions of industrial enterprises, household consumer products, etc. The most widely used technique in ionic surfactant analysis is the so-called two-phase titration method, but this technique suffers from a large number of drawbacks (limitation of application to strongly coloured and turbid samples, the toxicity of the organic chlorinated solvent used, the formation of emulsion during titration which can disturb visual end-point detection, the numerous matrix interferences, etc). The potentiometry with ion-selective electrodes (ISE) used as sensors, is a promising, simple, rapid available and inexpensive method for determining surfactants, which overcomes most of the limitations mentioned. The electrode may be sensitive to the analyte or to the titrant. Basically, these electrodes have the same design: the electroactive part of an ISE membrane consists of an ion-pair (C+ A), where A is anion of an anionic surfactant (AS) and C is positively charged counter ion, usually a cation of a cationic surfactant (CS). This kind of ISE is suitable for the detection of A and C+. In this investigations 1, 3-didecyl-2-methylimidazolium-tetraphenylborate (DMI-TPB) was used as sensing ion-pair element which was implemented on a screen-printed carrier, consisting of a conducting substrate as a sensing material carrier and an Ag/AgCl electrode as a reference. Platinum, gold and carbon paste were used as conducting carriers. The sensor was applied for potentiometric determination of single pure and technical grade ionic surfactants and their content in commercial products.