LAUSR

To prepare thiocyanate-selective chemical sensors, a sol–gel-based matrix was employed as a host membrane for the encapsulation of a sensing material. Tricaprylylmethylammonium thiocyanate (Aliquat336-SCN) was used as the dissociated ion-exchanger type sensing ionophore. Both 3isocyanatopropyl-triethoxysilane and 1,4-butanediol were used for appropriate precursor preparation. Under acidic conditions, the sol precursor slowly gelled to yield a film in which the thiocyanate ionophore, Aliquat336-SCN, was encapsulated. Electrochemical responses of the potentiometric sensors were compared to those of traditional poly(vinyl chloride) (PVC) membrane electrodes prepared using the same ionophore. On the 7 th working day, the average response slope toward thiocyanate was approximately 56.3 mV decade -1 in the concentration range 10 -4.5 M to 5 × 10 -1 M at 20°C. Selectivity toward thiocyanate over lipophilic anions such as perchlorate and salicylate was considerably improved. The results exhibit a clear tendency that deviates from the Hofmeister selectivity pattern which would be observed in a membrane electrode made of Aliquat336-SCN type salt. The potentiometric selectivity coefficients, as measured in a 0.05 M 2-morpholinoethanesulfonic acid monohydrate buffer, pH 5.5, were log k pot thiocyanate, chloride = − 2.3, log k pot thiocyanate, salicylate = − 0.6, and log k pot thiocyanate, perchlorate = − 0.1. The optimized membrane sensors were employed for the flowinjection measurement of thiocyanate levels in saliva samples from both smokers and nonsmokers. The membrane sensors exhibited a fairly good correlation with the traditional colorimetric method (n = 23; sensors = 0.84 (colorimetric) + 0.13: R 2 = 0.97).