THERMAL LENS DETERMINATION OF VANADIUM(V) AND ITS ACTIVATORS BY OXIDATION OF ANILINE BY BROMATE IONS

A dual-beam thermal lens spectrometer was used to study the possibilit ies of utilizing thermal lens spectrometry in kinetic methods as exemp lified by the well known oxidation of aniline by bromate ions catalyse d by vanadium(v) in the presence of 8-hydroxyquinoline or pyrocatechol as catalyst activators, This approach allowed a 100-fold decrease in the limits of detection of vanadium (3 x 10(-10) mol l(-1)) and a 10-f old decrease in the limits of detection of both activators (1 X 10(-5) mol l(-1) for 8-hydroxyquinoline and 2 x 10(-5) mol l(-1) for pyrocat echol). It was found that the thermal lens kinetic curve, after an ind uction period, becomes nearly exponential and rapidly grows to the max imum thermal lens signal, This phenomenon can be accounted for by the accelerated formation of a colloidal solution of the reaction products , which are poorly soluble in water, in the volume irradiated by the l aser beam, The parameters of the exponential curve depend on the conce ntrations of the reductant and the activator, The sensitivity of the d etermination of 8-hydroxyquinoline and pyrocatechol by the use of the exponential curve is 5 x 10(-6) and 1 x 10(-5) mol l(-1), respectively , New parameters of the curve can be used to develop procedures for th e simultaneous determination of the participants of the reaction.