SEQUENTIAL SPECIATION OF SELENIUM BY FLOW-INJECTION CATHODIC STRIPPING VOLTAMMETRY

A semi-automatic continuous method for the determination of Se(IV) based on flow-injection cathodic stripping voltammetry (FICSV) is reported. The flow injection approach incorporates a thin mercury film on glassy carbon as the working electrode, on which Se(IV) is deposited at an applied potential of 0.0 V. A cathodic scan (from 0.0 to - 0.9 V) is applied and the Se is stripped at - 0.54 V, providing a current intensity proportional to the Se(IV) concentration in the sample. This method features a linear determination range between 0.5 and 30 ng/ml (r(2) = 0.998, RSD = 3.6%). The non-interference levels (foreign species to analyte ratio) are 2.5 : 1 for Cu(II), 7.5:1 for Pb(II), 35:1 for Cd(II), 250:1 for Zn(II) and 500:1 for Fe(III). After developing the method for Se(IV), the speciation of this element has been performed by sequential injection of the dissolved sample into a carrier which may or may not have been previously reduced off-line thus determining the sum (Se(IV) + Se(VI)) or only Se(IV), respectively. The method has been applied to selenium speciation in water samples.