Sensitive stripping voltammetry of silicon(IV) and its application to steel analysis

The commonly used methods for the determination of trace silicon exhibit po or sensitivity, although there is a strong need to develop a sensitive and simple method. A highly sensitive differential pulse adsorptive stripping v oltammetry based on the electrochemical characteristics of beta -silicodode camolybdate was devised for silicon determination. A complex of silicon(IV) with hexaammonium heptamolybdate, beta -silicododecamolybdate, was adsorbe d on a glassy carbon electrode at -1.1 V vs. Ag/AgCl for 10 min in a hydroc hloric-nitric acids mixture solution containing acetone, and was ultimately reduced to molybdenum (IV) oxide. The deposits were then stripped by a pos itive-going scan to -0.2 V vs. Ag/AgCl at a rate of 50 mV s(-1). A single w ell-defined peak was observed at around -0.7 V vs. Ag/AgCl in the stripping curves. The unreacted heptamolybdate was masked with sodium tartrate, whic h acted as a masking agent of matrix iron (III). The calibration curve (pea k area vs. concentration) was linear over the 0.5 to 100 ngSi(rV) cm(-3) (1 .8 x 10(-8) similar to 3.6 x 10(-6) mol dm(-3)) concentration ranges, with a sensitivity of 0.21 muA-V(ng cm(-3))(-1). The detection limit (3 sigma) w as 4.3 x 10(-9) mol dm(-3). The proposed method was applied to the direct d etermination of 0.87 massppm of silicon in high-purity iron with an RSD of ca. 6%; its lower limit of determination was two orders of magnitude better than that of the current JIS method for chemical analysis. The time requir ed for the whole procedure was within 80 min. No interference resulted from the foreign elements, which could form heteropoly acids with heptamolybdat e.