Adsorption–concentration of ion associate formed between molybdosilicate and Malachite Green on a miniature filter: its application to trace and ultratrace determination of silicon

Abstract

Adsorption phenomenon of the ion associate of molybdosilicate was examined by a small-scale procedure and applied to the concentration of trace and ultratrace amounts of silicon. A sensitive and reproducible spectrophotometric method for the determination of trace and ultratrace amounts of silicon was developed by measuring absorbances using a flow injection technique. The coloured ion associate formed between molybdosilicate and Malachite Green (MG) was filtered through a miniature membrane filter (cellulose nitrate; pore size, 1.0 µm; 9 mm diameter), dissolved together with the membrane filter in 1 cm³ or less of methyl Cellosolve; the absorbance of the solution was then measured at 627 nm with a flow-through system equipped with an autosampler. The absorbance, the standard deviation and the relative standard deviation of the reagent blank were 0.0230, 0.0010 and 4.4%, respectively, when 30 cm³ of sample solutions were used; the detection limits were 14 and 7 ppt of silicon, respectively, when 30 and 60 cm³ of sample solutions were used, respectively. The calibration graph was linear up to 9 ng cm^–3(9 ppb) of silicon using 15 cm³ of sample solution. By using the proposed method, silicate ion concentrations in highly purified water samples were determined.