Determination of silicon in soil extracts by flow injection analysis

Abstract

A flow injection analysis (FIA) procedure is described by which dissolved silicon can be determined in complex aqueous media such as soil extracts at a rate of 35 determinations per hour. The determination is based on molybdenum blue, which is formed by reduction of β-molybdosilicate by ascorbic acid. In order to accelerate the formation of β-molybdosilicate and the decomposition of molybdophosphate, formed in phosphate-containing solutions, the determination must be carried out at a temperature near 80 °C. The analytical precision (coefficient of variation) is about 2% and the limit of detection (k= 3) is about 30 ng ml^–1 of SiO₂. Dithionite, EDTA, Al, Fe and P, in concentrations above those in soil extracts diluted to contain less than 1.0 µg ml^–1 of SiO₂, do not interfere, if dithionite is oxidised by aeration prior to the determination of silicon.

The silicon contents in various soil extracts determined by the proposed FIA procedure were in good agreement with those determined by a well established manual photometric procedure.