Reliable determination of SiO2 concentrations in sediments via sequential leaching and ICP-OES/MS analysis

Abstract

Although one of the most abundant elements in bulk Earth, silicon has not received enough attention during routine elemental analysis by ICP-OES and ICP-MS as the standard methods cannot readily obtain Si due to its volatile SiF4 removal during standard HF-HNO3 digestion. This study developed a detailed calculation method for SiO2 concentrations in a sequential analysis of sediment samples based on the mass balance principle. The prerequisite of our calculation is that (in)organic carbon is effectively removed through acid leaching and high-temperature ignition. In this study, powdered geologic reference materials were treated with a two-step sequential leaching method of i) 1 mol/L HCl to digest authigenic minerals such as carbonates followed by ii) ignition in a muffle furnace to remove remaining organic matter and a concentrated HF-HNO3 high pressure-temperature digestion to attack the detrital silicate residues. Five reference materials, GSR4, GSR5, GSR6, GSD9, and GSD10, were selected to verify the trueness of our procedure. The SiO2 contents of geostandards showed good agreement with reference values. The precisions of calculated SiO2 values are better than 0.46 %; 1σ, n ≥ 3, and the accuracies are better than 2 %; 1 RSD, n ≥ 3, compared to the reference values. For other elements, the accuracy and precision of calculated results in bulk samples (i.e., the sum of leached and residual phases) are generally better than 15 %; 1 RSD, n ≥ 3, except for a few elements with extremely low concentrations. This strategy has the advantages of low sample consumption, high efficiency, and helps saving time and labour costs compared to separate sample preparation and analysis for SiO2 and the other major/trace elements.