Examination of sol–gel technique applicability for preparation of pellets for soil analysis by laser ablation inductively coupled plasma optical emission spectrometry

Abstract

Silica sol–gel matter was examined as a binder assisting the preparation of agricultural soil sample pellets for elemental analysis by laser ablation inductively coupled plasma optical emission spectrometry. The sol–gel method, allowing homogenous dispersion of internal standard (Sc) and analytes in calibration pellets, was applied to the determination of Cr, Ni, Cu, Zn and Pb in four types of soils. A Q-switched Nd:YAG laser (1064 nm) was employed for ablation of pellets prepared by pressing of a ground and homogenized blend of soil and silica gel. Calibration curves exhibited correlation coefficients greater than 0.997. The repeatability of determination for elements of interest did not exceed 7% RSD. Accuracy of determination was proved by X-ray fluorescence analysis of soil pellets prepared with a wax binder and by solution analysis after total decomposition of samples by a mixture of HF and HClO₄. The pellet homogeneity was checked by electron probe X-ray microanalysis, measuring element distribution, and the ablation craters were studied using optical microscopy. The depths of the ablation craters exhibited different ablation rates for samples with diverse matrices. Analytical results obtained for CRM by the method presented exhibit bias in the range from 6 to 15% rel. (α = 0.05) depending on the element.