Quantification of heavy metals in clays by dry plasma laser ablation-ICP-MS

Abstract

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is applied for the analysis of powdered clays used for water filtration. For the quantitative determination of trace element concentrations in clays, three matrix dilutions of red clay (RAIP) and brick clay-679 (NBS) reference materials are used to perform calibration curve. A mixture of ultrapure graphite and powders of the samples and reference materials are homogenized by using a shaker. It is found that the ablation efficiency is better in case of raster mode than single point mode in laser ablation. Calibration curves for trace elements were measured without and with 13C as internal standard element. 13C is used to compensate for signal fluctuations caused by the variation of the ablated sample mass. The regression coefficients of the calibration curves are better than 0.98 with internal standardization. This quantification method provided analytical results with deviations of 5–12% from the recommended and proposed values in clay-679 (NBS). In order to compare two different approaches for the quantification of analytical results in LA-ICP-MS, relative sensitivity coefficients (RSCs) of trace elements is determined using 88Sr as internal standard in red clay (RAIP). The experimentally obtained RSCs are in the range of 0.3–4.9 for all elements of interest. Therefore, the measured concentrations are corrected with RSCs. The relative standard deviation (R.S.D.) of the determination of the trace element concentration is about 3–9%. Heavy metal concentrations obtained by the two quantification methods in LA-ICP-MS are compared with the concentrations obtained by graphite furnace-atomic absorption spectrometry (GF-AAS).