Enhanced semiquantitative multi-analysis of trace elements in environmental samples using inductively coupled plasma mass spectrometry

Abstract

A semiquantitative procedure for the determination of trace metals in natural waters and sediments by ICP-MS was developed. The method is based on the establishment of the instrumental molar response curveversus mass using a multi-elemental solution containing elements from Mg to Bi with different ionisation potentials. The ionisation conditions in the plasma (electron density, n_e, and ionisation temperature, T_ion) were determined by least-squares fitting, using the Saha equation, by adjusting the molar response curve to a third-order polynomial. The effect of matrix constituents, such as Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^– and SO₄^2–, on both the shape of the molar response curve and on the plasma ionisation conditions was evaluated. It was observed that the ionisation degrees calculated in the plasma did not change significantly in the presence of the matrix constituents. However, the shape of the molar response curve was affected by high concentrations of matrix components and this effect was corrected by adding internal standards to the samples. The semiquantitative procedure was applied to the analysis of local natural waters and the results were compared with those obtained by external calibration and standard additions. Validation was performed by analysis of riverine water (SLRS-3) and sediment (PACS-1 and MESS-2) reference materials from the National Research Council of Canada with satisfactory results.