Partial leaching as an aid to slurry nebulization for the analysis of soils by ICP-MS with flow injection and mixed-gas plasmas

Acid leaching (with 1 mol dm-3 HNO3) was combined with slurry nebulization in inductively coupled plasma mass spectrometry, with mixed-gas plasmas and flow injection, in an attempt to facilitate the quantitative analysis of heterogeneous materials such as soils. Matrices analyzed ranged from marine sediment to metal-contaminated soil, and were chosen for their variety in elemental composition and matrix structure. Slurries were prepared by first grinding the material to less than 3 μm in high-purity water and then diluting to 0.1% (w/v) with 1 mol dm-3 HNO3, which served as both a dispersing and a leaching agent. The resulting slurries were injected (0.25 cm3) into a deionized distilled water carrier. Under these conditions, the sensitivity was about 85% of that achieved by continuous nebulization. Multivariate optimization of the nitrogen percentage, forward torch power, and aerosol carrier gas flow rate was conducted to find conditions maintaining sensitivity constant between different slurries. Since no set of conditions was optimal for all elements, a compromise set was selected, which resulted in accurate results for La and Pb in a series of reference materials, by calibrating with aqueous standards. On the other hand, the results for V and Cr were almost systematically low, indicating that the compromise plasma conditions did not allow complete atomization/ionization of these elements.Key words: inductively coupled plasma mass spectrometry, slurry nebulization, flow injection, mixed-gas plasma.