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 nebulizatio n in inductively coupled plasma mass spectrometry, with mixed-gas plasmas a nd flow injection, in an attempt to facilitate the quantitative analysis of heterogeneous materials such as soils. Matrices analyzed ranged from marin e sediment to metal-contaminated soil, and were chosen for their variety in elemental composition and matrix structure. Slurries were prepared by firs t grinding the material to less than 3 mu m in high-purity water and then d iluting to 0.1% (w/v) with 1 mol dm(-3) HNO3, which served as both a disper sing and a leaching agent. The resulting slurries were injected (0.25 cm(3) ) into a deionized distilled water carrier. Under these conditions, the sen sitivity was about 85% of that achieved by continuous nebulization. Multiva riate optimization of the nitrogen percentage, forward torch power, and aer osol carrier gas flow rate was conducted to find conditions maintaining sen sitivity constant between different slurries. Since no set of conditions wa s optimal for all elements, a compromise set was selected, which resulted i n accurate results for La and Pb in a series of reference materials, by cal ibrating with aqueous standards. On the other hand, the results for V and C r were almost systematically low, indicating that the compromise plasma con ditions did not allow complete atomization/ionization of these elements.