QUADRUPOLE ICP - MASS-SPECTROMETRY FOR THE DETERMINATION OF THE AQUA REGIA SOLUBLE CONTENT OF TRACE-METALS IN SOIL AND SLUDGE CANDIDATE REFERENCE MATERIALS

In the framework of a certification campaign, organised by the Europea n Community Bureau of References (BCR), quadrupole inductively coupled plasma - mass spectrometry (ICP-MS) was used for the determination of the aqua regia soluble contents of Mn, Co, Ni, Cu, Zn, Cd, Hg and Pb in three different soil and sludge candidate reference materials (BCR CRM 141R, 144R and 146R). Especially for the transition metals, for wh ich accurate quantitation is often hampered by the presence of spectra l interferences, great care was taken in avoiding systematic errors du e to overlap with signals from polyatomic ions and/or isobaric nuclide s showing the same nominal mass as the nuclides of interest. Si-based interferences were avoided by additional HF-treatment of the samples o btained after aqua regia extraction. The presence of other potential i nterferences was checked by registration of signal behaviour plots (si gnal intensity as a function of the nebulizer gas flow rate) and/or me asurement with a high resolution ICP - mass spectrometer. In order to obtain the highest accuracy possible, bath external standardization an d the method of standard additions were used for calibration and the r esults obtained were compared. Hence it was shown that, despite the us e of an internal standard, for some elements accurate results could on ly be obtained using the method of standard additions. Finally, for Hg and Pb, besides the calibration techniques already mentioned, also is otope dilution was used. For all materials analysed, the results obtai ned are in excellent agreement with the values finally certified.