ACCURACY IN SPECIES ANALYSIS - SPECIATED ISOTOPE-DILUTION MASS-SPECTROMETRY (SIDMS) EXEMPLIFIED BY THE EVALUATION OF CHROMIUM SPECIES

Speciated isotope dilution mass spectrometry (SIDMS) improves accuracy in the determination of chemical species in samples. It can be used t o measure elements in their oxidation states as well as in organometal lics or other molecular forms of species. SIDMS compensates for specie s transformations that occur in many of the steps of sample processing , including sampling process, storage, sample preparation and speciate d measurement. It is also a diagnostic tool for identifying the most e rror prone steps. These combined capabilities provide a new method for establishing standard, legally defensible measurement tool in speciat ion analysis. Early speciation studies of Cr(VI) and Cr(III) demonstra te the unique advantages of SIDMS. Thus far, SIDMS has corrected up to 80% of the reduction of Cr(VI) to Cr(III). In theory, using SIDMS mak es it possible to correct up to 90% species conversion with good preci sion. This paper describes how to apply the method to chromium and pro vides examples of the general steps. (C) 1998 Elsevier Science B.V.