Application of the interference standard method for the determination of sulfur, manganese and iron in foods by inductively coupled plasma mass spectrometry

The interference standard method (IFS) is evaluated to improve the accuracy of the determination of S, Mn and Fe in meat and grain samples by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). Due to ICP-QMS relatively low resolution, polyatomic interferences caused by O-16(2)+. ((OH)-O-16)(2)(+), (ArNH+)-Ar-40-N-14, and (ArO+)-Ar-40-O-16, for example, can compromise determinations at m/z 32, 34, 55, and 56, respectively. In IFS, differently from traditional internal standard methods, plasma naturally occurring species are used to correct for variations in the interference signal rather than the analyte signal. The method is based on the hypothesis that the interfering ion and the IFS probe present similar behaviors in the plasma, and that by using the analytical (analyte plus interference)/IFS signal ratio one could reduce variations due to interference and, consequently, improve accuracy. In this work, this strategy is evaluated in real sample applications and significant improvements on accuracy are observed for S-32, S-34, Mn-55, and Fe-56 determinations. Recoveries ranging from 72% for Mn to 105% for Fe in two different standard reference materials are obtained using the Ar-38 probe. These analytes are successfully determined in meat and grain samples with concentrations ranging from 4.42 mu g g(-1) for Mn in corn to 7270 mu g g(-1) for Sin chicken liver. The method is compared with other strategies such as internal standardization and mathematical correction. No instrumental modification or introduction of foreign gases is required, which is especially attractive for routine applications. (C) 2011 Elsevier B.V. All rights reserved.