Heavy metal trace determination with a compact thermal ionization quadrupole mass spectrometer

Summary

The analytical procedure for the trace determination of Pb, Cd, Cu, and Zn in sewage sludges, soils, and analogous materials by isotope dilution mass spectrometry with a compact thermal ionization quadrupole instrument, which was described in the first part of this publication, is transferred to food samples in this paper. Heavy metal concentrations in different ranges of content are analysed in meat, liver, kidney, wholemeal flour, and bread samples. In addition, iron is determined in the first three samples mentioned besides the other heavy metals by a new technique developed with thermal ionization mass spectrometry. In all cases Pb, Cd, and Cu are isolated in one step by electro-deposition after decomposition of the sample. Afterwards, these three elements are successively measured in a thermal ionization quadrupole mass spectrometer. Zn and Fe are separated chromatographically using a column filled with an anion-exchanger resin. The mass spectrometric measurement of zinc and iron is carried out separately isolating these elements from the same decomposed sample. The heavy metal concentrations determined by isotope dilution mass spectrometry agree well with results of other analytical methods, which were obtained during a certification campaign for food samples. The detection limits of isotope dilution mass spectrometry are 1.2 ng/g for Pb, 0.8 ng/g for Cd, 9 ng/g for Cu, 27 ng/g for Zn, and 12 ng/g for Fe. These detection limits enable the analysis of the corresponding heavy metals in all important food samples. The use of the described compact and easy to handle thermal ionization quadrupole mass spectrometer opens the possibility to apply the described isotope dilution technique not only as a calibration method but also as a routine method in food analyses.