Development of a stable isotope approach for the inductively coupled plasma-mass spectrometry determination of oxidized metallothionein in biologicalmaterials

The use of isotope dilution analysis (IDA) with inductively coupled plasma- mass spectrometry (ICP-MS) for the determination of oxidized metallothionei n (MT) by a Cd-saturation method is investigated. The method developed here is a modification of an earlier methodology which used a radioactive Cd is otope (Cd-109). While retaining the many advantages of this previous approa ch, the procedure presented here uses stable isotope ratio measurements (Cd -114/Cd-111) for th, determination of NIT. Experimental parameters governin g the instrumental precision and accuracy for isotope ratio measurements of Cd by ICP-MS were characterized. Systematic errors, including mass bias, d etector dead time, and spectroscopic interferences, could be easily correct ed. The isotope dilution ICP-MS method was validated by the determination o f very low levels of cadmium in biological certified reference materials (N IST SRM 2610 freeze-dried urine, IAEA H-8 horse kidney, and BCR TP-25 liche ns). Finally, the IDA procedure was evaluated for the determination of oxid ized MT by a Cd-saturation method previously developed using radioactive Cd -109. The final procedure was applied to the quantification of MT in Long-E vans Cinnamon rat liver cytosol samples and the results were compared with data obtained for the same samples using the reference Cd-109 methodology. A good agreement between the analytical values obtained by both methods was observed. (C) 2000 Academic Press.