DETERMINATION OF ZINC STABLE ISOTOPES IN BIOLOGICAL-MATERIALS USING ISOTOPE-DILUTION INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

A method is described for using isotope dilution to determine both the amount of natural zinc and enriched isotopes of zinc in biological sa mples. Isotope dilution inductively coupled plasma mass spectrometry o ffers a way to quantify not only the natural zinc found in a sample bu t also the enriched isotope tracers of zinc. Accurate values for the e nriched isotopes and natural zinc are obtained by adjusting the mass c ount rate data for measurable instrumental biases. Analytical interfer ences from the matrix are avoided by extracting the zinc from the samp le matrix using diethylammonium diethylidithiocarbamate. The extractio n technique separates the zinc from elements which form interfering mo lecular ions at the same nominal masses as the zinc isotopes. Accuracy of the method is verified using standard reference materials. The det ection limit is 0.06-mu-g Zn per sample. Precision of the abundance ra tios range from 0.3-0.8% R.S.D. for natural zinc concentrations of abo ut 200-600-mu-g g-1. The accuracy and precision of the measurements ma ke it possible to follow enriched isotopic tracers of zinc in biologic al samples in metabolic tracer studies.