Sample preparation for inductively coupled plasma mass spectrometric determination of the zinc-70 to zinc-68 isotope ratio in biological samples

Abstract

Sample preparation was optimized for the 70Zn:68Zn isotope ratio determinations performed with inductively coupled plasma mass spectrometry in blood, faces and urine from human pre-term babies after oral or intravenous administration of enriched 70Zn. The preparation techniques achieved complete decomposition, matrix separation, maximum preconcentration and minimum contamination. After sample decomposition, Zn was extracted into CCl4 with ammonium pyrrolidin-1-yldithioformate and back extracted into 1.2 mol dm–3 HNO3 for analysis. Residual chloride resulting from dissolved CCl4 in the acid led to interference by 35Cl2+, and the procedure was modified to evaporate the CCl4. Extraction was unnecessary for faecal samples. Under optimized conditions the 70Zn:68Zn isotope ratio can be measured with acceptable precision ( 200 ng cm–3 in the analytical solution).