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

Sample preparation was optimized for the ⁷⁰Zn:⁶⁶Zn isotope ratio determinations performed with inductively coupled plasma mass spectrometry in blood, faeces 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 (<1% relative standard deviation) for samples with sufficient levels of Zn (>200 ng cm^-3 in the analytical solution).