SAMPLE PREPARATION FOR INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRIC DETERMINATION OF THE ZINC-70 TO ZN-68 ISOTOPE RATIO IN BIOLOGICAL SAMPLES

Sample preparation was optimized for the Zn-70:Zn-68 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 Zn-70. 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 Cl-35(2)+, and the procedure was modified to evaporate the CCl4. Extraction was unnecessary for faecal samples. Under optimized conditions the Zn-70:Zn-68 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).