Application of HR-ICP-MS for the simultaneous measurement of zinc isotope ratios and total zinc content in human samples

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Abstract
Zinc is an essential element to humans, and accurate measurements of zinc isotope ratios and total zinc content in metabolic studies are therefore crucial. In the present study a new method is described for the simultaneous measurement of zinc isotope ratios (64Zn+/66Zn+, 67Zn+/66Zn+, 68Zn+/66Zn+ and 70Zn+/66Zn+) and total zinc content in human faeces, urine and serum using high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). Relative standard deviations (RSD) of 0.7% were found for 67Zn+/66Zn+, 68Zn+/66Zn+ and 70Zn+/66Zn+, while a RSD of 1.2% was found for 64Zn+/66Zn+. Judged by the analysis of faecal sample solutions spiked with enriched 68Zn the accuracy of the isotope ratio measurements is high. The measurement of total zinc content showed a fairly good agreement with atomic absorption spectrometry (AAS) data. Using a mass resolution of 6000 all zinc isotopes could be measured free from interferences, except for 64Zn+, where the overlap from 64Ni+ had to be corrected for mathematically. The use of different mass resolution settings ensured a positive identification of all spectral interferences found on the zinc isotopes in faeces, urine and serum.