Comparison of three different instrumental approaches to the determination of iron and zinc isotope ratios in clinical samples

Stable isotopes can be used to investigate the absorption of nutritionally important elements in humans. Although thermal ionisation mass spectrometry (TIMS) is the benchmark technique for accuracy and precision in isotope ratio measurement, the lengthy sample preparation procedures and analysis times required can present significant disadvantages. Inductively coupled plasma mass spectrometry (ICP-MS) is now a well-established technique for isotopic determinations and can be used following only a simple sample preparation (microwave-assisted digestion followed by a dilution step). The advantage of this is that it can provide comparable data to that from TIMS, but in a significantly shorter analysis time. This study assesses the accuracy and precision of two ICP-MS instruments for the determination of Fe and Zn isotope ratios in faecal samples by comparison with TIMS data. Using standard statistical techniques, no significant differences were found between data obtained from TIMS, double-focussing ICP-MS or a single-focussing ICP-MS equipped with a collision cell.