Use of double-focusing sector field ICP-mass spectrometry in tracer experiments, aiming at the quantification of Mg2+ transport across the intestine of tilapia fish

Abstract

Double-focusing sector field inductively coupled plasma mass spectrometry (ICP-MS) was used for the determination of 26Mg/24Mg isotope ratios in order to quantify intestinal Mg2+ transport in the fish tilapia (Oreochromis mossambicus). As the sample medium contained substantial amounts of C, Na, P, S, Cl and K, the occurrence of molecular (e.g., C2+, C2H+, CN+ and NaH+) and doubly charged (48Ca2+) ions and tailing of the 23Na+ ion signal resulted in spectral overlap at low mass resolution. Application of a higher mass resolution (R = 3000), however, permitted accurate determination of Mg isotope ratios. The usefulness of cool plasma conditions was also evaluated, but this approach was insufficient to resolve all interferences completely. After careful optimisation of the measurement parameters, it was possible to measure the 26Mg/24Mg isotope ratio with a relative standard deviation (RSD) of 0.2–0.5% (n = 10 × 30 s) at R = 3000. From the isotope ratio results obtained, net intestinal Mg2+ fluxes were calculated, providing evidence for secretory Mg2+ transport. Conclusively, the measurement of stable isotope ratios with sector field ICP-MS presents a sophisticated tool for the study of Mg2+ transport processes in biological systems that may provide an effective alternative for the use of radiotracers.