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

Double-focusing sector field inductively coupled plasma mass spectrometry ( ICP-MS) was used for the determination of Mg-26/Mg-24 isotope ratios in ord er to quantify intestinal Mg2+ transport in the fish tilapia (Oreochromis m ossambicus). As the sample medium contained substantial amounts of C, Na, P , S, Cl and K, the occurrence of molecular (e.g., C-2(+), C2H+, CN+ and NaH +) and doubly charged (Ca-48(2+)) ions acid tailing of the Na-23(+) ion sig nal resulted in spectral overlap at low mass resolution. Application of a h igher mass resolution (R = 3000), however, permitted accurate determination of ME isotope ratios. The usefulness of cool plasma conditions was also ev aluated, but this approach was insufficient to resolve all interferences co mpletely. After careful optimisation of the measurement parameters, it was possible to measure the Mg-26/Mg-24 isotope ratio with a relative standard deviation (RSD) of 0.2-0.5% (n = 10 x 30 s) at R = 3000. From the isotope r atio results obtained, net intestinal Mg2+ fluxes were calculated, providin g evidence for secretory Mg2+ transport. Conclusively, the measurement of s table isotope ratios with sector field ICP-MS presents a sophisticated tool for the study of Mg2+ transport processes in biological systems that may p rovide an effective alternative for the use of radiotracers.