Analysis of oxygen-18 in orthophosphate by electrospray ionisation mass spectrometry

Isotope distributions in phosphate are useful measurements in geochemical systems since they give information on origin and environmental oxygen exchange processes. It is often necessary to perform measurements rapidly at the parts per million level on milligram quantities of sample. However, current methodologies require conversion to gas and/or time consuming multiple precipitation steps or insensitive nuclear magnetic resonance (NMR) techniques. in the electrospray method developed here, lengthy analyses requiring precipitation of phosphate are unnecessary. Moreover, there is no requirement for conversion to a simple gas and indirect evaluation. Accuracy is demonstrated by good agreement with NMR measurements on concentrated laboratory prepared chemical solutions. After dilution, electrospray analyses gave similar results. (C) 2000 Elsevier Science B.V.