18O/16O ratio measurements of inorganic and organic materials by elemental analysis-pyrolysis-isotope ratio mass spectrometry continuous-flow techniques.

We have used a high-precision, easy, low-cost and rapid method of oxygen isotope analysis applied to various O-bearing matrices, organic and inorganic (sulfates, nitrates and phosphates), whose (18)O/(16)O ratios had already been measured. It was first successfully applied to (18)O analyses of natural and synthetic phosphate samples. The technique uses high-temperature elemental analysis-pyrolysis (EA-pyrolysis) interfaced in continuous-flow mode to an isotope ratio mass spectrometry (IRMS) system. Using the same pyrolysis method we have been able to generate a single calibration curve for all those samples showing pyrolysis efficiencies independent of the type of matrix pyrolysed. We have also investigated this matrix-dependent pyrolysis issue using a newly developed pyrolysis technique involving 'purge-and-trap' chromatography. As previously stated, silver phosphate being a very stable material, weakly hygroscopic and easily synthesized with predictable (18)O/(16)O values, could be considered as a good candidate to become a reference material for the determination of (18)O/(16)O ratios by EA-pyrolysis-IRMS.