Excimer laser isotope-ratio-monitoring mass spectrometry for in situ oxygen isotope analysis

A technique using isotope-ratio-monitoring gas chromatography-mass spectrometry (irmGCMS) and excimer laser fluorination for in situ oxygen isotope analysis of silicates is described. The irmGCMS and oxygen extraction line is connected by a newly developed interface, reducing the time for a single analysis to less than 10 min. The precision obtained for 5180 is similar to what has been reported for excimer laser fluorination using dual inlet systems. 5180 values of two olivine standards had I sigma precision of +/- 0.14parts per thousand (n 19 and n = 10) and that of Dorentrup, quartz had 0.17parts per thousand. Eleven analyses of a large zircon crystal had a precision of +/- 0.12parts per thousand. However, between 300 and 600 nmol oxygen was liberated for a single analysis, equivalent to cylindrical laser holes 250 to 350 mum in diameter and depth, In the future it will be feasible to measure the isotope ratio of cylindrical volumes 150 pm in diameter simply by reducing the volume of the extraction line. While this is still significantly larger than what is possible with ion probes, the ratios obtained by excimer laser-irmGCMS are highly accurate and precise without correction. The value of this technique for in situ oxygen isotope measurements is demonstrated with two rock slabs from metamorphic rocks of the Dabie-Sulu ultra-high-pressure belt, China. (C) 2002 Elsevier Science B.V. All rights reserved.