Routine analysis by high precision gas chromatography mass selective detector isotope ratio mass spectrometry to 0.1 parts per mil

Stable isotope methods are potentially quite useful for validating natural or enhanced mineral degradation of contaminants, For this reason, a continu ous flow gas chromatograph (GC), isotope ratio mass spectrometer (IRMS) has been coupled with a quadrupole mass selective detector (MSD) to allow simu ltaneous mass spectral and stable carbon isotope ratio data to be obtained from a single chromatographic analysis. This allows the target contaminant and any extra-cellular degradation intermediates to be both qualified and q uantified. Previously acceptable limits of precision (0.3 parts per mil) ar e undesirable given the small fractionation observed during aerobic degrada tion. To further understand the fate of organic contaminants and to gain in formation about the metabolic degradative pathway employed by a microorgani sm, routine isotopic analyses on a range of analytes have been performed. Q uantities of sample producing mass-44 ion beam signal (I-44) of 2 x 10(-10) fo 1 x 10(-8) A were analysed. When the IRMS was tuned for high sensitivit y, ion source nonlinearities were overcome by peak height correction from a n algorithm that was produced using known isotopic standards of varying con centrations. This led to sample accuracy of <0.01 parts per thousand and sa mple precision of 0.1 parts per thousand. Copyright (C) 1999 John Wiley & S ons, Ltd.