Minimization of sample requirement for δ 18 O in benzoic acid

The measurement of the oxygen stable isotope content in organic compounds has applications in many fields, ranging from paleoclimate reconstruction to forensics. Conventional High‐Temperature Conversion (HTC) techniques require >20 µg of O for a single δ 18 O measurement. Here we describe a system that converts the CO produced by HTC into CO 2 via reduction within a Ni‐furnace. This CO 2 is then concentrated cryogenically, and 'focused' into the isotope ratio mass spectrometry (IRMS) source using a low‐flow He carrier gas (6–8 mL/min). We report analyses of benzoic acid (C 7 H 6 O 2 ) reference materials that yielded precise δ 18 O measurement down to 1.3 µg of O, suggesting that our system could be used to decrease sample requirement for δ 18 O by more than an order of magnitude. Copyright © 2010 John Wiley & Sons, Ltd.