13C/12C ratio measurements of aromatic molecules using photoionization with TOF mass spectrometry

We demonstrate a method for measuring the carbon isotope ratios of aromatic molecules without the need for chemical preparation. The technique employs a time-of-flight (TOF) mass spectrometer equipped with a dual microchannel plate detector assembly. We present the measurement of carbon isotope ratios for m-xylene-d10 (C6D4(CD3)2), toluene (C6H5CH3), and toluene-d8 (C6D5CD3). Gas-phase samples are photoionized with the 266 nm output of a Nd:YAG laser, and the abundance of 12C and 13C in the molecules is derived from the TOF spectra. Complications caused by and corrections for detector nonlinearity and parent ion fragmentation are discussed.