C-13 C-12 RATIO MEASUREMENTS OF AROMATIC-MOLECULES USING PHOTOIONIZATION WITH TOF MASS-SPECTROMETRY/

We demonstrate a method for measuring the carbon isotope ratios of aro matic molecules without the need for chemical preparation. The techniq ue employs a time-of-flight (TOF) mass spectrometer equipped with a du al microchannel plate detector assembly. We present the measurement of carbon isotope ratios for m-xylene-d(10) (C6D4(CD3)(2)), toluene (C6H 5CH3), and toluene-d(8) (C6D5CD3). Gas-phase samples are photoionized with the 266 nm output of a Nd:YAG laser, and the abundance of C-12 an d C-13 in the molecules is derived from the TOF spectra. Complications caused by and corrections for detector nonlinearity and parent ion fr agmentation are discussed.