A novel method for compound specific determination of delta C-13 in volatile organic compounds at ppt levels in ambient air

A novel method for the compound specific determination of delta(13)C in VOC is presented. It combines a cryogenic preconcentration procedure with gas chromatograph,ic separation, on-line combustion and isotope ratio mass spectrometry. The method allows the determination of delta(13)C values of VOC at sub ppb levels with a precision of 0.5 parts per thousand. The procedure is suitable for routine operation. The accuracy of the method is of the same quality as the reproducibility of the measurements. The first ever measurements of delta(13)C in selected VOC in clean air are presented and compared with data from samples of contaminated air. The variability in the delta(13)C values of atmospheric VOC is much larger than the accuracy and precision of the measuring method. Hence the technique will be a very valuable tool to complement concentration measurements of VOC and to improve our understanding of the processes governing the distribution of VOC in the atmosphere.