A method for stable carbon isotope ratio and concentration measurements of ambient aromatic hydrocarbons

Abstract

Abstract.A technique for compound-specific analysis of stable carbon isotope ratios and concentration of ambient volatile organic compounds (VOCs) is presented. It is based on selective VOC sampling onto adsorbent-filled cartridges by passing large volumes of air (up to 80 L) through the cartridge. The hydrocarbons are recovered by thermal desorption followed by two-step cryogenic trapping and then are separated by gas chromatography in the laboratory. Once separated, individual VOCs are subjected to online oxidation in a combustion interface and isotope ratio analysis by isotope ratio mass spectrometry. The method allows measurements of stable carbon isotope ratios of ambient aromatic VOCs present in low pptV to ppbV levels with an accuracy of typically better than 0.5 ‰. The precision of concentration measurements is better than 10 %. Examples of measurements conducted as part of a joint Environment Canada-York University (EC-YU) measurement campaign at a semi-rural location demonstrate that the ability to make accurate measurements in air with low VOC mixing ratios is important to avoid bias from an overrepresentation of samples that are strongly impacted by recent emissions.

Atomic spectrometry update – a review of advances in environmental analysis

“…A technique for compound specic analysis of stable carbon isotope ratios of ambient VOCs was developed. 89 It was based upon the selective sampling of VOCs onto sorbent cartridges which are recovered and separated by a TD-GC-MS followed by on-line oxidation in a combustion interface prior to IRMS. The method allowed measurements of isotope ratios of VOCs present in ambient air at low pptv to ppbv concentrations with an accuracy of typically better than 0.5&.…”