Online wet oxidation/isotope ratio mass spectrometry method for determination of stable carbon isotope ratios of water-soluble organic carbon in particulate matter.

Abstract

Water-soluble organic carbon (WSOC) is formed by oxidation of organic compounds in particulate matter (PM) and accounts for 25-80% of the organic carbon in PM. Stable carbon isotope ratio (δ13 C) analysis is widely used to identify the sources of PM, but determining the δ13 C values of WSOC is complicated and requires a time-consuming pretreatment process. We have developed an online wet oxidation/isotope ratio mass spectrometry method with a reduced pretreatment time. We have measured the δ13 C values of WSOC by using this method. The method showed high accuracy (0.1‰) and precision (0.1‰) for levoglucosan, and the limit of detection was sufficiently low for WSOC analysis. Using this method, we determined δ13 C values of WSOC in PM2.5 samples collected in Japan during the period from July to November 2017 and found that the values ranged from -26.5‰ to -25.0‰ (average, -25.8‰). Our simple, low-blank method could be used for rapid quantitative analysis of the δ13 C values of WSOC in PM2.5 . We propose that this online method be used as a standard method for δ13 C analysis of WSOC.