Comparison of two methods for the determination of water-soluble organic carbon in atmospheric particles

In this work, we have compared two methods for the determination of water-soluble organic carbon (WSOC) in ambient aerosols, one based on a total organic carbon analyzer (TOC) and the other based on an aerosol carbon analyzer (ACA). The two instruments entail different pre-analysis treatment of aerosol water extracts. Standard compounds spiked onto filters showed satisfactory recovery ranging from 75% to 105% by the two methods, demonstrating that the extraction procedures and subsequent pre-analysis pre-treatment are quantitative in both methods. Measurements of standard compounds and aerosol samples show that the two methods give equivalent results by paired t-test. The TOC method offers a limit of detection (LOD) of 2.6 μg/sample, whereas the ACA method gives a LOD of 4.8 μg/sample. Acid treatment to remove carbonate carbon was found unnecessary for the determination of WSOC in PM2.5 aerosols. Although the sample treatment procedures and the detection limits of these two methods are different to some extent, both are suitable for the determination of WSOC in aerosol samples. The TOC method has the advantages of requiring less time in sample pre-treatment and offering slightly lower detection limit. The TOC instruments also have the additional advantage of automated sample analysis while the ACA instruments require manual operation.