Development of a Compound-Specific Carbon Isotope Analysis Method for Atmospheric Formaldehyde via NaHSO_(3) and Cysteamine Derivatization

摘要

A novel method has been developed for the compound-specific carbon isotope analysis of atmospheric formaldehyde using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). The method allows the determination of the (delta)~(13)C value for atmospheric formaldehyde at nanogram levels with higher precision and lower detection limit. In the present work, atmospheric formaldehyde was collected using NaHSO_(3)-coated Sep-Pak silica gel cartridges, washed out by water, then derivatized by cysteamine of known (delta)~(13)C value, and the (delta)~(13)C value of its derivative (thiazolidine) determined by GC/C/IRMS. Finally, the (delta)~(13)C value of atmospheric formaldehyde could be calculated by a simple mass balance equation between formaldehyde, cysteamine, and thiazolidine. Using three formaldehydes with different (delta)~(13)C values, calibration experiments were carried out over large ranges of formaldehyde concentrations. The carbon isotope analysis method achieved excellent reproducibility and high accuracy. There was no carbon isotopic fractionation throughout the derivatization processes. The differences in the carbon isotopic compositions of thiazolidine between the measured and predicted values were always <0.5per thousand, within the specifications of the GC/C/IRMS system. The present method was also compared with the previous 2,4-dinitrophenylhydrazine derivatization method, and this method could be performed with lower analytical error and detection limit. Using this method, four 6-h ambient atmospheric formaldehyde samples were consecutively collected from 8 to 9 March 2005. The results showed that the (delta)~(13)C values of atmospheric formaldehyde were different during the daytime and nighttime. This method proved suitable for the routine operation and may provide additional insight on sources and sinks of atmospheric formaldehyde.