Direct and simultaneous determination of trace-level carbon tetrachloride, peroxyacetyl nitrate, and peroxypropionyl nitrate using gas chromatography-electron capture detection
Résumé
Gas chromatography equipped with electron capture detector (GC-ECD) has been widely used for detecting atmospheric peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN). However, to the best of our knowledge, only a few capillary columns have been adopted for separation to achieve the direct and simultaneous analysis of the two atmospheric pollutants. This paper demonstrates a novel method for directly and simultaneously measuring atmospheric carbon tetrachloride (CCl4), PAN, and PPN using GC-ECD with a DB-1 separation column. The responses of the GC-ECD to PAN, PPN, and CCl4 were individually calibrated by using gas mixtures prepared via volatilization of synthesized solutions of PAN and PPN or high-purity CCl4 reagent in a Teflon Bag. The concentrations of PAN and PPN in the synthesized solutions were quantified by ion chromatography (IC). Further calibration of the GC-ECD for PAN was conducted by in situ photochemical formation of gaseous PAN which was quantified by a NOx analyzer. The two calibration methods agreed well with each other, and the overall uncertainties for measuring atmospheric PAN were estimated to be ±13% and ±15% based on the calibrations of IC and NOx, respectively. The detection limits (three times the signal to noise ratio) for PAN, PPN, and CCl4 were estimated to be 22, 36, and 5 pptv (parts per trillion by volume), respectively. The atmospheric concentrations of these compounds were measured for several days in August in Beijing, and the values obtained in this study were found to be in good agreement with the data reported in the literature for Beijing using other GC-ECD methods.