The standard method for the determination of airborne carbonyls is to collect carbonyls onto 2,4-dinitrophenylhydrazine (DNPH) coated solid sorbent followed by solvent extraction of the solid sorbent and analysis of the derivatives using high-pressure liquid chromatography (HPLC). A newly developed approach uses in-injection port thermal desorption (TD) as a sample introduction technique followed by analysis using gas chromatography-mass spectrometry. The principle of this method is to collect carbonyls in air onto sampling tubes packed with Tenax particles, which are pre-coated with pentafluorophenylhydrazine (PFPH). The carbonyls in the form of their PFPH derivatives are desorbed onto a gas chromatography column by heat, finally detected by mass spectrometer. In previous practice, the...[ Read more ]

The standard method for the determination of airborne carbonyls is to collect carbonyls onto 2,4-dinitrophenylhydrazine (DNPH) coated solid sorbent followed by solvent extraction of the solid sorbent and analysis of the derivatives using high-pressure liquid chromatography (HPLC). A newly developed approach uses in-injection port thermal desorption (TD) as a sample introduction technique followed by analysis using gas chromatography-mass spectrometry. The principle of this method is to collect carbonyls in air onto sampling tubes packed with Tenax particles, which are pre-coated with pentafluorophenylhydrazine (PFPH). The carbonyls in the form of their PFPH derivatives are desorbed onto a gas chromatography column by heat, finally detected by mass spectrometer. In previous practice, the coating of solid sorbents with the derivatization agent is achieved by applying solutions followed by drying. This practice inevitably introduces carbonyl impurities in the solvent to the sampling sorbent. In this thesis work, a vapour coating technique has been developed and demonstrated to be superior to the solvent coating approach. The vapour coating technique eliminates the use of solvents during the coating step; thereby reduces background carbonyl contaminants. This technique has a good reproducibility in the amount of PFPH coated in each sampling tube. Lower minimum detection limits were made possible by using this improved coating method.

This newly developed technique has been applied to measure ambient carbonyls in an urban location in Guangzhou, China. A total of 22 carbonyls were positively identified and quantified. An additional 14 carbonyls were tentatively identified on the basis of their mass spectra and relative retention times to known carbonyl compounds. Cooking exhaust, vehicle emission and secondary products were identified to be the main sources. It was found that the two smallest aldehydes, formaldehyde and acetaldehyde, only accounted for less than 40% of OH removal by all the measured carbonyls. This finding indicates the importance of measuring all the significant carbonyls.