Feasibility of collection and analysis of airborne carbonyls by on-sorbent derivatization and thermal desorption.
The most commonly used method for analysis of airborne carbonyls is to collect the analytes on solid sorbents coated with a suitable derivatization agent, followed by solvent desorption and liquid injection for analysis by high-pressure liquid chromatography. We have explored a new approach by combining on-sorbent derivatization and thermal desorption to measure airborne carbonyls. More specifically, carbonyls in the air are collected onto an O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA)-coated Tenax sorbent packed in a tube with dimensions identical to those of a gas chromatography (GC) injector liner. The derivatives are then released by in-injection port thermal desorption to a GC column for analysis. Gaseous carbonyls, including formaldehyde, acetaldehyde, benzaldehyde, glyoxal, and methylglyoxal, at ppbv levels are shown to be effectively collected (> or = 92% collection efficiency) onto the sampling tubes at a flow rate of 20 mL/min under both < 1% and 71% relative humidity. The collection efficiency drops as the sampling flow rate increases, and the degree of decrease is compound dependent. The derivatization agent, at a level of approximately 127 nmol/tube, is thermally desorbed and eluted from the GC column without compromising the determination of any carbonyl-PFBHA derivatives. Detection limits of low ppbv to sub-ppbv are achieved for a sample air volume of 4.8 L. Using this new method, we have measured formaldehyde, acetaldehyde, benzaldehyde, glyoxal, and methylglyoxal to be 4.9-16.3, 0.6-8.2, <5.9, 0.5-4.1, and <2.4 ppbv, respectively, in the ambient atmosphere at the university bus stop. This method is less labor intensive than the solvent desorption technique and avoids use of organic solvents. Other classes of airborne polar species can be measured through the same approach by selecting an appropriate derivatization agent.
Ho
StevenSaiHang
S
Department of Chemistry, Hong Kong University of Science & Technology, Clear Water Bay, Kowloon.
Yu
Jian Zhen
JZ