Examination of sampling methods for assessment of personal exposures to airborne aldehydes

Abstract

A personal exposure monitor was required for the determination of airborne aldehyde exposures caused by emissions from methanol-fuelled vehicles. Derivatization of aldehydes during collection was selected as the technique to enhance the integrity of samples and to facilitate analysis. Three derivatization agents, HMP [2-(hydroxymethyl)piperidine], BEA (N-benzylethanolamine) and DNPH (2,4-dinitrophenylhydrazine), were examined. High blank levels and poor chromatographic resolution of some of the derivatives discouraged the use of BEA and HMP, whereas DNPH derivatization allowed good sensitivity and resolution of the hydrazones of formaldehyde, acetaldehyde, acrolein, crotonaldehyde and benzaldehyde. Passive and active samplers containing DNPH-impregnated XAD (ORBO-43) and glass-fibre filters were evaluated for the determination of airborne aldehydes at several concentrations in the range 10–5000 µg m^–3. Although analytical detection limits were better than 40 µg m^–3, sampler blank values limited practical detection limits to 50–100 µg m^–3 for the individual aldehydes. The analytical precision relative standard deviation approximately 20%, based on results for samplers deployed in triplicate in a test atmosphere. The effects of humidity, air velocity and concentration of aldehydes on the sampling characteristics of active and passive samplers were measured. Some discrepancies, particularly for the unsaturated aldehydes, were noted for results obtained with the different sampling procedures in controlled-atmosphere chamber tests. These results suggested that, after further development, a DNPH-based passive sampling method could meet the required performance criteria.