ANALYSIS AND STABILITY OF ALDEHYDES AND TERPENES IN ELECTROPOLISHED CANISTERS

Aldehydes and terpenes are important classes of polar VOC contaminants for which few sampling and analysis methods have been validated. This study reports on the analysis, stability and recovery of seven aldehy des (butanal, pentanal, hexanal, heptanal, octanal, nonanal and benzal dehyde) and four terpenes (alpha-pinene, beta-pinene, limonene and 3-c arene) prepared at trace levels (3-5 ppb) and stored in electropolishe d stainless-steel canisters. Humidified air, humidified N-2, and dry a ir were used to dilute three sets of canisters. A series of samples wa s withdrawn from each canister over a period of 16 days, and concentra tions were determined by cryogenic preconcentration, gas chromatograph y and mass spectrometry. The VOCs were easily separated, but butanal a nd pentanal had high detection limits relative to the other compounds. While measurements were reproducible, concentrations decreased consid erably in the first hour(19% in the humidified air-filled canister set ), and losses continued over the measurement period, although at a slo wer rate. The estimated half lives of aldehydes and terpenes were 18 d in humidified air-filled canisters, 24 d in humidified N-2, and 6 d i n dry air. Loss mechanisms and analytical considerations for the targe t compounds are discussed. Like other VOCs, the collection and storage of aldehydes and terpenes in canisters require humidification; howeve r; the absolute accuracy of samples and standards of mixtures of aldeh ydes and terpenes stored in canisters may be limited. (C) 1998 Elsevie r Science Ltd. All rights reserved.