The Determination of Background Levels of Volatile Organic Compounds in Atmosphere

Year 2001, Volume: 3 Issue: 1, 125 - 147, 01.06.2001

Marjan Weber M. Pompe H. Basa

Abstract

Volatile organic compounds (VOCs) of anthropogenic as well as biogenic origin play an important role in different photochemical processes in the troposphere. In order to evaluate their impact on ozone formation processes, a detailed knowledge about their abundance in the atmosphere is required. There are several different analytical methods available for the determination of background levels if VOC in the air. Sampling can be performed either collecting the whole sample (e.g. canister, bags) or by preconcentration on absorption tubes or cold traps. For their determination gas chromatography using different detectors (FID, ECD, MSD) is applied. The absorption tubes filled with different adsorption materials (i.e.Tenax, Carbotrap, Carbosieve,) to collect VOC from C to Capplied and the absorption efficiency of individual absorbents was tested. Special attention was dedicated to the sampling of biogenic compounds.
The samples were cryo-refocused after thermal desorption and
injected on gas-chromatographic capillary column. Two separation
methods were developed. The first one includes separation of C2 to C10
isomers using nonpolar OV-1 column. Baseline separation of C2
isomers was obtained by cooling the chromatographic oven to -60o C. To avoid multiple overlapping of chromatographic peaks two-column
system was developed. While Al2O3/KCl PLOT column was used for
the separation of high volatile VOCs (C2 to C6) lower volatile VOC
were separated using nonpolar DB-5MS column. The identification of VOC was performed
using several standards and MS detector, while quantitative results were
obtained with FID detector.
Since unspecific fragmentations in the homologous series can
hinder identification of the unknown substances during gas
chromatographic separation coupled with mass spectrometry, some
chemometric approaches have been introduced to solve this problem.
The accuracy of the developed methods was performed by comparison
of results obtained by different laboratories during field measurements.