On-line multi-bed sorption trap for VOC analysis of large-volume vapor samples: injection plug width, effects of water vapor and sample decomposition

Abstract

A multibed on-line sorption trap is used to preconcentrate organic vapors from air samples and inject the analytes into a GC separation column. Injection plug widths depend on the boiling point for the lipophilic compounds and on the polarity and boiling point for the polar compounds. Injection plug widths are sufficiently small (0.7-0.8 s) as to allow the direct injection of the most volatile compounds into the GC column without the need for a second focusing device. The presence of water in the samples has an effect on the retention of polar compounds by the trap. However, this effect is reproducible for a fixed water content and so can be overcome by using calibration standards under the same conditions of humidity as the samples. The thermal decomposition of many volatile organic compounds in an on-line sorption trap during the GC analysis of air samples is examined. The results show that degradation of unstable compounds is governed by the amount of heat transferred to the compounds during desorption (i.e., applied temperature and pulse duration). The use of an on-line trap results in the immediate transfer of desorbed compounds to the analytical column, which can reduce the formation of artifacts.

Capillary thermal desorption unit for near real-time analysis of VOCs at sub-trace levels. Application to the analysis of environmental air contamination and breath samples

“…A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 12 Similar trap configurations to the one used in this study have previously been described using four-bed [17,20] and three-bed configurations [14]. The use of a three-bed trap is adequate for the analysis of breath samples and a previous study has managed to detect more than 250 VOCs using this configuration [14].…”

“…A desorption temperature around 300ºC has been found to be sufficient to obtain adequate bandwidths [17], which also helps to prevent thermal degradation of the most reactive VOCs [20].…”

“…This process has two main disadvantages. First, the use of two traps and two heating processes increases the formation of artifacts and many compounds can be formed during the heating process, which may lead to the detection of compounds that are not present in the original sample [20]. Second, the use of a cryotrap increases the complexity of the 10 instrumentation and makes it necessary to use cryogenic gases, which complicates the development of portable instruments based on this configuration.…”

“…Second, the use of a cryotrap increases the complexity of the 10 instrumentation and makes it necessary to use cryogenic gases, which complicates the development of portable instruments based on this configuration. It has been demonstrated that it is possible to develop miniaturized TD modules without the use of cryogenic traps, which allow the direct injection of the retained VOCs in the multibed trap into a GC column [17,20,21]. When using this simplified configuration, the formation of artifacts due to thermal oxidation reactions in the surface of the sorbents is reduced and more reproducible results can be obtained [20].…”

Characteristics of the Major Atmospheric Aromatic Hydrocarbons in the Yellow Sea

“…Measurements using the adsorbent method are particularly vulnerable to various artifacts (Sanchez and Sacks, 2004;McClenny et al, 2002). Thus, it is necessary to assess the quality of measurements before further data analysis.…”