Degradation products of Tenax TA formed during sampling and thermal desorption analysis: Indicators of reactive species indoors

Analyses of indoor air samples of semivolatile organic compounds (SVOCs) from five offices in two office buildings, a school classroom, and a room in a day-care center were generally strongly influenced by artifact formation. In the laboratory, the major artifacts could be produced by sampling mixtures of O3, NO2, and limonene in air on the sorbent, Tenax TA. Several SVOCs from O3 degradation of Tenax TA were detected, but only few were identified. The NO2 degradation of Tenax TA analyzed by thermal desorption and gas chromatography (TD-GC) almost exclusively formed 2,6-diphenyl-p-benzoquinone (DPQ) and 2,6-diphenyl-p-hydroquinone (DPHQ). The NO2/Tenax TA reaction could be calibrated, thus the NO2 concentration could be determined simultaneously with a SVOC measurement. However, the results indicated that DPQ may be reduced to DPHQ during TD-GC analysis by oxidation of other compounds adsorbed to Tenax TA. Sampling an air mixture of O3 in excess of limonene on Tenax TA followed by TD-GC analysis exclusively produced DPHQ. O3 alone produced neither DPQ nor DPHQ. It was found that reactive species (possibly Criegee biradicals and/or other organic radicals) from the O3/limonene :reaction were responsible for the production of DPHQ from Tenax TA. The results indicated that Tenax TA can be used as a trapping agent for some radicals by analysis of the DPQ/DPHQ formation. The present data were not sufficient to obtain evidence for degradation of Tenax TA by other radicals than NO and NO2 in indoor SVOC samples. However, the DPQ/DPHQ ratio indicated that DPHQ has been formed from DPQ by oxidation of other adsorbed compounds in some of the samples.