Abstract
There is a growing interest in the characterisation of volatile organic compounds (VOCs) in workroom air because of the potentially adverse health effects of these compounds. Volatile organic compounds have intrinsic properties as they vaporise easily and penetrate deep into the lungs were they can be transported to a number of target organs.
The VOCs selected for this study were methylethylketone, methylisobutylketone, benzene, toluene, perchloroethylene, butylacetate, decane, limonene, a- and b-pinene. An investigation of the selected VOCs on the solid adsorbents Tenax TA, Chromosorb 106 and Carbotrap has been carried out regarding method optimalisation (conditioning, desorption, calibration), blanks, blank build-up, storage stability (50 ng and 500 ng at 5 ºC and 20 ºC) as a function of time, intercomparison in a field study and detection limit. The analytes were introduced into the gas chromatograph by means of thermal desorption and detection was performed by mass spectrometry.
For the optimalisation of the adsorbents regarding conditioning- and desorption procedures it was established that complete desorption could be achieved for all adsorbent-adsorbate combinations. Linearity, with regression coefficient of 0.99 or better, was established in the mass range 1 1500 ng with low relative standard deviations (RSD) in the calibration application. The blank levels and the blank build up on Carbotrap and Tenax TA have been investigated and found to be excellent with no signs of artefact development over time. Chromosorb 106, however, contains inherently more artefacts that build up over time.
The stability of the analytes on the adsorbents over time was investigated and it was found that Chromosorb 106 gave the overall best results with recoveries of 90 % or better for all analytes. Tenax TA and Carbotrap gave lower recoveries and were more influenced by variations in time, temperature and concentration. Refrigerated temperatures are best avoided for storage on Tenax TA but may increase the recovery of some compounds (e.g. butylacetate) on Carbotrap.
A system for comparing solid adsorbents in a diffusive sampling mode was constructed for field-sampling. Active charcoal sampling with solvent desorption was used as a reference method. The atmospheric concentrations of a-, b-pinene and limonene in an insect repellent production facility were investigated and relative good agreement between the adsorbents and the charcoal samples were found. Chromosorb 106 gave somewhat higher results compared to Tenax TA, while Carbotrap gave the lowest results. Tenax TA gave results that were most consistent to those found on charcoal.
The limits of detection (LOD) and quantification (LOQ) of the analytical system were determined for the selected analytes, and rang from 0.01 - 0.05 ng and from 0.03 - 0.15 ng respectively. This equals a LOD and LOQ for 8 hours diffusive sampling of approximately 0.03 - 0.35 µg m-3 and 0.09 - 0.69 µg m-3 respectively, for all adsorbents. In comparison, the LOD for 8 hours active sampling were between 0.4 2.1 ng m-3.