Evaluation of potential sample contamination from a self-designed automatic device for volatile organic compounds...

Monitoring volatile organic compounds using active sampling require from precise samplings during definite periods of time. The sampling strategy has to fulfil several aspects: be representative, simple to use, no degradation and losses must occur during sampling, storage and analysis, and no contamination must result during sampling. Several experiments were carried out for the evaluation of possible sampling contamination in self-designed active samplers that use sorbent tubes for VOCs collection. These sampling devices are composed of two valves at each extent of the sampling tube, allowing the air pass through the tube during sampling and preventing it when not sampling. Three types of valves were evaluated for possible VOC contamination through diffusion: two types of non-return valves and a solenoid valve. Sorbent tubes were connected to the different valves during 15 days and placed in a neutral office environment. Additionally, the same amount of blank tubes was placed near the tubes connected to the valves, in order to determine background contamination. Results showed that non-return valves #1 and #2 emitted non-negligible amounts of aromatic hydrocarbons, ethers and siloxanes, showing values of 200±36 ng and 154±37 ng, 55±14 ng and 35±14 ng, and 169±60 ng and 554±320 ng, per tube respectively. On the other hand, solenoid valves were the ones showing less contaminated tubes, as VOCs profiles observed in the sampling tubes were very similar to the ones from the blank tubes, showing mainly a contribution of the most volatile compounds present in the environment where the experiments took place.