In addition, the quality assurance and quality control
(QA/QC) procedure included field blanks, parallel samples and
duplicate measurements of samples. During the sampling procedure,
one sampling tube was opened at the sample site and then the
ends capped, which served as a blank. The blank sample was transported
along with the sampling tubes to the sampling points, stored
in the laboratory during the exposure period, and later analyzed to
ensure that there was no contamination from sample collection,
transportation or storage. The blank was tested with no significant
contamination found for any of BTEX species. The performance of
the entire analytical system was checked by means of analyzing
blanks and tubes with known analyte concentrations