National Institute for Occupational Safety and Health

“ Tygon tubing has been shown to adsorb some materials in complex hydrocarbon mixtures and to off-gas during later sample collection causing an increase in hydrocarbon concentration in those subsequent samples. (3) Pump the air sample into the bag at a rate calculated to fill ≤80% of the sample bag capacity over the sampling period. NOTE: The flow rate must be constant throughout the sampling period. (4) Within 4 h after completion of sampling, introduce an aliquot of the sample into the GC (as in step 2.a) . Obtain the benzene peak height or area of the injected sample. ”

“ Alternatively, purge used bags at least two times with clean air, then fill with clean air and analyze for benzene as in step (4) below. (2) Attach the sample bag to the outlet port of a personal sampling pump with a minimum length of flexible tubing. To the inlet port of the pump attach a length of Teflon tubing sufficient to reach the desired site. Alternatively, a rubber squeeze bulb can be used in place of a personal sampling pump when sample size is small. In either case, tubing and pump/bulb should be flushed with sample air prior to, and clean air subsequent to, sample collection. ”

“ To reduce the possibility of contamination, use separate, previously unused syringes for working standards and samples. Test syringes for contamination occasionally by filling them with clean air and analyzing the contents. ”