On-site screening for benzene in complex environments

A technique is described for on-site screening of workplace atmospheres for benzene in the presence of many potentially interfering substances. The technique allows benzene monitoring with reasonable specificity at the part per million (ppm) level in confined spaces. A commercially available portable gas chromatograph (GC), shown in the laboratory to be capable of resolving benzene from a complex mixture of hydrocarbons, was compared in the field with other portable GCs, sorbent tube samples, and detector tubes. During three field evaluations samples were collected in Tedlar bags, which allowed replicate, on-site analyses by up to three portable gas chromatographs and three types of detector tubes. Additionally, replicate samples were collected from each bag onto charcoal tubes for subsequent laboratory analysis by capillary column flame ionization gas chromatography and by gas chromatography/mass spectrometry. The portable GCs resolved samples to the extent that an integratable response with the retention time of benzene was seen. In some samples this response was not due solely to the presence of benzene, but such instances would overestimate the concentration and provide a more conservative result. The portable GCs had a total analysis time of less than 10 minutes and detected concentrations of benzene below the Occupational Safety and Health Administration's permissible exposure limit of 1 ppm (in most samples, below 0.1 ppm, although the limit of quantitation was matrix dependent). While benzene concentration measurements using detector tubes were less precise, they agreed in almost every instance with the other techniques regarding whether the space was within the 1 ppm "safe for entry" concentration.