Field method for the determination of insoluble or total hexavalent chromium in workplace air

National Institute for Occupational Safety and Health method 7703 is a portable field procedure for the analysis of workplace air filter samples for hexavalent chromium (Cr-VI) content immediately after the samples are collected. The field method prescribes Cr-VI extraction front air filter samples with an ammonium sulfate/ammonium hydroxide extraction buffer using ultrasonic extraction (UE). Strong anion-exchange solid-phase extraction (SAE-SPE) is then used to separate Cr-VI horn trivalent chromium and other interferences. Portable spectrophotometric measurement of Cr-VI is then conducted using the 1,5-diphenylcarbazide (DPC) method. However, it has been found that the ammonium extraction buffer does not adequately bring insoluble Cr-VI compounds into solution during the UE process. Thus. it was deemed necessary to modify the field method so that it would provide acceptable recoveries for insoluble Cr-VI compounds. To this end, a more alkaline extraction solution-sodium carbonate/sodium bicarbonate buffer-was investigated. The modified procedure using the highly alkaline extraction solution was demonstrated to be compatible with SAE-SPE cartridges when determining insoluble CrVI in air filter samples. It was found that the carbonate/bicarbonate buffer was equally effective for complete dissolution of both insoluble and soluble forms of Cr-VI. Furthermore, the modified procedure met desired performance criteria established for air sampling and analytical methods.