Field evaluation of a VOST sampling method

The VOST (SW-846 Method 0030) specifies the use of Tenax{reg_sign} and a particular petroleum-based charcoal (SKC Lot 104, or its equivalent), that is no longer commercially available. In field evaluation studies of VOST methodology, a replacement petroleum-based charcoal has been used: candidate replacement sorbents for charcoal were studied, and Anasorb{reg_sign} 747, a carbon-based sorbent, was selected for field testing. The sampling train was modified to use only Anasorb{reg_sign} in the back tube and Tenax{reg_sign} in the two front tubes to avoid analytical difficulties associated with the analysis of the sequential bed back tube used in the standard VOST train. The standard (SW-846 Method 0030) and the modified VOST methods were evaluated at a chemical manufacturing facility using a quadruple probe system with quadruple trains. In this field test, known concentrations of the halogenated volatile organic compounds, that are listed in the Clean Air Act Amendments of 1990, Title 3, were introduced into the VOST train and the modified VOST train, using the same certified gas cylinder as a source of test compounds. Statistical tests of the comparability of methods were performed on a compound-by-compound basis. For most compounds, the VOST and modified VOST methods were found to be statistically equivalent.