Volatile Organic Compounds from Tenax®/Tenax®/Anasorb®-747 Tubes by the SMVOC Sampling Method
These methods describe the sampling (0031), desorption (5041A), and analysis (8260B) of volatile organic compounds collected from stack gas effluents using volatile organic sampling train (Super-VOST) methodology. This method is also referred to as the SMVOC method (sampling method for volatile organic compounds). Samples are analyzed by thermal desorption of the sorbent tubes followed by GC/MS analysis. For this method volatile organic compounds are defined as those compounds with boiling points in the range of -15°C to 121°C. Although this method is not applicable for polar, water soluble and reactive volatile organic compounds.
Samples are collected using a SMVOC sampling train consisting of a heated probe, water cooled condensers, Tenax®/Tenax®/Anasorb®-747 sorbent tubes, an empty impinger for condensate collection, and a silica gel drying tube. Isokinetic conditions are not required for sample collection since the compounds of interest are in the vapor phase at the point of sample collection. The upper concentration limit for volatile organic compounds in the effluent stream is 1.5ppm per the method.
20L is the recommended sampling volume for collection and there are two recommended sampling rates referred to as FAST-VOST and SLO-VOST. The sampling rate is 1 L/min. by the FAST-VOST method and 0.25 L/min. for 20 min. or 0.5 L/min. for 40 min. for the SLO-VOST method. The goal of either method is to collect a total number of sorbent tube sets to encompass a total sampling time of 2 hours (one ‘run’): i.e., if a sampling rate of 1L/min for 20 minutes is used, a total of six sorbent tube sets will be collected in 2 hours of sampling.
When sampling for a compliance project, 3 runs as described above are collected Analysis of the condensate collected in the empty impinger of the sampling train is also typically required for compliance projects. The two Tenax® tubes typically will be analyzed in tandem with the Anasorb®-747 tube analyzed separately, although all three tubes may be analyzed individually or in tandem per guidance from the overseeing regulatory body. Lower detection limits are achieved by combining all the tubes for analysis. The method also states that it's acceptable to collect the condensate at the end of each 2 hour run.
The method also requires the collection and analysis of a field blank and trip blank per sampling event. A trip blank consisting of a set of Tenax®, Tenax®, Anasorb®-747 tubes from the same lot number and kept under the same conditions from the time the tubes leave the laboratory until they return to check for contamination from shipping and handling.
High moisture sources may cause problems with the analyses as the moisture will dampen the Tenax® and Anasorb®-747 sorbents. It is difficult to purge the POHCs from wet sorbents resulting in poor desorption efficiencies.
NOTE: SW-846 Method 5040 has been replaced by SW-846 Method 5041A, and SW-846 Method 8240 has been replaced by SW-846 Method 8260B.