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IS HCI THAT IS USED AS A PRESERVATIVE CREATING FALSE POSITIVES FOR TBA IN GROUND WATER
Citation:
Wilson*, J T. IS HCI THAT IS USED AS A PRESERVATIVE CREATING FALSE POSITIVES FOR TBA IN GROUND WATER. Presented at LUST Conference, San Francisco, CA, March 09 - 12, 2003.
Impact/Purpose:
To inform the public.
Description:
Will hydrochloric acid produce false positives for TBA? Yes, if you heat the sample to get a lower detection limit for TBA. Conventional purge and trap methods at ambient temperature have a reporting limit for TBA between 50 and 100 g/liter. This is higher than the provisional action goal for the State of California (12 g/liter) and near the cleanup goal for the State of New York (50 g/liter). The preferred method to achieve more sensitivity for TBA is to heat the water sample to 80 degrees Celsius during purging. Traditionally, ground water samples from LUST sites are preserved by adding hydrochloric acid to a pH less than 2. If the water is heated during purging, from 20% to 80% of the MTBE originally present in the sample can be hydrolyzed to TBA during analysis. This analytical artifact produced false positives in a study of the distribution of TBA in a plume on Long Island, New York. Hydrolysis produced concentrations of TBA above 1,000 g/liter, when the true concentrations in the aquifer were less than 6 g/liter. Hydrolysis can be avoided if the samples are preserved with a base (such as trisodium phosphate), or if the samples are neutralized before analysis. The rate of acid hydrolysis is very sensitive to temperature. If samples preserved with hydrochloric acid are stored at 4 degrees Celsius for up to four weeks, less than 1% of the MTBE will be hydrolyzed to TBA.