Environ. Sci. Technol. 1992, 26, 160-163
Concentration of Water-Soluble Volatile Organic Compounds from Aqueous Samples by Azeotropic Microdistillation Mark L. Bruce," Richard P. Lee, and Marvin W. Stephens
Wadsworth/ALERT Laboratories, Inc., 4101 Shuffel Drive N. W., North Canton, Ohio 44720 Methanol and other similar water-soluble volatile organic compounds in zero headspace extracts and other aqueous matrices can be analyzed by azeotropic microdistillation, followed by gas chromatographic separation and detection. The method detection limits for methanol, l-butanol (n-butyl alcohol), and 2-methyl-l-propanol (isobutyl alcohol) are at least 1 order of magnitude below the current land disposal treatment standards using the toxicity characteristic leaching procedure (TCLP). A microdistillation system was developed to address the limitations of direct sample injection, purge-and-trap, and other azeotropic distillation systems. Sample volume requirements range from 10 to 40 mL. The concentration factors range from 70 to 230 (depending on the analyte) with a 40-mL sample. The total distillation time is -5 min. Typical detection limits are between 5 and 15 pg/L when the distillate is analyzed by gas chromatography with flame ionization detection. Introduction The Hazardous and Solid Waste Amendments of 1984 amended the Resource Conservation and Recovery Act (RCRA) by banning all land disposal of untreated hazardous waste within 5l/, years after passage. The basic purpose of the land disposal restrictions is to discourage activities that involve placing untreated wastes in or on the land when a better treatment or destruction alternative exists. Under the land disposal restrictions (40 CFR part 268.41) for spent solvents, methanol has a treatment standard of 0.25 mg/L for wastewaters containing spent solvents and 0.75 mg/L for all other spent solvent wastes in the waste extract using zero headspace extraction (ZHE). To date there are no EPA-approved methods for methanol that have detection limits below these treatment standards. The effect of this void is that residues from the treatment of solvent wastes and multisource leachate wastewaters cannot presently be certified to meet the corresponding treatment standards and thus cannot be landfilled. Conventional direct sample injection did not provide adequate analyte detection limits because there was no concentration step. In addition, direct sample injection deposited nonvolatile sample constituents in the chromatographic system, which degraded performance. This was particularly true for zero headspace extracts. Purge-andtrap sample introduction did not meet the detection limit requirements because the analytes were very water soluble and thus difficult to purge. Absolute analyte recovery was very low (typically 50% analyte. If the azeotrope is
