Freon FC-113, an alternative to methylene chloride for liquid—liquid extraction of trace organics from chlorinated drinking water

Abstract

Methylene chloride is the U.S. Environmental Protection Agency solvent of choice for the liquid—liquid extraction of base-neutral organic compounds from water. The presence of cyclohexene as a preservative in the methylene chloride becomes a serious constraint when a 10 5 concentration factor is needed to isolate ng/l amounts of the trace constituents for biological testing ( e.g. Ames bioassay) and/or gas chromatographic (GC) and GC—mass spectrometric (MS) analysis of chlorinated water samples. Cyclohexene reacts with the residual free chlorine in the samples to produce many chlorinated and oxidized cyclohexene products. These artifacts mask large portions of the early chromatogram (Kovats index < 700–1300) of a capillary GC analysis on a non-polar stationary phase. Also, dechlorination by a reducing agent can affect any electrophiles present in the sample which are analyzed in the Ames procedures. This study evaluates the replacement of methylene chloride with freon FC-113 for the isolation of trace organics from chlorinated water samples that will be used for biological testing and/or GC and GC—MS analysis. Freon was found to minimize the interferences from solvent artifacts. A continuous liquid—liquid extractor is used to compare the extraction efficiency of methylene chloride and freon. The results showed that the extraction efficiency of both solvents are comparable when 100–300 ng/l of non-polar organics are extracted and concentrated 1000-fold. Solvent blanks showed freon to have no contaminants at 200-fold concentration and, when used to extract chlorinated water, no byproducts were observed. Field sampling and quality assurance considerations show that freon is an acceptable alternative to methylene chloride for the isolation of trace organic compounds when large volumes of chlorinated waters are concentrated 10 5-fold for toxicity testing or GC and GC—MS analysis.