Rapid aqueous sample extraction of volatile organic compounds: effect of sample matrix and analyte properties

Studies have been done using a rapid aqueous sample extraction (RASE) system to characterize the effects of chemical properties on the time required for removal of volatile organic compounds (VOCs) to the gas phase. These analyses include determinations of the effects that different analytes, and modifications to the matrix, have on extraction time. Experiments were performed to determine the distinct contributions of analyte removal from water and gas-phase transport to the duration of the extracted pulse of analytes. These measured durations were correlated with known values of Henryʹs law constants (KH), boiling points, relative volatilities from modified matrixes, and aqueous diffusion coefficients for cyclohexane, toluene, o-xylene, isopropylbenzene (IPB), and o-dichlorobenzene. Transport time, which was the most significant contributor to the overall duration, correlated well with analyte boiling point. Analyte removal from water correlated better with a modified relative volatility measurement than either KH or DL. IPB extraction was studied in a number of modified matrixes. A 0.1% methanol in water matrix resulted in a 35% decrease in the extraction time of IPB relative to pure water. Extraction time decreased by 22% with the addition of 0.1% NaCl to the aqueous matrix. The addition of 0.01% sodium dodecyl sulfate to the matrix resulted in a 13% increase in the extraction time of IPB relative to water. The RASE system was directly interfaced to a cryofocussing high-speed gas chromatography system to analyze VOCs in wastewater at the low μg l−1 level.