Determination of ambient ethanol concentrations in aqueous environmental matrixes by two independent analyses

A new method for the determination of ethanol in aqueous environmental matrixes at nanomolar concentrations is presented and compared to an existing method that has been optimized for low-level alcohol determinations. The new analysis is based upon oxidation of ethanol by the enzyme alcohol oxidase obtained from the yeast Hansenula sp. which quantitatively produces acetaldehyde after reaction for 120 min at 40 °C and pH 9.0. The acetaldehyde reacts with 2,4-dinitrophenylhydrazine forming a hydrazone that is separated from interfering substances and quantified by high-performance liquid chromatography (HPLC) with UV detection at 370 nm. Comparison of initial acetaldehyde concentration with that after enzymatic oxidation yields the ethanol concentration with a corresponding detection limit of 10 nM. Analytical results were verified by intercomparison with a completely independent technique utilizing a solid-phase microextraction (SPME) Carboxen/PDMS SPME fiber. A 12 mL aqueous phase sample was heated at 50 °C for 10 min prior to loading onto the SPME fiber. Extraction of ethanol was performed by introducing the fiber into the headspace above a pH 4.4 buffered sample containing 30% NaCl for 20 min. Samples were agitated during heating and extraction by magnetic stirring at a rate of 750 rpm. The fiber was thermally desorbed for 1 min at 230 °C in the injection port of a gas chromatograph equipped with a flame ionization detector (FID) set at 250 °C. The resulting ethanol detection limit is 19 nM. Results of an intercomparison study between the enzymatic and SPME analyses produced a trend line with a slope of unity demonstrating that methods produced statistically equivalent ethanol concentrations in several natural waters including rainwater, fresh surface waters, and sediment pore waters.