KINETIC ENZYMATIC DETERMINATION OF ETHANOL METHANOL MIXTURES BY THE STOPPED-FLOW TECHNIQUE

The analytical use of the enzymatic oxidation of alcohols by alcohol o xidase was assessed applying the stopped-flow technique for mixing sam ple and reagents, and the DTNB (5,5'-dithiobis-(2-nitrobenzoic acid))/ L-cysteine system as a new chromogenic reagent. The oxidation reaction was monitored by measuring the rate of absorbance decrease at 412 nm, the wavelength of maximum absorption of the reduced form of DTNB. The calibration graphs for the individual determination of the alcohols w ere linear over the range 1.0 x 10(-6)-1.0 x 10(-5)M, and the precisio n ranged between 2.1 and 4.8%. A differential rate principle was appli ed to the determination of ethanol/methanol mixtures involving mutual kinetic effects which allowed mixtures in molar ratios between 25:1.0 and 1.0:1.0 to be accurately resolved with good precision (r.s.d. less than 9 and 5%, respectively). Compared to the flow-injection analysis method, the proposed approach offers higher sensitivity and sample th roughput, as well as the wider concentration ratio range for mixture r esolution.