DW-Spectrophotometric Determination of Methanol in Wine with Reagent 5-Br-PADAP

2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) was used as a reagent to recognize the presence of methanol in an ethanolic solution,such as wine.In an ethanolic solution of pH 9.0,absorption maximum (λmax) of 5-Br-PADAP was found at 444 nm and when methanol was present in the solution,the absorption maximum was bathochromically shifted to 552 nm,making a difference of 108 nm in wavelength between the 2 absorption maxima.It was observed in the absorption spectra of ethanolic solution 5-Br-PADAP in the presence of methanol,positive and negative absorption maxima were found at 552 nm and 444 nm respectively,and the values of absorbance,measured at either of the 2 wavelength,were correlated linearly with the concentration of methanol present in the solution.It was proposed that based on facts mentioned above DW-measurement was applied to the determination of methanol in wine,selecting the wavelength 552 nm as the wavelength of determination and 444 nm as the reference wavelength.The proposed method was applied to the determination of methanol in samples of imitated wine and industrial alcohol,giving values of RSD′s (n=8) less than 1%,and values of recovery in the range of 98.7%-100.1%.A discussion on the raction mechanism was also given.