Color change behavior of water soluble azo-dye ions in a water-organic solvent mixed medium and its application to a spectrophotometric method for the determination of ethanol.

MOTOMIZU Shoji, HOSOI Yasuhiro, OSHIMA Mitsuko

doi:10.2116/bunsekikagaku.39.4_201

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水溶性アゾ染料イオンの水‐有機溶媒混合媒体中における光吸収変化とエタノールの吸光光度定量への応用
水溶性アゾ染料イオンの水-有機溶媒混合媒体中における光吸収変化とエタノールの吸光光度定量への応用
スイヨウセイアゾセンリョウイオンノミズユウキヨウバイコンゴウ

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Solvent effects on the absorption spectra of water soluble azo-dye ions were investigated. Three types of azo-dyes (Type I, II and III) were used: Type I consists of 4-(4-dialkylaminophenylazo)benzene sulfonate ions (alkyl: methyl, ethyl, propyl and butyl groups), Type II, of 1-alkyl-4-(4-diethylaminophenylazo) pyridinium ions (alkyl: methyl, ethyl and propyl groups) and Type III, of N, N, N-trimethyl-p-phenylazoanilinium ion and its nitro derivative. Of these three types, the Type I dyes showed the most remarkable change in absorption spectrum. The absorption maximum wavelength decreased with increasing alcohol content: the more hydrophilic the dye ion and the alcohol, the greater was the blue shift of the absorption spectrum. This remarkable blue shift is attributed to a change in the contributions of the following resonance forms:<BR>R₂⁺N_??_=N-N-_??_-SO₃^-(A)_??_R₂N-_??_-N=N-_??_-SO₃-(B)<BR>With an increasing alcohol concentration or hydrophobicity around the dye ion, the contribution of the cationic form (A) decreases. By measuring the change in Propyl Orange absorbance at 420 nm, ethanol can be determined. The absorptiometric method of ethanol determination with Propyl Orange was applied to the flow injection procedure.

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BUNSEKI KAGAKU

BUNSEKI KAGAKU 39 (4), 201-205, 1990

The Japan Society for Analytical Chemistry

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