SPECTROPHOTOMETRIC DETERMINATION OF PHENOLIC-COMPOUNDS BY FLOW-INJECTION ANALYSIS

Flow-injection procedures for the spectrophotometric determination of phenol by two different colour reactions have been developed. The common 4-aminoantipyrine (4-AAP) reaction and the oxidative coupling of phenol with 3-methyl-2-benzothiazoline hydrazone (MBTH) are both readily applicable and permit the determination of phenol at a sampling rate of 60 h-1 and a relative standard deviation better than 3%. The sensitivity of the MBTH method is about four times higher than that of the 4-AAP reaction, with detection limits of 12 and 30-mu-g/l phenol, respectively. A study of the responses of the two methods to phenol derivatives revealed particular merits and limitations. The 4-AAP reaction products have similar absorbance maxima but the reactivity is comparatively low. MBTH reacts with several para-substituted phenols and exhibits higher response factors. Because the absorption maxima of the products differ significantly, a problem is the appropriate choice of the measuring wavelength.