Periodate-catalyzed oxidative coupling of aniline-derived P-aminophenol with P-xylenol as a detection method for hydroxyl radicals

A simple spectrophotometric method for rapid detection of hydroxyl radical ((OH)-O-.) has been developed. The principle of the method depends upon the hydroxylation of a trapping agent, aniline, by (OH)-O-. leading to the for mation of various hydroxylated products. One of these hydroxylated products , p-aminophenol (PAP), is capable of undergoing an oxidative coupling react ion with p-xylenol (2,5-dimethylphenol) catalyzed by sodium periodate. The resultant indophenol-derivative formed can be measured spectrophotometrical ly at 635 nm. The net increment of absorbance at 635 nm can then be used to estimate the degree of hydroxylation of aniline, which is dependent upon t he amount of (OH)-O-. present in the assay system. A specific example for e stimating the (OH)-O-.-scavenging abilities of food products is also given.