Novel absorbance peak of gentisic acid following the oxidation reaction.

Sho Hosokawa,Yasunori Tokuhara,Kenichi Shukuya,Hiroyuki Ohsaki,Eiichiro Hirakawa,Keisuke Sogabe,Yasukazu Ejima,Tatsuo Shimosawa,Tatsuya Morinishi,Maria Gasset

doi:10.1371/journal.pone.0232263

Abstract

Gentisic acid (GA), a metabolite of acetylsalicylic acid (ASA), and homogentisic acid (HGA), which is excreted at high levels in alkaptonuria, are divalent phenolic acids with very similar structures. Urine containing HGA is dark brown in color due to its oxidation. We recently reported a new oxidation method of HGA involving the addition of sodium hydroxide (NaOH) with sodium hypochlorite pentahydrate (NaOCl·5H2O), which is a strong oxidant. In the present study, we attempted to oxidize GA, which has a similar structure to HGA, using our method. We herein observed color changes in GA solution and analyzed the absorption spectra of GA after the addition of NaOH with NaOCl·5H2O. We also examined the oxidation reaction of GA using a liquid chromatography time-of-flight mass spectrometer (LC/TOF-MS). The results obtained indicated that GA solution had a unique absorption spectrum with a peak at approximately 500 nm through an oxidation reaction following the addition of NaOH with NaOCl·5H2O. This spectrophotometric method enables GA to be detected in sample solutions without expensive analytical instruments or a complex method.

Highlights

Gentisic acid (2,5-dihydroxybenzoic acid, GA), one of the metabolites of acetylsalicylic acid (ASA), is excreted into the urine in excessive amounts under various conditions [1]
homogentisic acid (HGA) is excreted at excessive amounts in the urine of patients with alkaptonuria, which is a hereditary metabolic disorder causing the accumulation of HGA
Regarding GA solution treated with more than 200 mg/L ascorbic acid (AA), color changes were not recognized by the naked eye before or after the reaction

Summary

Introduction

Gentisic acid (2,5-dihydroxybenzoic acid, GA), one of the metabolites of acetylsalicylic acid (ASA), is excreted into the urine in excessive amounts under various conditions [1]. GA is a divalent phenolic acid with a similar structure to homogentisic acid (2,5-dihydroxyphenylacetic acid, HGA) (Fig 1). HGA is excreted at excessive amounts in the urine of patients with alkaptonuria, which is a hereditary metabolic disorder causing the accumulation of HGA. Alkaptonuric urine containing HGA turns dark brown in color when left to stand due to the oxidation of HGA to benzoquinone acetic acid (BQA) [2].

Methods

Results

Conclusion