Novel absorbance peak of gentisic acid following the oxidation reaction.

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.

Absorbance measurements of oxidation of homogentisic acid accelerated by the addition of alkaline solution with sodium hypochlorite pentahydrate.

The urine of patients with alkaptonuria turns dark brown due to the oxidation of homogentisic acid (HGA) to benzoquinone acetic acid (BQA), and this is accelerated by the addition of alkali. We recently reported that alkaptonuric urine and HGA after the addition of alkali showed characteristic peaks at 406 and 430 nm. In order to improve the sensitivity of our spectrometric method for the detection of HGA, we accelerated the oxidation of HGA to BQA using sodium hypochlorite pentahydrate (NaOCl·5H2O), which is a strong oxidant. In the present study, we measured the absorption spectra of alkaptonuric urine and HGA solution after the addition of sodium hydroxide (NaOH) or NaOH with NaOCl·5H2O and analyzed the oxidation reaction of HGA after alkalization using a liquid chromatography time-of-flight mass spectrometer (LC/TOF-MS) and nuclear magnetic resonance (NMR) spectrometry. We accelerated the oxidation of HGA to BQA by adding NaOH with NaOCl·5H2O, and this absorbance measurement was useful for more sensitively observing the oxidation of HGA than LC/TOF-MS and NMR spectroscopy. This quick and easy screening method may be suitable for the diagnosis of alkaptonuria.

Decomposition procedure using methyl orthoformate to analyze silicone polymers.

A new decomposition method for structural analysis of polysiloxanes (silicones) was developed using methyl orthoformate. The siloxane bonds in samples with vinyl and/or methyl side groups decomposed under relatively mild acidic conditions up to around 70°C and were followed by methoxylation at the cleaved linkages with few side reactions. The product yields with respect to the siloxane monomer units were 98-100% for low molecular weight model siloxane compounds. Additionally, this method decomposed the silicone polymer sample in a similar manner with decomposition yields of 98 and 103% for the dimethylsiloxane main chain and dimethylvinylsilyl end groups, respectively. These results demonstrate that the proposed decomposition method should be an effective pretreatment procedure for structural and compositional analyses of silicone polymers.