Uric acid hydrogen peroxide determination

Uric acid is usually determined by measuring its ultraviolet absorption at 292 nm. However, the amount of uric acid in blood is small and the absorption is not specific. So, after the measurement, the uric acid is destroyed by adding the enzyme uricase. The absorbance is measured again. The difference in absorbance is due to the uric acid present. Since only uric acid wiU be decomposed by uricase, the method becomes specific. A similar procedure for the colorimetric determination of uric acid involves the oxidation of uric acid with molybdate to form molybdenum blue, a molybdenum(V) compound. In principle, uric acid could be determined as glucose was, but impurities in uricase preparations usually rapidly destroy the very small amount of hydrogen peroxide produced. 

Kamei et al. [45] separated spermine, spermidine, putrescine, and cadav-erine in an ion-pair reversed-phase LC system and detected the hydrogen peroxide formed in the reaction catalyzed by the enzymes putrescine oxidase and polyamine oxidase with POCL. The same analytes were determined in a later study [46], together with the acetyl derivatives. The sensitive determination of uric acid, selectively converted to hydrogen peroxide by uricase, has been investigated by several authors [37, 47],... 

On the other hand, several oxidases are known to generate hydrogen peroxide, acting as an oxidant in the CL system, from corresponding substrates. IMERs in which the oxidases are immobilized on adequate supporting materials such as glass beads have been developed. IMERs are often used for flow injection with CL detection of uric acid and glucose, and are also applicable to the CL determination of acetylcholine, choline, polyamines, enzyme substrates, etc., after online HPLC separation. 

Soc., 1999, 121, 3435 T. Hoshi, H. Saiki, S. Kuwazawa, Y. Kobayama and A. Anzai, Polyelectrolyte multilayer film-coated electrodes for amperometric determination of hydrogen peroxide in the presence of ascorbic acid, uric acid and acetaminophen, Anal. Sci., 2000, 16, 1009 E.S. Forzani, VM. Solis and E.J. Calvo, Electrochemical behavior of polyphenol oxidase immobilized in self-assembled structures layer by layer with cationic polyallylamine, Anal. Chem., 2000, 72, 5300 Y.M. Lvov, Z. Lu, J.B. Schenkman, X. Zu and J.F. Rusling, Direct electrochemistry of myoglobin and cytochrome P450cam in alternate layer-by-layer film with DNA and other polyions, J. Am. Chem. Soc., 1998, 120, 4073. 

Coupling chemiluminescence reactions with immobilized enzymes enables the detection of a variety of substrates. A useful example is oxidase enzymes that generate hydrogen peroxide, which can be quantified with several chemiluminescence systems. Substrates including glucose, cholesterol, choline, amino acids, aldehydes, lactate, and uric acid (reaction [IV]) can be determined at the nanomolar level ... 

Generally, AA is determined individually, and only about a 10% of the published methods determine AA simultaneously with other analytes such as uric acid, glucose, fructose, dopamine, iodate, bromate, hypochlorite, thiourea, glutathione, hydrogen peroxide, acetylsalicylic acid, kojic acid, ascorbyl glucoside, paracetamol, cysteine, and other water soluble vitamins (thiamine [vitamin Bj], folic acid [vitamin B12], niacin [vitamin B3], riboflavin [vitamin B2], and pyridoxine [vitamin B ]). 

The use of mediators to i uce the applied potential in amperometric electrodes, and hence interference, sometimes requires multienzymatic immobilization. Glucose oxidase and peroxidase are cdmmobilized for the determination of glucose without interference firom ascorbic and uric acids. The peroxidase catalyses the reaction of the hydrogen peroxide arising from the oxidation of glucose by the mediator hexacyanoferrate [38]. 

---