Determination of Uric Acid

Uric acid is the end product of purine metabolism in man. Consequently, abnormal levels of uric acid serve to indicate disorders of metabolism of purines or nucleic acids. Serum levels of uric acid range from 200 to 420 pmol/L In males 15 to 20% and 3 to 4% of females suffer from hyperuricaemia. 

The enzyme used for the assay of uric acid is uricase (urate oxidase, EC 1.7.3.3) which catalyzes the oxidation of uric acid to allantoin, CO2, and H2O2  

The molecular weight of uricase is 100 000. The for uric acid and the pH optimum vary over a wide range depending on the source of the enzyme. 

According to the equation of the reaction, amperometric oxygen or hydrogen peroxide electrodes can be used to follow uric acid conversion. Potentiometric electrodes have seldom been employed because of their slow response (Kawashima and Rechnitz, 1976 Kawashimaetal., 1980). 

In view of the low physiological uric acid concentrations, in the assay of uric acid electrochemical interferences by other anodically oxidizable substances become particularly troublesome. Kulys et al. (1983) coimmobilized HRP with uricase in order to eliminate these interferences. This approach permits uric acid measurement to be performed at a potential of 0 V vs SCE. However, the autoxidation of ferrocyanide used as HRP substrate is a serious drawback of this method. 

---

T. Seki, K. Yamaji, Y. Orita, S. Moriguchi and A. Sliinoda, Simultaneous determination of uric acid and creatinine in biological fluids by column-switching liquid cliromatogra-phy with ulti aviolet detection , 7. Chromatogr. A 730 139-145 (1996). 

Figure 15.14 illustrates a typical voltammetric result for the determination of dopamine in the presence of ascorbic acid with a CNT-modified electrode. The selective voltammetric detection of uric acid [82] or norepinephrine [83] in the presence of ascorbic acid has been demonstrated with a (3-cyclodextrin-modified electrodes incorporating CNTs. Ye et al. [84] have studied the electrocatalytic oxidation of uric acid and ascorbic acid at a well-aligned CNT electrode, which can be used for the selective determination of uric acid in the presence of ascorbic acid. The simultaneous determination of dopamine and serotonin on a CNT-modified GC electrode has also been described [85],... 

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],... 

Sodium tungstate is used in the manufacture of heteropolyacid color lakes, which are used in printing inks, plants, waxes, glasses, and textiles. It is also used as a fuel-cell electrode material and in cigarette filters. Other uses include the manufacture of tungsten-based catalysts, for fireproofing of textiles, and as an analytical reagent for the determination of uric acid. 

Johnson WJ, Chartrand A (1978) Allantoxanamide a potent new uricase inhibitor in vivo. Life Sci 23 2239-2244 Kageyama N (1971) A direct colorimetric determination of uric acid in serum and urine with uricase-catalase system. Clin Chim Acta 31 421-426... 

Electrochemical detection was easily employed for the determination of uric acid in urine, abnormal concentrations of which have been linked to several disease states [14]. A glass/PDMS hybrid device with an off-chip platinum electrode was used to evaluate standard samples for both dopamine and uric acid. The linear responses for dopamine and uric acid were 1-165 and 15-110 pM, respectively, with a 1 pM limit of detection for both. Normal concentrations of uric acid in urine are 800-8000 pM, thus a 50 to 75-fold dilution was used with the urine samples analyzed to place them within the linear range of the detection method. Uric acid concentrations in these urine samples were confirmed using the clinically accepted method. This new method should allow clinical detection of both abnormally high and abnormally low uric acid concentrations in urine samples on a microdevice. 

Plesner, Paul, and Kalckar, Herman M., Enzymic Micro Determinations of Uric Acid, Hypoxanthine, Xanthine, Adenine, and Xanthopterine by... 

Spectrophotometry, Ultraviolet Enzymic Micro Determination of Uric Acid, Hypoxanthine,... 

Ultraviolet Spectrophotometry, Enzyme Micro Determinations of Uric Acid,... 

T12. Troy, R. J., and Purdy, W. C., The coulometric determination of uric acid in serum and urine. Clin. Chim. Acta 27, 401-408 (1970). 

Various methods have been proposed for the simultaneous determination of uric acid and allantoin in different biological matrices. For urine samples, GC-MS was applied for the determination of both compounds. However, HPLC methods are stiU widely accepted. 

Simultaneous determination of uric acid, hypoxan- thine, and xanthine in different biological matrices such asg> urine, urinary calcuh, cerebrospinal fluid, and plasma wa carried out by RP-HPLC with isocratic elution and UVs detection. ... 

Kock, R. Delvoux, B. Tilhnanns, U. Greihng, H. A candidate reference method for the determination of uric acid in serum based on high-performance hquid chromatography, compared with an isotope dilution-gas chromatography-mass spectrometer method. J. Chn. Chem. Clin. Biochem. 1989, 27, 157-162. 

Clearly, the determination of such compounds is crucial for diagnosis and monitoring of renal disease and metabolic disorders. The concentration of oxypurines in blood serum is among the most important parameters in biochemistry and clinical chemistry. Determination of uric acid is performed by enzymatic methods or colori-metrically by reduction of phosphotungstate. 

HPLC methods for the determination of uric acid found in literature include ion exchange, ion-pairing, reversed phase, and size exclusion. Most of these require depro-teinization before analysis, but direct analysis of semm uric acid was also successful by column switching liquid chromatography. 

Seki, T. Yamaji, K. Orita, Y. Moriguchi, S. Shinoda, A. Simultaneous determination of uric acid and creatinine in biological fluids by colunm-switching liquid chromatography with ultraviolet detection. J. Chromatogr., A 1996, 730, 139-145. 

Elin, R.J., Johnson, E. and Chesler, R. (1981). Comparison of four methods for the determination of uric acid with a candidate reference method. Clin. Chem. 27, 1114, Abstr. 465. 

E292 Spain, M.A. and Wu, A.H.B. (1986). Bilirubin interference with determination of uric acid, cholesterol and triglycerides in commercial peroxidase-coupled assays, and the effect of ferrocyanide. Clin. Chem. 32, 518-521. 

E386 Potter, J.L. (1987). Xanthine interference in the Kodak Ektachem determination of uric acid. Clin. Chem. 33,1265. 

R94 Cattozzo, G., Franzini, C., Hubbuch, A.D. and Tritschler, W. (1988). Evaluation of determination of uric acid in serum and whole blood with the Reflotron. Clin. Chem. 34, 414-416. 

Chang, E.S. (1979). A solid phase strip test for the determination of uric acid in serum. Clin. Chem. 25,1091. Abstr. 142. 

A colorimetric method for determination of uric acid was introduced by Folin and Denis (F5) this initial method, which used phospho-tungstate, was modified by a series of investigators (B16, B32, F4). Brown... 

I. Quantitative determination of uric acid in biological fluids. J. Biol. Chem. 211, 149-153 (1954). 

B18. Bergmann, F., and Kalina, M., Determination of uric acid and its thio analogs in biological fluids. And. Biochem. 10, 73-85 (1965). 

P9. Praetorius, E., An enzymatic method for the determination of uric acid by ultraviolet spectrophotometry. Scand. J. Clin. Lab. Invest. 1, 222-230 (1949). 

A.N. Araujo, J.A.M. Catita, J.L.F.C. Lima, Kinetic determination of uric acid in urine based on single-line flow-system with multi-site detection, Anal. Sci. 14 (1998) 809. 

---