Uric acid determination

The enzyme electrodes for determining uric acid monitor reactants or products of the uricase catalyzed reaction ... 

The excreta of stored product insects are composed primarily of uric acid. However, in some species, the presence of other purines in lesser proportions has been reported. Ammonia is found in the excreta of larvae of Ephestia kuehniella, urea and allantoin in Tenebrio molitor, and both urea and xanthin in larval excreta of C. cephalonica (Bursell, 1967). Uric acid has been used as an indicator of insect infestation in cereals and cereal products since the 1950s (Subrahmanyan et al., 1955 Venkatrao et al., 1957). Subsequently, several methods have been described to determine uric acid levels in infested foodstuffs (Table VII). Most of these methods are modifications of tests originally developed for analysis in clinical samples. Pachla et al. (1987) have reviewed the methods of uric acid determination in foodstuffs and biological fluids. 

Manual or automated methods involving uricase enzyme were subsequently developed for use with cereal products (Farn and Smith, 1963b Sen and Smith, 1966). Laessig et al. (1972) used an autoanalyzer, an instrument deployed for determining uric acid in blood, for uric acid analysis in... 

In the blood, uric acid is distributed between red cells and serum. The proportion found in each fraction of the blood is determined by the Gibbs-Donnan equilibrium. Two types of methods are available for determining uric acid in blood—colorimetric and enzymic analyses. The colorimetric methods require preliminary precipitation of blood proteins, which entails coprecipitation of urates. In addition, the color tests are never rigidly specific for urates. For these reasons, accurate uric acid determinations are obtained only by treating the serum with uricase. The disappearance of uric acid from the sample can be determined by a spectrophotometric reading at 292 mp before and after enzymic treatment. 

Blood samples were taken Monday, Wednesday and Friday in the morning before breakfast. Urine samples were collected during 2k hours daily. To check for errors in the urine collection endogenous creatinine in blood and urine were determined. Uric acid was measured by our modification [ ZtJLLNER, I963 ] of the uricase method. 

The test is performed by determining uric acid excretion before and after the administration of pyrazinamide or its metabolite pyrazinoic acid (PZA) in a dosage sufficient to give maximal suppression of uric acid excretion. The decrement in uric acid excretion after PZA administration is taken as a quantitative measure of uric acid secretion. In addition the difference between filtered load of uric acid and uric acid excretion at the time of maximal PZA effect is taken as a quantitative measure of uric acid reabsorption. These estimates of uric acid secretion and reabsorption assume the following conditions (Table 1) ... 

Specific Method for Determining Uric Acid in Serum Using High Perform- 2403. ance Liquid Chromatography and Gas Chromatography-Mass Spectrometry J. Chromatogr. 149 711-720 (1978) CA 89 38949s... 

The enzyme activity was estimated spectrophotometrically at 295 nm by determining uric acid formation (U-32I0 Hitachi) with xanthine as substrate (20). The enzyme reaction system consisted of a I mL reaction mixture containing 0.1 M potassium phosphate buffer pH 7.4, 0.004U XO and xanthine as substrate. All inhibitors were preincubated with enzyme for 3 min, then reaction was started by addition of xanthine. The reference cuvette was identical and only em e was absent. The ICSO and equations of dose-response curves were analyzed by computer with Sigma plot. 

Active immobilized-enzyme used for the production of an oxygen-sensing electrode for determining uric acid Active immobilized enzyme... 

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). 

Along with an effective electrolyte and screening program for genetic disease, the laboratory of Neonatology needs to have the capability of analyzing for other components in blood serum, which aid in the diagnosis of disease. These include such determinations as alkaline phosphatase, and various other enzymes, creatinine, uric acid and a host of other components which are normally assayed by the main clinical laboratory. 

Another procedure which has adequate sensitivity for determining the glucose in 1 microliter of serum of filtrate, is the method which uses copper reduction, and subsequently determination of the cuprous ion with a suitable reagent (15) However, one must be careful that one has obtained complete precipitation, for, if uric acid or any other impurities remain, false high values will be obtained. This would result in disaster for the hypoglycemic infant. To uncover this condition is often one of the major reasons for doing this test. 

The file Is used routinely In the laboratory at the National Institutes of Health In an attempt to explain abnormal test results The resident physicians affiliated with the Clinical Chemistry Service discuss the results with the patient-care physicians and determine If the results were due to the patient s clinical state or to a drug effect This close monitoring of test results has led to recognition of deficiencies In what Is believed are specific enzymatic procedures for the measurement of glucose and uric acid Likewise, the gualac procedure for occult blood In feces was found to yield false negative results under certain circumstances This has prompted the development of a more specific procedure (Jaffe et al unpublished) ... 

Many compounds of biomedical interest, both of endogenous and exogenous origin, are heterocyclic in structure. Many of these compounds are electroactive at potentials useful for LCEC analysis. Methods for the determination of both ascorbic acid and uric acid were developed in the early days of LCEC. The important enzyme... 

Ellerbe P, Cohen A, Welch MJ, and White V E (1990) Determination of serum uric acid by isotope dilution mass spectrometry as a candidate definitive method. Anal. Chem 62 2173-2177. 

Nitrogen compounds commonly determined are creatinine, urea, and uric acid. Creatinine is an end product of the energy process occurring within the muscles, and is thus related to muscle mass. Creatinine in urine is commonly used as an indicator and correction factor of dilution in urine. Creatinine in serum is an indicator of the filtration capacity of the kidney. Urea is the end product of the nitrogen luea cycle, starting with carbon dioxide and ammonia, and is the bulk compoimd of urine. The production of uric acid is associated with the disease gout. In some cases, it appears that the excess of uric acid is a consequence of impaired renal excretion of this substance. 

Although rarely performed, a 24-hour urine collection can be obtained to determine if the patient is an overproducer or an underexcretor of uric acid. Individuals who excrete more than 800 mg of uric acid in this collection are considered overproducers. Patients with hyperuricemia who excrete less than 600 mg/day are classified as underexcretors of uric acid. 

As in the case in the analysis of food samples, the introduction of relatively inexpensive MS detectors for GC has had a substantial impact on the determination of methylxanthines by GC. For example, in 1990, Benchekroun published a paper in which a GC-MS method for the quantitation of tri-, di-, and monmethylxanthines and uric acid from hepatocyte incubation media was described.55 The method described allows for the measurement of the concentration of 14 methylxanthines and methyluric acid metabolites of methylxanthines. In other studies, GC-MS has also been used. Two examples from the recent literature are studies by Simek and Lartigue-Mattei, respectively.58 57 In the first case, GC-MS using an ion trap detector was used to provide confirmatory data to support a microbore HPLC technique. TMS derivatives of the compounds of interest were formed and separated on a 25 m DB-% column directly coupled to the ion trap detector. In the second example, allopurinol, oxypurinol, hypoxanthine, and xanthine were assayed simultaneously using GC-MS. 

HPLC coupled to MS was used for the determination of dimethyl xanthine metabolites in plasma.82 There have also been a number of methods published on the use of HPLC with a PDA detector. In 1996, Mei published a method for the determination of adenosine, inosine, hypoxanthine, xanthine, and uric acid in microdialysis samples using microbore column HPLC with a PDA detector.63 In this method, samples were directly injected onto the HPLC without the need for any additional sample treatment. 

The bimolecular rate constants were determined (Burke 2001) for the repair of carotenoid radical cations by trolox, ascorbic, ferrulic, and uric acids from the pulse radiolysis studies of carotenoids in aqueous micellar solutions (see Table 14.10). 

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],... 

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. 

Modified procedure (ACU kit) The plasma sample is preincubated with uricase (urate oxidase) and then quantified in the ACW assay. The method requires 10 pL of plasma. It is also possible to determine the uric acid (UA) portion in ACW UA = ACW - ACU. 

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