Glucose determination, procedure

We do not use this procedure for glucose, but Figure 37 shows a series of glucose determinations being performed on 25 microliters of blood, illustrating the fact, that with this system, there may be no wash-out from specimen to specimen. 

In uremia there are present in the serum a variety of known and unknown metabolites that can produce aberrant laboratory results. Significant differences in glucose concentration have been observed in such specimens analyzed by ferricyanide (F2a) or Fe (II)-5-pyridylbenzo-diazepin-2-one reduction methods compared to glucose oxidase procedures (K7a). In a patient with elevated creatinine (15 mg/100 ml) and uric acid (10 mg/100 ml), the glucose value determined by the automated alkaline ferricyanide procedure was overestimated by 20 mg/100 ml (C4). In uremic patients undergoing chronic hemodialysis there is a decrease in transaminase activity. In 11 of 19 such patients, there was... 

Fig. 77. Procedure of total glucose determination by external splitting of sucrose by invertase.

The second technique employed for substrate determination is the measurement of the rate of an enzymaticallv catalyzed reaction, as is used to determine enzyme activity. This may take one of three forms. First, the time required for the reaction to produce a preset amount of product or to consume a preset amount of substrate may be measured. Second, the amount of product formed or substrate consumed in a given time may be measured (see Experiment 35 for glucose determination). These are single-point measurements (called end-point measurements) and require well-defined reaction conditions. They are easy to automate or may be performed manually. A third procedure is continuous measurement of a product or substrate concentration as a function of time to give the slope of the reaction rate curve, Ac/Ar. These are the so-called true rate measurements. The measurements must generally be made during the early portion of the reaction where the rate is pseudo first order. 

The evaluation of a procedure for D-glucose determination using hexokinase and D-glucose 6-phosphate dehydrogenase co-immobilized inside a nylon tube has been reported. The practical and economic feasibility of the system for use in a small laboratory was assessed. 

A second principle used widely for glucose analysis, is that of the oxidation of glucose enzymatically, mediated by the action of glucose oxidase with the formation of gluconic acid and hydrogen peroxide (22). In this procedure it is the hydrogen peroxide which is usually assayed for determination of glucose. This method suffers from the action of inhibitors which occur, particularly with patients in a diabetic coma and these need to be removed. 

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) ... 

The determination of the sugar composition was performed with and without prehydrolysis to determine the cellulose content. Cellulose was present in soy meal and in WUS, the content was respectively 17.2 and 17.9 mol%. Both soy meal and WUS contained mainly galactose, glucose (cellulose), arabinose and uronic acids and their sugar compositions were very similar. This indicates that no sugar residues were specifically removed during the isolation procedure. 

There are also RMs which are prepared for a specific application and are used for validation of relevant methods. Cobbaert et al. (1999) made use of Ion Selective Electrode (ISE)-protein-based materials when evaluating a procedure which used an electrode with an enzyme-linked biosensor to determine glucose and lactate in blood. Chance et al. (1999) are involved with the diagnosis of inherited disorders in newborn children and they prepared a series of reference materials consisting of blood spotted onto filter paper and dried, from which amino-acids can be eluted and... 

Potter and co-workers 301) determined reducing sugars in plant materials by reducing copper(II) in alkaline solution to insoluble cuprous oxide and then measuring the excess copper in the filtrate. Mitschell248) conducted further studies on this method. Christian and Feldman 19) have described general procedures for the indirect determination of glucose and of protein. It is anticipated that in the future, we will see many more applications of atomic absorption spectroscopy to the indirect determination of nonmetals. 

Carbohydrate recovered through the elusive analytical procedures were in the range 101% (lyxose, xylose, galactose) to 108% (glucose). Reproducibility data is quoted in Table 4.2. Down to O.lpg of each monosaccharide can be determined in a sample hydrolysate. 

There is increasing interest in the use of specific sensor or biosensor detection systems with the FIA technique (Galensa, 1998). Tsafack et al. (2000) described an electrochemiluminescence-based fibre optic biosensor for choline with flow-injection analysis and Su et al. (1998) reported a flow-injection determination of sulphite in wines and fruit juices using a bulk acoustic wave impedance sensor coupled to a membrane separation technique. Prodromidis et al. (1997) also coupled a biosensor with an FIA system for analysis of citric acid in juices, fruits and sports beverages and Okawa et al. (1998) reported a procedure for the simultaneous determination of ascorbic acid and glucose in soft drinks with an electrochemical filter/biosensor FIA system. 

Enzymes play an important role in biochemical analysis. In biological material—e. g in body fluids—even tiny quantities of an enzyme can be detected by measuring its catalytic activity. However, enzymes are also used as reagents to determine the concentrations of metabolites—e.g., the blood glucose level (C). Most enzymatic analysis procedures use the method of spectrophotometry (A). 

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