Amperometric detection glutamate

This allows the combination with the amperometric detection of hydrogen peroxide. However, if glutamine and glutamate are simultaneously present in a sample, a differential measurement is required. 

Photometric determinations with p-chloromercuribenzoate (3) were carried out in phosphate at pH 8 27 1SH groups were found per mole of unmodified and also of acetyl glutamate-activated carbamyl-P synthetase. With cold-inactivated enzyme, however, only 19 to 20 groups could be detected. The same results were obtained by amperometric titration in aqueous solution (2) and in 8M urea (5) after sulfitolysis on the cold-inactivated enzyme, an average of 23 SH groups per mole of enzyme was determined. The cases thus far examined, of substrate-induced enzyme inactivation, show also a change in SH group content (1, 14). 

The catalytic detection of ammonium ions has not been extensively investigated in contrast with the large variety of potentiometric and amperometric chemical sensors and optical sensors described in the literature [236], Similarly, the detection of ammonia in air has merited diflierent approaches in the field of chemical sensors. Screen-printed electrodes modified with Meldola s Blue and covered with a polycarbonate membrane constitute the basis of the catalytic detection of NHj. The measurement is based on the electrocatalytic reduction of NADH upon addition of glutamate dehydrogenase to a stirred solution containing NADH, 2-oxoglutarate and ammonium ions. The rate of current decrease (nA s ), measured at 50 mV, correlates to the concentration of ammonium ions in the sample. Recoveries of ammonium ions in spiked pond and tap waters at the level of 0.1 ppm are close to 100%, which demonstrates the feasibility of this assay for the detection of ammonium ions in waters [237],... 

Substitution of other oxoreductase enzymes for glucose oxidase allows amperometric biosensors for other substrates of clinical interest to be constructed. Practical sensors with commercial application in critical care analyzers for blood lactate have been realized. Other amperometric biosensors reported include cholesterol, pyruvate, alanine, glutamate, and glutamine. By using the multiple enzyme cascade shown in the reactions below, an amperometric biosensor for creatinine is also possible. Electrochemical oxidation of H2O2 is the detection mechanism. 

An amperometric sensor for amino acids based on flow injection analysis (FIA) and using microelectrodes (10 pm diameter) primarily of P(Py) doped with sulfonate dopants such as tosylate and 3-sulfobenzoate was demonstrated by Akhtar et al. [823, 824]. Linear response was demonstrated for analytes such as aspartic acid and glutamic acid over the concentration range 7.5 X 10 to lO" with sensitivities in the region of 1.5 nC-M and detection limits of ca. 10 M. These authors also showed the use of a pattern recognition technique using the responses of six detector electrodes. Fig. 17-11 shows typical response of one of their sensors. 

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