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排序方式: 共有89条查询结果,搜索用时 15 毫秒
1.
Ovshinsky SR Young RT Allred DD DeMaggio G Van der Leeden GA 《Physical review letters》1987,58(24):2579-2581
2.
The construction and properties of a new urea-sensing membrane electrode capable of making direct urea measurements in whole blood are described. The electrode has a layered structure in which a small quantity of EDTA-stabilized urease enzyme solution is held between an external dialysis membrane and the gas-permeable membrane of a conventional ammonia selective electrode. It is shown that the electrode functions reliably in whole blood samples, used with minimal pretreatment, as well as in serum or aqueous solutions. The range, dynamic response, lifetime, precision, and accuracy of the electrode system are appropriate for clinical measurements in whole blood or serum, and promise to simplify such analyses with an attendant reduction in costs. 相似文献
3.
The coenzyme pyridoxal-5'-phosphate (PLP) is deiermined by in situ measurement of the rate of ammonia production using a potentiometric gas-sensing membrane electrode. It is shown that the initial rate of ammonia liberation from L-tryptophan by action of tryptophanase apoenzyme and the coenzyme can be linearly related to PLP levels in the nanogram range with minimal interference from related compounds. Calibration data for the 1 × 10-7–2.5 × 10-6 M range for PLP yielded a least-squares equation of rate (mV min-1) = (0.64 ± 0.01) C — 0.01 ± 0.02 with a standard error of 0.02 mV min-1, where concentration, C, is expressed in units of 10-7 mol l-1. 相似文献
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Results are presented for potentiometric ammonia gas-sensors which show that the response times increase significantly with age of the sensor when ammonium picrate is used as internal electrolyte and the samples have greater osmolarities than the internal electrolyte solution. A build-up of ammonium picrate crystals on the inner side of the gas-permeable membrane is responsible for this increasein response time. The use of ammonium chloride as internal electrolyte provides constant response times indepent of sample osmotic strength, and is recommended as a means of ensuring that optimal dynamic response characteristics are maintained. 相似文献
7.
Summary The response of glass electrodes to rapid changes in ion concentrations is considered from a theoretieal viewpoint. An expression is derived which describes the potential vs. time behavior of glass eleotrodes in terms of a new constant which may be useful in the characterization and selection of glass compositions. Agreement between glass electrode response predicted by the theory and available experimental data is excellent.
The financial support of NIH Grant GM-10086-03 and NSF Grant GP-1093 is gratefully acknowledged.
Alfred P. Sloan Research Fellow. 相似文献
Zusammenfassung Die Ansprechbarkeit von Glaselektroden auf rasche Änderungen der Ionenkonzentration wird vom theoretischen Standpunkt aus erörtert. Eine Gleichung wird abgeleitet, die das Elektrodenpotential als Funktion der Zeit erfaßt und eine neue Konstante enthält, die zur Beurteilung und zur Auswahl der Zusammensetzung von Gläsern dienen kann. Es besteht eine sehr gute Übereinstimmung zwischen theoretisch vorausgesagter und experimentell geprüfter Ansprechbarkeit von Glaselektroden.
The financial support of NIH Grant GM-10086-03 and NSF Grant GP-1093 is gratefully acknowledged.
Alfred P. Sloan Research Fellow. 相似文献
8.
A novel potentiometric membrane electrode with selective response to L-glutamate over the 2 × 10-4–1.3 × 10-2 M concentration range is constructed by immobilizing slices of yellow squash tissue at a CO2 gas sensor. This system represents the first successful use of intact plant materials as biocatalysts in the construction of bioselective potentiometric membrane electrodes; as a result, the range of future possibilities may be greatly extended. The glutamate-sensing electrode combines excellent selectivity characteristics over some 25 possible interferences tested, good reproducibility, and a useful lifetime of 7 days in aqueous samples. 相似文献
9.
A spectrophotometric study of silver(II) in sulphuric acid solution indicates the formation of two sulphate complexes, in the range 4–18M H2SO4, with absorbance peak maxima at 361 and 260 mμ, respectively. In 15M H2SO4 the molar absorptivity of silver(II) is 3.11 × 104 at 361 mμ. Kinetic studies of the reduction of silver(II) by the solvent suggest a rate-determining step first order in silver(II) and yield a pseudo first-order rate constant of 1.9 × 10−1min−1. Further studies as a function of H2SO4 concentration show that the specific decomposition rate of the two complexes is identical and that changes in H2SO4 concentration only serve to shift the concentration equilibrium between the two complexes. 相似文献
10.
A highly selective enzyme electrode for creatinine, based on tripolyphosphate-activated creatininase enzyme, is described and evaluated. Kinetic studies comparing purified creatininase enzyme in the activated and non-activated forms show that the activation mechanism involves an increase in Vmax but no change in Km. The analytical effect of enzyme activation is to extend the sensitivity of the electrode to lower limits and to improve the response slope of calibration curves. As a result, this activated creatininase enzyme electrode shows promise as a sensor for urine and serum samples. 相似文献