Enzymatic methods for the determination of alpha-glycerophosphate and alpha-glycerophosphate oxidase with an automated FIA system

A procedure for the enzymatic determination of alpha-glycerophosphate (alpha-GP) has been developed, using an automated in-house FIA system, with immobilized glycerol-3-phosphate oxidase (GPO) on non-porous glass beads, following optimization of the immobilization and analytical parameters. Fabricated single bead string reactors (SBSR) were used in connection with the FIA system, following optimization of its parameters. The half-life of GPO-SBSR regarding reduction of the enzyme activity was found to be 110 days for its use in 20 triplicate measurements daily and storage at 4 degrees C in the appropriate buffer. The regression equation of the calibration graph for the determination of alpha-GP was: A(max)=(10+/-2)x10(-4)+(22 134+/-12)x10(-4) (mmol l(-1)alpha-GP). The lower limit of quantitation was 0.74 mumol l(-1)alpha-GP and the RSD of the method 0.05% (r=0.9999). The same FIA system and procedure can be also used for the determination of the GPO activity, with the alpha-GP as substrate. The regression equation for this calibration graph was: A(max)=(23+/-18)x10(-4)+(190+/-1)x10(-4) (mug ml(-1) GPO), the lower limit of quantitation was 0.782x10(-3) mg ml(-1) (0.782 ppm) GPO and the RSD of the method 0.53% (r=0.9999). Serum samples obtained from hospitalized patients were deproteinized by gel filtration and analyzed under pseudo-first order conditions, at various concentrations of alpha-GP. A kinetic study of the reduction of alpha-GP in serum versus time is given and an observed reaction rate constant k(ob)=106.5x10(-4) min(-1) was determined.     

Immobilization of glutamate dehydrogenase on glass derivatives. A method for the assay of glutamates in real samples with simplex optimized automated FIA-system

An enzymatic method for the determination of glutamic acid in food samples and pharmaceuticals is described. l-Glutamate dehydrogenase (GLDH) from beef liver was immobilized on isothiocyanate modified Controlled Pore Glass for the construction of a packed bed reactor. The NADH produced from the enzymic reaction was monitored fluorimetrically. The working curve is linear up to 200 mumol/l glutamate for an injection volume of 58 mul. The detection limit of the method is 0.3 mumol/l. The composite modified simplex was employed for the selection of the proper experimental conditions using an in-house flow injection manifold. Many interfering species and several amino acids were tested to verify the specificity of the enzyme reactor. The system works selectively for glutamic acid. The method is ideally suited to the assay of glutamic acid in a large number of samples because of its simplicity, stability and low cost. Forty-five samples per hour can be analyzed with a relative standard deviation better than 2%. The reactor is stable for a period of more than four months under specified storage conditions. The accuracy of the proposed method is tested by comparison of the results with those obtained by the official methods and the manufacturer's specifications for the analyzed samples. Good correlation was attained. Recovery experiments showed results between 97 and 104%.     

Determination of ionic and organically bound zinc in the sperm of the sea urchin by atomic absorption spectrophotometry

A method of extraction and assay of Zn in the sperm of sea urchin is developed. Three different extraction reagents are used in order to differentiate the fractions of the differently bound Zn in the sperm. The determination of concentration of Zn was made by atomic absorption spectrophotometry after constructing working curves with standard solutions of Zn.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

Kinetic study of the reaction between Fe2+-oxalate and 2,6-dichlorophenolindophenol

Ascorbic acid present in natural products is often analyzed by its reducing effect on 2,6-dichlorophenolindophenol (DCPI). In case of coexistence of Fe(II) in natural samples and if oxalic acid is used for their extraction and stabilization, a significant interference is observed. The reaction of Fe²⁺ with 2,6-dichlorophenolindophenol (DCPI) in acidic solutions in the presence or absence of oxalate ions was investigated. The reaction was studied with a Stopped-Flow Spectrophotometer (S.F.S) equiped with a data acquisition system, which allows the determination of initial rates and reaction rate constants. Results for the effect of the concentrations of all the reagents of the reaction are presented. During the experimental work all concentrations of the reagents were kept in such levels to make the reaction first-order in respect of DCPI. An interesting finding is, that, although Fe²⁺ and C₂O₄²⁻ ions do not react separately with DCPI (or react very slowly), they react very rapidly in mixtures and show a strong synergetic effect. The experimental data fit with the mechanism of the formation of intermediates FeC₂O₄ and [Fe(C₂O₄)₂]²⁻. The proposed rate law agrees with the above mechanism and the experimental results. The value k_c=(1.6±0.2)×10⁵ M⁻¹·s⁻¹ was calculated for the second-order rate constant of the reaction of FeC₂O₄ and DCPI. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 941–948, 1998     

Quantum Zeno and anti-Zeno paradoxes

Continuous observation of a time independent projection operator is known to prevent change of state (the quantum Zeno paradox). We discuss the recent result that generic continuous measurement of time dependent projection operators will in fact ensure change of state: an anti-Zeno paradox.     

粉粒体两相流的电容层析成象测量

粉粒体系统中的固相浓度分布的在线测量是十分困难的问题．电容层析成象技术是一种近年来发展起来的非侵入式快速浓度场测量技术．它不干扰流场，不受流动中颗粒浓度、加速度、不透明等因素的制约．本文讨论其测量原理、应用、近期进展、存在的主要问题及其解决的对策．