Determination of barbituric acid and 2-thiobarbituric acid with end-column electrochemical detection by capillary electrophoresis

Capillary electrophoresis (CE) with end-column electrochemical detection (EC) of barbituric acid (BA) and 2-thiobarbituric acid (TA) has been described. Under optimum condition, BA and TA were separated satisfactorily, and a response of high sensitivity and stability was obtained at a detection potential of 1.25 V versus Ag/AgCl. Optimized end-column detection provides detection limit as low as 0.5 and 0.1 μM for BA and TA, respectively. The calibration graph was linear over three orders of magnitude. The relative standard deviations (n=10) of peak currents and migration times obtained for both BA and TA were 3.4, 3.7, and 1.7, 1.2%, respectively. The proposed method has been applied to analyze water sample with satisfactory results.     

Prediction of programmed-temperature retention values of naphthas by artificial neural networks

It is proposed for the first time a method of prediction of the programmed-temperature retention times of components of naphthas in capillary gas chromatography using artificial neural networks. People are used to predict the programmed-temperature retention time using many formulas such as the integral formula, which requires that four parameters must be determined by calculation or experiments. However the results obtained by the formula are not so good to meet the demand of industry. In order to predict retention time accurately and conveniently, artificial neural networks using five-fold cross-validation and leave-20%-out methods have been applied. Only two parameters: density and isothermal retention index were used as input vectors. The average RMS error for predicted values of five different networks was 0.18, whereas the RMS error of predictions by the integral formula was 0.69. Obviously, the predictions by neural networks were much better than predictions by the formula, and neural networks need fewer parameters than the formula. So neural networks can successfully and conveniently solve the problem of predictions of programmed-temperature retention times, and provide useful data for analysis of naphthas in petrochemical industry.     

NH-S hydrogen bonding in zinc enzyme model complex with S2N2 binding set studied by normal coordinate analysis of vibrational spectra

In order to provide theoretical evidence for the existence and effect of NH-S hydrogen bonding in the zinc enzyme model complex [Zn(S-2-C6H4NHCOC6H5)2(1-MeIm)2] (1-MeIm = 1-methylimidazole) in addition to the spectroscopic and crystallographic investigations, normal coordinate analysis (NCA) was carried out using a modified Urey-Bradley force field. The vibrational frequencies of the complex with and without the NH-S hydrogen bonding as well as the corresponding internal coordinates were obtained. The good agreement found between the calculated and observed frequencies in the presence of the NH-S hydrogen bond, supports the reliability of the analysis. The stretching force constant of the NH-S hydrogen bond obtained from the calculation is 0.18 mdyne per A. The calculation shows that the N-H bond is weakened by formation of the NH-S hydrogen bond. The results are indicative of the existence of the NH-S hydrogen bond in the complex.     

Digital light-directed synthesis. A microarray platform that permits rapid reaction optimization on a combinatorial basis

Solution reactions using photogenerated reagents (Gao, X.; Yu, P.; LeProust, E.; Sonigo, L.; Pellois, J. P.; Zhang, H. J. Am. Chem. Soc. 1998, 120, 12698) are a potentially powerful means for combinatorial parallel synthesis of addressable molecular microarrays. In this report, we demonstrate that this chemistry permits combinatorial screening of reaction conditions on a microarray platform. Using this method of optimization and our reaction apparatus, efficient photogenerated acids and reaction conditions suitable for removal of the acid labile protection group on 5'-O of nucleotides are identified in a short period of time. The chemistry platform demonstrated opens new avenues for rapid, simultaneous investigation of multiple reactions using different reagents and reaction parameters directly on a solid support (e.g., a glass plate). The combinatorial screening method described may be extended to include general organic reactions employing photogenerated and conventional reagents as well as a microarray reaction device. This should be especially valuable for efficient synthesis of addressable organic compound libraries.     

Copper-catalyzed aminohalogenation using the 2-NsNCl(2)/2-NsNHNa combination as the nitrogen and halogen sources for the synthesis of anti-alkyl 3-chloro-2-(o-nitrobenzenesulfonamido)-3-arylpropionates

New regio- and stereoselective aminohalogenation of cinnamic esters has been developed using the combination of 2-NsNCl(2)/2-NsNHNa as the nitrogen and chlorine sources and copper(I) triflate as the catalyst. The new procedure provides an efficient synthesis of anti-alkyl 3-chloro-2-(o-nitrobenzenesulfonamido)-3-phenylpropionate derivatives. Nine examples are presented with good yields (62-82%) and stereoselectivity ((5:1)-(30:1)).     

Rational Functions with a General Distribution of Poles on the Real Line Orthogonal with Respect to Varying Exponential Weights: I

Orthogonal rational functions are characterized in terms of a family of matrix Riemann–Hilbert problems on ?, and a related family of energy minimisation problems is presented. Existence, uniqueness, and regularity properties of the equilibrium measures which solve the energy minimisation problems are established. These measures are used to derive a family of ‘model’ matrix Riemann–Hilbert problems which are amenable to asymptotic analysis via the Deift–Zhou non-linear steepest-descent method.     

Scaling law of anomalous Hall effect in Fe/Cu bilayers

The scaling of anomalous Hall resistivity on longitudinal resistivity has been intensively studied in different magnetic systems, including multilayer and granular films, to examine whether a skew scattering or a side jump mechanism dominates in the origin of anomalous Hall effect (AHE). The scaling law is based on the premise that both resistivities are a consequence of electron scattering by the imperfections in the materials. By studying the anomalous Hall effect in the simple Fe/Cu bilayers, it was demonstrated that the measured anomalous Hall effect should not follow the scaling laws derived from skew scattering or side jump mechanism due to the short-circuit and shunting effects of the non-magnetic layers.     

Capillary electrophoresis using diol-bonded fused-silica capillaries

In this paper, 3-glycidoxypropyltrimethoxysilane was used to produce diol-bonded capillaries at room temperature for capillary electrophoresis (CE). A variety of standard reference compounds and authentic biological samples including ribonucleotides, peptides and proteins were used to test the columns. It was found that greatly suppressed electroosmotic flow was measured over a pH range of 3–10. Lower than 1.6% relative standard deviation (>10 runs) in migration time was observed for the analysis of test proteins. For real samples of ribonucleotides in tumor cell extracts, 1 million theoretical plates and excellent peak shapes were obtained. The high column efficiency and symmetrical peaks allowed the separation of samples with only 0.6% maximum difference in migration times. The diol-bonded fused-silica capillary columns were stable when used in a pH range of 2–8 under typical CE conditions. The column preparation method involved a simple dynamic coating procedure at room temperature, greatly simplifying the more typical static coating methods that require vacuum pumps and ovens.     

In-situ external reflection FTIR spectroelectrochemical and XPS investigations of cobalt-cyanometallates as inorganic polymeric materials on a platinum electrode

This paper provides an introduction to the workshop on methodologies for wastewater quality monitoring, Nimes, 29-30 October 1998, organised by the European Commission and Ecoles des Mines d'Alès. It highlights some overall aspects for the potential uses of on-line instrumentation related to wastewater management and focuses on relations to the urban wastewater treatment directive (91/271/EEC). Some potentials for further developments and actions related to the EU Directive are proposed.     

Separation and determination of fluoride in plant samples

A simple and rapid separation method is described for the determination of fluoride in plant samples. Fluoride is separated by distillation in the presence of H(2)SO(4) and H(2)O(2) in a dry air steam. The variables that influence the distillation quantitation were optimized. The fluorides separated were subsequently determined by a spectrophotometric method of the La(III)-F(-)-alizarin complexone system. The precision of the procedure was significant, and the RSD was 3.7%. The accuracy of the method was statistically satisfactory, and the recovery was from 95.9 to 104.4%.