Indirect fluorometric determination of diclofenac sodium.

A simple and easy method of analysis for diclofenac sodium is reported. A spectrofluorometric method for the microdetermination of diclofenac sodium has been developed through its reaction with cerium(IV) in an acidic solution and measurement of the fluorescence of the Ce(III) ions produced. Under the optimum experimental conditions for the oxidation reaction, 1.0 M H2SO4 with 90 min of heating time (100 degrees C), the range of application is 124.3-600 ng mL(-1) and the limit of detection is 72.7 ng mL(-1). The proposed method was applied to the determination of diclofenac sodium in pharmaceutical tablets. The results of the analysis show a good agreement with those obtained by the official USP 27 HPLC method.     

Reagentless system for sulphite determination based on polyaniline

A new reagentless system for sulphite (or sulphur dioxide) determination is reported based on the use of an organic conducting polymer, polyaniline, and its absorbance variation at 550 nm, depending on the sulphite concentration. After chemical polymerisation of aniline a very thin film of polyaniline is obtained. Although the response is not fully reversible, each film can be used for at least 10 measurements for low analyte concentrations (up to 0.5 mg l⁻¹) and five measurements for higher sulphite concentrations. Moreover, the reproducibility, ease of preparation and low cost of the films, permit the use of a new disposable system for each measurement. When the change in absorbance at 550 nm was measured for 210 s (stabilisation time), the system showed a linear response, which ranged from 0.025 to 1.50 mg l⁻¹ of sulphite. A theory with regard to the reaction mechanism between the polyaniline films and sulphite is also proposed. The system was applied to sulphite determination in wine samples and the results were in agreement with those obtained by the Official Method of Analysis (iodometric titration).     

Initial evaluation of quantitative performance of chromatographic methods using replicates at multiple concentrations

The introduction of a novel analytical method must be supported by consistent information about its quantitative potentialities; this is critical for whoever considers its utilization for an specific application. Unfortunately, literature abounds in papers proposing excellent chromatographic methods of analysis that have been subjected to comparatively poor quantitative evaluation. The methodology proposed in the present work makes use of some of the performance characteristics whose measurement is recommended in validation protocols; pertinent to this stage of method development are the detection and quantitation limits, the linear range and the repeatability. All this information can be calculated from the results of a calibration with several replicates at each analyte level. Replicates enable the calculation of reproducibility at several analyte levels and the estimation of the linear range; more important, replicates are necessary to detect changes in peak area standard deviation with analyte amount. Regression of calibration data by means of unweighted least-squares (ULSR) can only be performed in those cases in which homoscedasticity has been previously verified; heteroscedastic calibration data demand regression by means of weighted least-squares (WLSR), since ULSR results in gross overestimation of prediction limits at low analyte concentration. The proposal is used for the preliminary quantitative evaluation of a method for the determination of nine biogenic amines by means of pre-column derivatization with dabsyl chloride and separation of derivatives by RPLC. Limits of detection are calculated by a regression approach and by the classical signal-to-noise ratio method (S/N approach). No significant difference was detected for the amines limits of detection estimated by WLSR and by the S/N approach; ULSR estimated limits of detection are between 7 and 78 times larger than those obtained by the other two methods, as a consequence of the heteroscedasticity of calibration data.     

Rigid Motions in the Presence of a Magnetic Field

It is shown that, in the standard framework of non-relativistic quantum mechanics, the presence of a magnetic field implies that there are no operators representing those translations or rotations that do not leave invariant the magnetic field, and the corresponding components of the linear or angular momentum are undefined. Pacs: 03.65.-w. 02.20.-a     

Fast and accurate algorithm for the simulation of NMR spectra of large spin systems

The computational cost for the simulation of NMR spectra grows exponentially with the number of nuclei. Today, the memory available to store the Hamiltonian limits the size of the system that can be studied. Modern computers enable to tackle systems containing up to 13 spins [1], which obviously does not allow to study most molecules of interest in research. This issue can be addressed by identifying groups of spins or fragments that are not or only weakly interacting together, i.e., that only share weakly coupled spin pairs. Such a fragmentation is only permitted in the weak coupling regime, i.e., when the coupling interaction is weak compared to the difference in chemical shift of the coupled spins. Here, we propose a procedure that removes weak coupling interactions in order to split the spin system efficiently and to correct a posteriori for the effect of the neglected couplings. This approach yields accurate spectra when the adequate interactions are removed, i.e., between spins only involved in weak coupling interactions, but fails otherwise. As a result, the computational time for the simulation of 1D spectra grows linearly with the size of the spin system.     

Miscibility in poly(L-lactide)- b -poly( $ \upvarepsilon$ -caprolactone) double crystalline diblock copolymers

Thermally stimulated depolarization currents, TSDC, wide-angle X-ray scattering, WAXS, differential scanning calorimetry, DSC, and polarized light optical microscopy, PLOM, have been used to examine poly(L-lactide)-b -poly( -caprolactone) diblock copolymers in a wide composition range. Both components are crystallizable and the miscibility in the amorphous phase has been determined from the behavior of the primary relaxations which are the dielectric manifestation of the glass transition, and also from the superstructural morphology revealed by PLOM and the compositional dependence of the melting points as determined by DSC. Distinct segmental mobilities in the amorphous phase which can be well resolved by TSDC are present; the mode of the slower component shifts to lower temperatures as the PCL content increases while the glass transition of neat PCL is present for all compositions. A relaxation times bimodal distribution is apparent for PCL-rich copolymers. The composition dependence of the multiple glass transitions detected in these weakly segregated copolymers are predicted by the self-concentration model for a miscible blend made of components with a large T_g contrast.     

Photovoltaic structures using AgSb(S x Se1−x )2 thin films as absorber

Photovoltaic structures were prepared using AgSb(S _x Se_1?x )₂ as absorber and CdS as window layer at various conditions via a hybrid technique of chemical bath deposition and thermal evaporation followed by heat treatments. Silver antimony sulfo selenide thin films [AgSb(S _x Se_1?x )₂] were prepared by heating multilayers of sequentially deposited Sb₂S₃/Ag dipped in Na₂SeSO₃ solution, glass/Sb₂S₃/Ag/Se. For this, Sb₂S₃ thin films were deposited from a chemical bath containing SbCl₃ and Na₂S₂O₃. Then, Ag thin films were thermally evaporated on glass/Sb₂S₃, followed by selenization by dipping in an acidic solution of Na₂SeSO₃. The duration of dipping was varied as 3, 4 and 5 h. Two different heat treatments, one at 350 °C for 20 min in vacuum followed by a post-heat treatment at 325 °C for 2 h in Ar, and the other at 350 °C for 1 h in Ar, were applied to the multilayers of different configurations. X-ray diffraction results showed the formation of AgSb(S _x Se_1?x )₂ thin films as the primary phase and AgSb(S,Se)₂ and Sb₂S₃ as secondary phases. Morphology and elemental detection were done by scanning electron microscopy and energy dispersive X-ray analysis. X-ray photoelectron spectroscopic studies showed the depthwise composition of the films. Optical properties were determined by UV–vis–IR transmittance and reflection spectral analysis. AgSb(S _x Se_1?x )₂ formed at different conditions was incorporated in PV structures glass/FTO/CdS/AgSb(S _x Se_1?x )₂/C/Ag. Chemically deposited post-annealed CdS thin films of various thicknesses were used as window layer. J–V characteristics of the cells were measured under dark and AM1.5 illumination. Analysis of the J–V characteristics resulted in the best solar cell parameters of V _oc = 520 mV, J _sc = 9.70 mA cm^?2, FF = 0.50 and η = 2.7 %.     

Lifetimes of charged and neutralD mesons

We have measured the lifetimes of hadronically produced charged and neutralD mesons using silicon microstrip detectors and an active silicon target in the NA32 spectrometer at the CERN SPS. We obtainτ _D± = (10.9± _1.5 ^1.9 )·10^?13s andτ _D ^(?)10 = (4.2±0.5)·10^?13s based on 59 and 90 fully reconstructed decays respectively, giving a ratioτ _D±/τ _D ^(?)10 of 2.6 ±0.5.     

Embedded eigenvalues of Sturm Liouville operators

In this work we study the behavior of embedded eigenvalues of Sturm-Liouville problems in the half axis under local perturbations. When the derivative of the spectral function is strictly positive, we prove that the embedded eigenvalues either disappear or remain fixed. In this case we show that local perturbations cannot add eigenvalues in the continuous spectrum. If the condition on the spectral function is removed then a local perturbation can add infinitely many eigenvalues.     

A nonlinear programming algorithm based on non-coercive penalty functions

 We consider first the differentiable nonlinear programming problem and study the asymptotic behavior of methods based on a family of penalty functions that approximate asymptotically the usual exact penalty function. We associate two parameters to these functions: one is used to control the slope and the other controls the deviation from the exact penalty. We propose a method that does not change the slope for feasible iterates and show that for problems satisfying the Mangasarian-Fromovitz constraint qualification all iterates will remain feasible after a finite number of iterations. The same results are obtained for non-smooth convex problems under a Slater qualification condition. Received: September 2000 / Accepted: June 2002 Published online: March 21, 2003 Research partially supported by CAPES, Brazil Research partially supported by CNPq, Brazil, and CONICIT, Venezuela. Mathematics Subject Classification (1991): 20E28, 20G40, 20C20