Simultaneous determination of dapsone and pyrimethamine by derivative spectrophotometry in pharmaceutical formulations

A simple and fast method was developed for the simultaneous determination of dapsone and pyrimethamine by first-order digital derivative spectrophotometry. Acetonitrile was used as a solvent to extract the drugs from the pharmaceutical formulations, and the samples were subsequently evaluated directly by digital derivative spectrophotometry. The simultaneous determination of both drugs was performed by the zero-crossing method at 249.4 and 231.4 nm for dapsone and pyrimethamine, respectively. The best signal-to-noise ratio was obtained when the first derivative of the spectrum was used. The linear range of determination for the drugs was from 6.6 x 10(-7) to 2.0 x 10(-4) and from 2.5 x 10(-6) to 2.0 x 10(-4) mol/L for dapsone and pyrimethamine, respectively. The excipients of commercial pharmaceutical formulations did not interfere in the analysis. Chemical and spectral variables were optimized for determination of both analytes. A good level of repeatability, 0.6 and 1.7% for dapsone and pyrimethamine, respectively, was observed. The proposed method was applied for the simultaneous determination of both drugs in pharmaceutical formulations.     

Capillary gas chromatography of n-butyl and isobutyl-, n-amyl and isoamyl polyethylene glycol ethers and their derivatives

The influence of a branching and increase in the length of alkyl and polyoxyethylene chain in homologous series of n-butyl and isobutyl-, n-amyl and isoamylpolyethylene glycol ethers on the retention indices at linearly programmed temperatures of a capillary column was studied. Alkylpolyethylene glycol ethers were converted by derivatization reactions into acetates, trifluoroacetates, and trimethylsilyl ethers. The influence of the structure of the alkylpolyethylene glycol molecule and the influence of the functional groups introduced into a molecule of studied compounds were examined by means of increments of retention index. Calculated retention indices were used to identify residues of individual oligomers in the products of biodegradation.     

An X-ray study of some 2,3-diphenyltetrazolium salts

An X-ray diffraction study is reported for three molecules of salts containing a cation with a positive charged 2,3-diphenyltetrazolium ring. The results confirm aromatic structure of the tetrazole ring and the delocalization of charge on the whole molecules of the cations. The molecular geometry obtained is compared with that for free mesoionic 2,3-diphenyltetrazoles which have already been studied and the ring parameters do not reveal significant differences. But is shows that the geometry of the (NNO)^– exocyclic group is changed as a result of alkylation. Compound I C₁₃H₁₂N₅Cl, P2₁/a,a=16.934(4),b=6.575(1),c=26.121(4) Å, =108.15(2)°, II C₁₄H₁₃N₆OI, P3₁2,a=10.774(3),c=12.821(4) Å, IV C₂₆H₂₀N₈Cl₂, C2/c,a=22.316(4),b=6.6903(7),c=20.437(3) Å, =92.51(1)°.     

Stranski-Krastanov formation of InAs quantum dots monitored during growth by reflectance anisotropy spectroscopy and spectroscopic ellipsometry

In this study the successful application of reflectance anisotropy spectroscopy (RAS) and spectroscopic ellipsometry (SE) for the in-situ investigation of InAs quantum dot growth on GaAs (001) in Stranski-Krastanov growth mode is reported. Both techniques provide the precise determination of the growth mode transition from two-dimensional InAs layer to three-dimensional island growth. In order to optimize the growth conditions, spectral and time-resolved measurements were performed for different growth parameters (temperatures, growth rates and V/III ratios). For high temperature deposition large additional anisotropies, caused by clusters elongated in the [110] direction were found. Decreasing the deposition rate (0.5 to 0.125 ML/s) also results in the formation of large clusters, as decreases in reflectivity due to larger stray light losses prove. Finally, increasing the AsH₃ partial pressure leads to an earlier onset of island formation and an enhanced tendency for cluster formation.     

Growth monitoring by reflectance anisotropy spectroscopy in MOVPE reactors for device fabrication

Reflectance anisotropy spectroscopy (RAS) has proved its capability to study surface processes during metalorganic vapour phase epitaxy (MOVPE) growth of a variety of III–V compounds. However, these investigations up to now have been mostly restricted to specialized research reactors. Therefore, we studied the feasibility of in-situ monitoring by RAS during growth on two production-type MOVPE reactors: horizontal 2 inch single wafer reactor AIX 200 and Planetary Reactor™ AIX 2000 for 5 × 3 inch. The slight modifications of the reactors necessary to gain normal incidence optical access to the sample do not alter the properties of the grown materials. While in the horizontal reactor the strain-free optical window allows one to obtain well-resolved RAS spectra the signals in the multiwafer reactor are affected by the anisotropy of the ceiling plate. Even in this case RAS spectra can be extracted. First measurements on rotating samples in the horizontal reactor demonstrate the possibility to obtain RAS spectra by multitransient spectroscopy. As an application monitoring of the growth of p-type layers for the base of GaInP/GaAs hetero-bipolar-transistors (HBTs) is discussed. The linear electro-optic effect (LEO) gives information on doping type and doping level. Time-resolved transients at specific energies are used to study the impact of different switching schemes on the properties of the base-emitter interface.     

Variable selection in discriminant analysis based on the location model for mixed variables

Non-parametric smoothing of the location model is a potential basis for discriminating between groups of objects using mixtures of continuous and categorical variables simultaneously. However, it may lead to unreliable estimates of parameters when too many variables are involved. This paper proposes a method for performing variable selection on the basis of distance between groups as measured by smoothed Kullback–Leibler divergence. Searching strategies using forward, backward and stepwise selections are outlined, and corresponding stopping rules derived from asymptotic distributional results are proposed. Results from a Monte Carlo study demonstrate the feasibility of the method. Examples on real data show that the method is generally competitive with, and sometimes is better than, other existing classification methods.     

Eine graphische Lösung des Wasserschloßproblems mit nomographischen Hilfsmitteln

Ohne Zusammenfassung     

Synthesis of new 1,2,4-triazolines and 1,3,4-thiadiazolines from bithioureas

2,4-Disubstituted thiosemicarbazides 1 react with acyl isothiocyanates to give bithioureas 2 , which by the action of sodium ethanolate cyclize to 1,2,4-triazoline-3-thiones 3 and 5 , respectively. Treatment of 2 with methyl iodide yields 1,3,4-thiadiazoline-2-imines 8 isomeric with 3 . Compound 8d undergoes a thermal induced DIMROTH rearrangement to give 3d in good yield.