Separation of synthetic food colourants in the mixed micellar system. Application to pharmaceutical analysis

The paper presents a rapid method for the determination of commonly used synthetic food dyes by micellar electrokinetic capillary chromatography. Detection and separation conditions allowing complete resolution of 15 synthetic food colourants were investigated. The effect of different surfactants on the analytes mobility in relation to their structure was tested. After optimization procedure a dual micellar system was selected. All food dyes were separated in less then 20 min using a fused silica capillary in the borate/dodecylsulfate/deoxycholate buffer containing acetonitrile as organic modifier. The detection wavelength was set at 210nm. The method was successfully validated by determination of linearity ranges, detection limits, precision and repeatability for all colourants tested. In order to apply the method for pharmaceutical analysis a sample pretreatment procedures were found. Liquid pharmaceuticals were used as it or just after dilution with water. From tablets or capsules the colourants were isolated by adsorption on acidic aluminium oxide. The method was used for identification and if possible for quantification the synthetic food dyes in pharmaceuticals. The analytes are detectable at a concentration level 0.3-0.8 microg ml(-1).     

Capillary Condensation in Pores with Energetically Heterogeneous Walls: Density Functional versus Monte Carlo Calculations

We investigate adsorption of a Lennard-Jones fluid in slit-like pores with energetically heterogeneous walls by using Grand Canonical Monte Carlo simulations and a density functional approach. The model of a fluid-wall potential is qualitatively similar to that invoked by R?cken et al. (J. Chem. Phys. 108, 8089, (1999); i.e., it consists of a homogeneous part that varies in the direction perpendicular to the wall and a periodic part, varying also in one direction parallel to the wall, but in contrast to the above mentioned work, both parts of the fluid-wall potential are modeled by Lennard-Jones (9, 3) type functions. The structure of the adsorbed film is characterized by local densities. We evaluate the phase diagrams for several systems characterized by different corrugation of the adsorbing potential and discuss the discrepancies between theoretical predictions and computer simulations. Copyright 2001 Academic Press.     

A double layer study of the (210) and (111) faces of gold in aqueous NaBF4 SOLUTIONS

Au(111) and Au(21O) faces of gold in aqueous NaBF₄ solutions have been investigated using cyclic voltammetry and admittance measurements. On Au(21O) no specific adsorption of $B{F}_4^{?}$ has been found. The results were first analysed accepting the Gouy-Chapman-Stern model for the double layer; like Ag(11O) and Ag(100) the inner layer capacity versus charge density curve has a broad maximum. For Au(111) it was not possible to draw clear conclusions and the variation of the inner layer capacity versus charge density seems to correspond to the accepted model only for the more negative densities of charge investigated.Models for the inner layer were discussed for the (210) face.     

Reaction of acylaminocyanoesters with 2,4-bis (4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide leading to substituted aminothiazoles. Crysta

2-Acylamino-2-cyanoacetic acid ethyl esters $\text{2a-c}$ react with 2,4-bis (4-methoxyphenyl)-1, 3, 2, 4-dithiadiphosphetane 2,4-disulfide $\text{1}$ in refluxing benzene with formation of 2-alkyl(aryl)-5-aminothiazole-4-carboxylic acid ethyl esters $\text{3a-c}$. Structure $\text{3}$ was established by spectroscopic means and an X ray crystallographic investigation of $\text{3a}$. X-Ray analysis revealed that the thiazole ring, exocyclic nitrogen and carbonyl group forming a hydrogen-bonded cycle are nearly coplanar. A resonance interaction is manifested by distinctly shortened /1.447 (3)/ C_(carbonyl)-C_(thiazole) distance.     

Adsorption of acetone on the mercury electrode from H2O+(CH3)2CO+HCl solutions

The adsorption of acetone on a mercury electrode from (CH₃)₂CO+H₂O+HCl solutions has been studied using a thermodynamically rigorous procedure. The chemical potential of the supporting electrolyte has been kept constant by using the concentrations corresponding to the constant e.m.f. of the cell with electrodes reversible to each of the ions in the solutions. It is suggested that the molecule is to some extent oriented with the hydrocarbon part towards mercury. The composition of the surface layer has been calculated.     

Determination of silver in copper ores by atomic-absorption spectrophotometry after extraction separation with triphenylphosphine

Summary A procedure is proposed for determination of small amounts of silver in copper ores and processed products. The samples are dissolved in a Teflon bomb in a mixture of hydrofluoric and nitric acids, then evaporated in the presence of nitric and boric acids. Silver is extracted from the sample solution with a solution of triphenylphosphine in methyl isobutyl ketone, then determined by atomic-absorption spectrophotometry. The method is precise and accurate. The relative standard deviation for a silver content of 10^–4% is about 4%.

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Zusammenfassung Ein Verfahren zur Bestimmung kleiner Mengen Silber in Kupfererzen und daraus hergestellten Produkten wurde vorgeschlagen. Die Proben werden in einer Teflonbombe in einem Gemisch aus Flußsäure und Salpetersäure gelöst und dann in Gegenwart von Salpetersäure und Borsäure eingeengt. Das Silber wird mit Triphenylphosphin, gelöst in Isobutylmethylketon, aus der Probelösung extrahiert und dann mit Hilfe der AAS bestimmt. Das Verfahren ist genau, die relative Standardabweichung beträgt bei einem Silbergehalt von 10^–4% ungefähr 4%.

     

Thermal stability study of the protease inhibitors

A thermal and kinetic analysis of two protease inhibitors: nelfinavir mesylate and atazanavir sulfate, were carried out to find their thermal stability. DSC curves of both drugs showed exothermic transition. This observed process resulted in two steps. Obtained apparent activation energy pointed at low stability of studied protease inhibitors in water solutions.     

Stability and nature of complexes of the type MCl+ in aqueous solution (M=Mn,Co, Ni,and Zn)

Equilibrium constants have been determined both potentiometrically and spectrophotometrically for reactions of the type M²⁺+Cl^??MCl⁺ using aqueous solutions of the corresponding metal perchlorates as the reaction media (M=Mn, Co, Ni, and Zn). The variation in the quotient of the activity coefficients of these reactions with increasing molality of the reaction medium has been found to be approximately the same for the CuCl⁺ (previously studied), MnCl⁺, and ZnCl⁺ complexes, while a different dependence is observed for the CoCl⁺ and NiCl⁺ complexes. The results are interpreted as indicating equilibrium coexistence of the [MCl(OH₂)₅]⁺ and {[M(OH₂)₆]Cl}⁺ species in the latter two cases. Approximate values of the corresponding equilibrium constants are estimated in addition to the derived overall thermodynamic stability constants of the MCl⁺ formal complexes. The latter are found to follow a partly inverted Irving-Williams series, the fact being accountable in terms of the ligand field stabilization energy.     

Structure and UV-Vis spectroscopy of nitrosylthiolatoferrate mononuclear complexes

Density functional calculations for the [(RS)_xFe(NO)_4−x]⁻ (R=CH₃) compounds are carried out using the DFT method with the B3LYP functional. The results can be verified by the experimental data only in the case of the [(RS)₂Fe(NO)₂]⁻ complex. The experimentally characterised molecular structure of [(RS)₂Fe(NO)₂]⁻ (where (RS)₂=(SCH₂CH₂NMeCH₂CH₂CH₂NMeCH₂CH₂S) is properly reproduced by the RB3LYP method. The discrepancy between the calculated spin densities with the integral spin observed experimentally is interpreted in terms of antiferromagnetic coupling between the Fe(III) centre and the NO⁻ ligands. The theoretical analysis gives a good account of some properties observed in these compounds. In particular, the electronic spectrum calculated by the TDDFT method for [(CH₃S)₂Fe(NO)₂]⁻ is similar in shape to the experimental one, although is hypsochromically shifted. The LLCT (S_π→π^*_NO), LMCT (S_π→d) or (π^*_NO→d+S_π→d) and MLCT (d→π^*_NO) transitions are mostly responsible for absorption of the [(RS)_xFe(NO)_4−x]⁻ complexes within UV-Vis. The chemical reactivity of [(RS)₂Fe(NO)₂]⁻ is interpreted basing on the calculated effect of a polar solvent on the ligand polarity and on the character of the HOMO and LUMO orbitals.     

Highly diastereoselective Henry reaction of nitro compounds with chiral derivatives of glyoxylic acid

N-Glyoxyloyl-(2R)-bornane-10,2-sultam and (1R)-8-phenylmenthyl glyoxylate react stereoselectively with simple nitro compounds giving diastereoisomeric nitroalcohols with high asymmetric induction. N-Glyoxyloyl-(2R)-bornane-10,2-sultam 1a is shown to be a highly efficient chiral inducer, superior to (1R)-8-phenylmenthyl glyoxylate 1b. In all cases, the absolute (2S) configuration at the center bearing the hydroxy group and the relative syn configuration for the major diastereoisomers were determined.