A study of changes in the yields of radiolytic products in two-phase systems with tributyl phosphate

With the aim of studying the effects of volume ratios and composition of the organic phase on the total yields of the main degradation products of tributyl phosphate (TBP) radiolysis, the following two-phase systems were used: water-TBP-carbon tetrachloride and water-TBP-n-alkane with various ratio of TBP in the organic phase and various volume ratios of organic-aqueous phases. We examined the influence of the distribution of two-phase systems components-precursors of radiolytic products on the total yields of the main radiolytic products and mechanism involved.     

The β-carotene dilemma: ESR study with coordinated peroxyl radicals

The apparently unpredictable behaviour of β-carotene in the supplementation of the diet of smokers is discussed in the light of the reactions of peroxyl radicals with β-carotene in the absence of oxygen. The decay of tert-butylperoxyl radicals in the presence of β-carotene was studied at ambient temperature in non-polar solvents by ESR spectroscopy. The primary reaction in the absence of oxygen is interpreted as a spin-trapping effect of a peroxyl radical by β-carotene producing an intermediate labile free radical, which disappears after recombination with a second tert-butylperoxyl radical. The result is the transformation of β-carotene to a diamagnetic compound with two peroxy bonds. In the presence of chelating transition metals with unpaired d-electrons as electron donors the peroxy group of the oxidized β-carotene can be split to alkoxyl free radicals. The primary attack of tert-butylperoxyl radicals is completely inhibited in the presence of vitamin E followed by production of free aryloxy radicals and the presence of oxygen has no significant effect on this reaction. Spin-trapping of peroxyl radicals by the double bond of vitamin A leads to its oxidation in the absence of vitamin E. Transition metal ions such as Co, Cr, Fe, and Mn, known to be present in the aerosol of cigarette smoke, homolyse the peroxyl bonds of peroxidised β-carotene, which results in cell damage.     

Determination of the enantiomeric composition of chiral carboxylic acids using chiral derivatization and HPLC

Summary The enantiomers of chiral carboxylic acids were separated as their diastereomeric amides with (1R,2R)-(−)-1-(4-nitrophenyl)-2-amino-1,3-propanediol (“levobase”) and with “dextrobase” (the enantiomer of levobase) by high-performance liquid chromatography using a conventional C-18 column and various solvent systems containing acetonitrile, methanol, water, and phosphoric acid.     

Comparative study on separation of diastereomers by HPLC

Summary Reversed (RP-HPLC) and normal phase chromatographic (NP-HPLC) separations have been developed for diastereomers ofN-acyl-1-methyl-1,2,3,4-tetrahydo-β-carbolines which are acylated derivatives of simple natural β-carboline alkaloids. Separations of derivatives having different acyl moieties in theO,O-diacyl-tartaric acid ester subtituent differed remarkably. Little or no resolution in either NP-HPLC or RP-HPLC could be achieved with the diacetyl-tartrate derivative. Base-line separation by RP-HPLC but no separation by NP-HPLC was possible with the bulkier and more apolar dipivaloyl derivative. Retention order of the bis-benzoylated diastereomers was reversed and separation time increased dramatically by RP-HPLC. Good separation of the medium polarity, but rigid,N-camphanyl derivative by NP-HPLC has been achieved, whereas RP-HPLC could not be used for separation of these diastereomers. Separability of different diastereomers was highly dependent on polarity and rigidity of the derivatizingN-acyl moieties. Conformational analysis by molecular mechanics and comparison of the lowest energy conformational states of the diastereomers was applied to rationalise separation-retention behaviour of stereoisomers by RP-HPLC. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001     

Analysis of cyanobacterial toxins (anatoxin-a, cylindrospermopsin, microcystin-LR) by capillary electrophoresis

Capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) were applied to the simultaneous separation of cyanobacterial toxins (anatoxin-a, microcystin-LR, cylindrospermopsin). The analytical performance data of both methods, optimized for the three toxins, were similar with a precision of migration times smaller than 0.8 RSD% and a detection limit in the range of 1-4 microg/mL, using spectrophotometric detection at 230 nm. Both methods were applied to an analysis of cyanotoxins in water bloom samples and crude cyanobacterial extracts. The results obtained indicate that, for complex matrices, the sequential application of CZE and MEKC is necessary. It is recommended to use both CE techniques for the analysis of the same sample in order to confirm the results by an orthogonal approach.     

Development of a chromatographic method for the determination of saquinavir in plasma samples of HIV patients

A simple, sensitive and reproducible high-performance liquid chromatographic method for detecting and quantifying saquinavir in human plasma is described. Verapamil was used as internal standard. The method employes a single liquid-liquid extraction step with tert-butil methyl ether followed by chromatography on a Lichrospher 60 Select B C8 reversed-phase column. Ultraviolet detection was used to identify the compounds of interest. The quantitation limit of saquinavir was 1 ng/mL and only 0.5 mL of plasma sample was required for the determination. The average saquinavir recoveries over a concentration range of 2.5-500 ng/mL ranged from 86 to 95%. Precision and accuracy did not exceed 5%.     

Selenium speciation by coupling vesicle mediated HPLC with off-line ETAAS and on-line focused microwave digestion HG-AAS detection

A novel High Performance Liquid Chromatography (HPLC) method for the separation of selenium species with specific detection by off-line Electrothermal Atomization Atomic Absorption Spectrometry (ETAAS) or on-line focused microwave digestion (MW) Hydride Generation Atomic Absorption Spectrometry (HG-AAS) is described. Vesicular mobile phases of the cationic surfactant didodecyldimethylammonium bromide (DDAB) have been evaluated for the liquid chromatographic separation of inorganic selenium (selenite and selenate) and different selenoaminoacids (selenocystine, selenomethionine and selenoethionine) on a C(18) reversed-phase column modified by DDAB molecules. The effects of different parameters (pH, buffer and vesicle concentrations) of the mobile phase on the retention times have been determined. The detection limit for selenium with the proposed off-line HPLC-ETAAS method has been found to be 5 microg/L of Se. The detection limit using HPLC-"on line" focused microwave digestion-HG-AAS has been found to be 1 microg/L of Se, with a precision (repeatability) better than +/- 5%. The latter proved to be an exceptional on-line real-time chromatographic detector for selenium speciation purposes.     

Preparation and characterization of Mg(II)-, Ca(II) and Cd(II) complexes of 1,2-ethanediol and water

Mixed ligand complexes of different compositions were prepared with water, sulfate ion and 1,2-ethanediol as ligand. IR spectra and the thermoanalytical curves of the complexes were recorded. Oxygen atoms bound by one or two coordinate bonds to the metal ion, or by hydrogen-bonds in the crystal, were observed. As for the water molecule, 1,2-ethanediol molecules of crystal and monohydrate type were found, depending on the type of binding of the oxygen atoms.This revised version was published online in November 2005 with corrections to the Cover Date.     

A note on the radical of a Banach algebra

Relying on the results of the paper [5], we show that the Jacobson radical of a Banach algebra can be characterized as the set of exactly those elements perturbations by which leave the spectrum invariant. A number of corollaries are listed.