Investigation of in-line solid-phase extraction capillary electrophoresis for the analysis of drugs of abuse and their metabolites in water samples

In this study, in‐line solid‐phase extraction (SPE) was used as an enrichment technique in combination with CE for the preconcentration and separation of 2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine (EDDP), cocaine (COC), codeine (COD) and 6‐acetylmorphine (6AM). The separation buffer (BGE) used was 80 mM disodium phosphate anhydrous and 6 mM of HCl (final BGE pH of 3). The SPE extractor consists of a small segment of capillary filled with Oasis HLB sorbent and inserted into the inlet section of the electrophoretic capillary. Different parameters affecting preconcentration were evaluated, such as sample pH, the volume of the elution plug and sample injection time. The detection limits (LODs) reached for standard samples by in‐line SPE‐CE‐UV ranged between 50 and 200 ng/L, with sensitivity enhancement factors ranging from 2300 to 5300. Reproducibility values (expressed in terms of relative standard deviation) were below 7.6% for standard samples. This is a simple and an effective method for the determination of the studied drugs of abuse and their metabolites. The applicability of the developed method was demonstrated in tap and river water samples which were directly analyzed without any off‐line pretreatment. Analytical parameters were evaluated and LODs were between 70 and 270 ng/L with relative recoveries between 85 and 97%.     

Imbedding potentials in tent spaces

We obtain characterizations of positive Borel measures μ on so that the nonisotropic potential space K_α[L^p(dσ)] is imbedded in the tent space T₂^q(dμ), where 1<p,q<+∞. We deduce characterizations for pointwise multipliers of the space H_α^p.     

Electronic state of the molecular oxygen released by catalase

In catalases, the high redox intermediate known as compound I (Cpd I) is reduced back to the resting state by means of hydrogen peroxide in a 2-electron reaction [Cpd I (Por(*+)-Fe(IV)O) + H(2)O(2) --> Enz (Por-Fe(III)) + H(2)O + O(2)]. It has been proposed that this reaction takes place via proton transfer toward the distal His and hydride transfer toward the oxoferryl oxygen (H(+)/H(-) scheme) and some authors have related it to singlet oxygen generation. Here, we consider the possible reaction schemes and qualitatively analyze the electronic state of the species involved to show that the commonly used association of the H(+)/H(-) scheme with singlet oxygen production is not justified. The analysis is complemented with density functional theory (DFT) calculations for a gas-phase active site model of the reactants and products.     

Application of polydimethylsiloxane rod extraction to the determination of sixteen halogenated flame retardants in water samples

An extraction and preconcentration procedure for the determination in water samples of several halogenated flame retardants (FRs), nine brominated diphenyls ethers (BDEs) and seven non-BDE FRs, was developed and validated. The optimised procedure is based on polydimethylsiloxane (PDMS) rods as sorptive extraction material, followed by liquid desorption and gas chromatography coupled to negative chemical ionisation–mass spectrometry (GC–NCI–MS) determination, rendering an efficient and inexpensive method. The final optimised protocol consists of overnight extraction of 100 mL of sample solutions containing 40% MeOH and 4% NaCl, followed by a 15-min sonication-assisted desorption with 300 μL of ethyl acetate, solvent evaporation and GC–NCI–MS analysis. Under these conditions, extraction efficiencies in the 9 to 70% range were obtained, leading to enrichment factors between 108 and 840, detection limits in the range from 0.4 to 10 ng L⁻¹and RSD values in the 2–23% range. After method validation, different real water samples, including river, ria, sea, landfill leachate, influent and effluent wastewater from an urban sewage treatment plant (STP) and effluent wastewater from a textile industry, were analysed. BDE-47, BDE-99, BDE-100 and BDE-197 were detected in wastewater and landfill leachate samples at concentration levels up to 2887 ng L⁻¹. Among the non-BDE FRs, bis (2-ethylhexyl)-3,4,5,6-tetrabromo-phthalate (DEHTBP) was detected in surface water samples (sea, river and ria) between 1.3 and 2.2 ng L⁻¹ and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) in the landfill leachate (64 ng L⁻¹).     

Smectic A liquid crystal configurations with interface defects

We study planar energy minimizing configurations of smectic A liquid crystal materials and classify the corresponding defect structures. We investigate focal conic configurations in wedge, non‐parallel plates, funnel‐shaped domains, and non‐concentric annuli. The application of the stability condition for focal conics is relevant to the specification of the location of the interfacial defects. Self‐similar structures are discussed for a class of solutions with the same bulk energy. We propose surface energies terms to serve as selection mechanisms of particular self‐similar configurations. We also show how the modelling of chevron texture naturally arises in the present framework. Copyright © 2001 John Wiley & Sons, Ltd.     

Determination of enantiomeric purity of a novel COX-2 anti-inflammatory drug by capillary electrophoresis using single and dual cyclodextrin systems

E-6087 is the most advanced compound among the cyclooxygenase-2 (COX-2) inhibitor drugs developed in our company. Its activity is mainly associated with the S(-)-enantiomer (E-6232), whereas the R(-)-enantiomer (E-6231) becomes an impurity whose content should be determined. Five main impurities and degradation products of E-6232 have been found (E-6144, E-6024, E-6072, E-6397 and E-6132), and some of them co-elute with the distomer when using a chiral high-performance liquid chromatography (HPLC) method. Consequently, we have optimized the separation of all the impurities from the two enantiomers of E-6087 by capillary electrophoresis (CE), in order to use the method for the enantiomeric purity determination of E-6232. The effect of the methanol (MeOH) content in the background electrolyte (BGE), the sulfobutyl ether-beta-cyclodextrin (SBE-beta-CD) and heptakis-(2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CD) concentration, and the capillary temperature have been studied. Separation of all compounds could be achieved in different systems, either in a single CD-system (with SBE-beta-CD) or in a dual CD-system (with DM-beta-CD as a neutral CD). By using the dual CD system a limit of detection (LOD) and a limit of quantitation (LOQ) of 0.03% and 0.1% of distomer, respectively, were achieved*.     

Structure-energy relations in methylcobalamin with and without bound axial base

The properties of the Co-C bond in methylcobalamin (MeCbl) are analyzed by means of first-principles molecular dynamics. The optimized structure is in very good agreement with experiments, reproducing the bent-up deformation of the corrin ring as well as the metal-ligand bond distances. The analysis of the binding energies, bond orders, and vibrational stretching frequencies shows that the axial base slightly weakens the Co-C bond (by 4%), while the alkyl ligand substantially reinforces the Co-axial base bond (by 90%). These findings support several experiments and provide insight into the conversion between the base-on and base-off forms of the MeCbl cofactor.