Low-temperature clean-up method for the determination of pyrethroids in milk using gas chromatography with electron capture detection

This paper describes a new gas-chrormatography with electron capture detection (GC-ECD) method for determination of some pyrethroids in milk samples. The extraction of the pyrethroids was carried out by liquid–liquid extraction with clean-up by precipitation at low temperature, without additional stages for removal of fat interferences. The method was efficient with recoveries of 93.0 ± 0.1% for cipermethrin and 84.0 ± 0.3% for deltamethrin. The quantification limits were 0.75 μg L⁻¹ for both pyrethroids. The method was simple, of easy execution, and used only small quantities of organic solvent. After optimization and validation, the method was used for the determination of residues of the pyrethroids cipermethrin and deltamethrin in milk and in lactea drink commercialized in Viçosa (MG, Brazil). Some samples presented contamination with deltamethrin at levels below the maximum contamination limits established by the FAO.     

Thiacarbocyanine as ligand in dye-affinity chromatography for protein purification

A thiacarbocyanine has been post-grafted onto beaded cellulose by a curing method envisioning their use as a biomimetic ligand in dye-affinity chromatography. The immobilization of this dye was performed based on a previously brief derivatization study where the analogous microcrystalline cellulose was alternatively used and some of the curing reaction conditions were varied. The grafted beaded cellulose so obtained was qualitatively and quantitatively characterized by SEM, SEM-EDS and EA. The immobilized dye-affinity interaction with the standard proteins bovine serum albumin, alpha-chymotrypsin and lysosyme was analysed. The influence of the mobile phase composition on the chromatographic behaviour of these standard proteins was also studied. A selective interaction was observed allowing the separation of all the three proteins from an artificial mixture.     

Simulated effects of transient nucleation on the crystallization of glass samples

The kinetics of crystallization have been re-examined by taking into account the transient nucleation time and numerical methods were used to obtain the dependence of fraction crystallized on temperature, heating rate and nucleation conditions (temperature and time). These solutions were used to analyze the applicability of approximate models which were based on the assumption of steady state nucleation. The transient nucleation time, which precedes nucleation in as quenched samples, was taken into account to re-examine the deviations expected for relatively short nucleation time, and/or for cases when the actual nucleation temperature is displaced from the corresponding nucleation peak. Additional solutions were computed to obtain the dependence of crystallization peak temperature on the nucleation temperature. It was found that the crystallization peak temperature reaches its lowest value after nucleation at a temperature which can be significantly higher than the peak temperature of steady state nucleation.     

Re-examination of effects of nucleation temperature and time on glass crystallization

The effects of nucleation temperature and time on the kinetics of non-isothermal glass crystallization have been re-examined to demonstrate the limitations of some approximate solutions used to extract kinetic parameters from differential thermal analysis (DTA) experiments. Those features were analyzed by numerical solutions of equations describing the dependence of fraction crystallized on the rates of nucleation and growth, and the corresponding transient time, reported for lithium disilicate. It was shown that the temperature of maximum nucleation rate varies on changing the nucleation time. Some guidelines were established to assist the selection of suitable conditions to perform crystallization studies by DTA, and to extract the values of activation energy and dimensionality of growth from the dependences of crystallization peak temperature on heating rate, and nucleation time. The main limitations of these methods were identified and discussed.     

Palladium-catalyzed amination and cyclization to heteroannellated indoles and carbazoles

New ortho-bromodiarylamines in the benzo[b]thiophene series were prepared by palladium-catalyzed amination, either in the benzene or in the thiophene ring. These were submitted to palladium-catalyzed cyclization, under different required conditions, to give several differently substituted thieno[3,2-c] or [2,3-b]carbazoles and indolo[3,2-b]benzo[b]thiophenes. This constitutes a novel synthetic route to both tetracyclic systems.     

Screening of antimicrobial activity of Cistus ladanifer and Arbutus unedo extracts

In this work, the in?vitro antimicrobial activity of different crude extracts obtained from Cistus ladanifer L. and Arbutus unedo L. was investigated. The ethanol, methanol and acetone/water extracts of Cistus ladanifer and Arbutus unedo were prepared using different extraction methods and their antimicrobial activities against reference strains, including three Gram-positive, five Gram-negative and three yeasts, and against clinical isolates of Helicobacter pylori and methicillin-resistant Staphylococcus aureus, were investigated. All the extracts inhibited more than one microorganism; moreover all of them presented antimicrobial activity against the Gram-positive bacteria, Klebsiella pneumonia, Candida tropicalis and Helicobacter pylori. It is noteworthy that the most considerable in?vitro effect was observed against Helicobacter pylori. These inhibitory effects can be considered relevant to the development of new agents for inclusion in the treatment or prevention of infections by the tested strains.     

Automated analysis of lidocaine and its metabolite in plasma by in-tube solid-phase microextraction coupled with LC-UV for pharmacokinetic study

A sensitive, selective, and reproducible in-tube solid-phase microextraction and liquid chromatographic (in-tube SPME/LC-UV) method for determination of lidocaine and its metabolite monoethylglycinexylidide (MEGX) in human plasma has been developed, validated, and further applied to pharmacokinetic study in pregnant women with gestational diabetes mellitus (GDM) subjected to epidural anesthesia. Important factors in the optimization of in-tube SPME performance are discussed, including the draw/eject sample volume, draw/eject cycle number, draw/eject flow rate, sample pH, and influence of plasma proteins. The limits of quantification of the in-tube SPME/LC method were 50 ng/mL for both metabolite and lidocaine. The interday and intraday precision had coefficients of variation lower than 8%, and accuracy ranged from 95 to 117%. The response of the in-tube SPME/LC method for analytes was linear over a dynamic range from 50 to 5000 ng/mL, with correlation coefficients higher than 0.9976. The developed in-tube SPME/LC method was successfully used to analyze lidocaine and its metabolite in plasma samples from pregnant women with GDM subjected to epidural anesthesia for pharmacokinetic study.