Biocompatible in-tube solid phase microextraction coupled with liquid chromatography-fluorescence detection for determination of interferon alpha in plasma samples

The present work demonstrates the successful application of automated biocompatible in-tube solid-phase microextraction coupled with liquid chromatography (in-tube SPME/LC) for determination of interferon alpha(2a) (IFN alpha(2a)) in plasma samples for therapeutic drug monitoring. A restricted access material (RAM, protein-coated silica) was employed for preparation of a lab-made biocompatible in-tube SPME capillary that enables the direct injection of biological fluids as well as the simultaneous exclusion of macromolecules by chemical diffusion barrier and drug pre-concentration. The in-tube SPME variables, such as sample volume, draw/eject volume, number of draw-eject cycles, and desorption mode were optimized, to improve the sensitivity of the proposed method. The IFN alpha(2a) analyses in plasma sample were carried out within 25 min (sample preparation and LC analyses). The response of the proposed method was linear over a dynamic range, from 0.06 to 3.0 MIU mL(-1), with correlation coefficient equal to 0.998. The interday precision of the method presented coefficient of variation lower than 8%. The proposed automated method has adequate analytical sensitivity and selectivity for determination of IFN alpha(2a) in plasma samples for therapeutic drug monitoring. (C) 2010 Elsevier B.V. All rights reserved.

Fluoxetine and norfluoxetine analysis by direct injection of human plasma in a column switching liquid chromatographic system

A column switching LC method is presented for the analysis of fluoxetine (FLU) and norfluoxetine (NFLU) by direct injection of human plasma using a lab-made restricted access media (RAM) column. A RAM-BSA-octadecyl silica (C-18) column (40 min x 4.6 mm, 10 mu m) is evaluated in both backflush and foreflush elution modes and coupled with a C-18 lab-made (50 mm x 4.6 mm, 3 pm) analytical column in order to perform online sample preparation. Direct injection of 100 mu L, of plasma samples is possible with the developed approach. In addition, reduction of sample handling is obtained when compared with traditional liquid-liquid extraction (LLE) and SPE. The total analysis time is around 20 min. A LOQ of 15 ng/mL is achieved in a concentration range of 15-500 ng/mL, allowing the therapeutic drug monitoring of clinical samples. The precision values achieved are lower than 15% for all the evaluated points with adequate recovery and accuracy. Furthermore, no matrix interferences are found in the analysis and the proposed method shows to be an adequate alternative for analysis of FLU in plasma.

Combining Monte Carlo simulation and density-functional theory to describe the spectral changes of Na(2) in liquid helium

Spectral changes of Na(2) in liquid helium were studied using the sequential Monte Carlo-quantum mechanics method. Configurations composed by Na(2) surrounded by explicit helium atoms sampled from the Monte Carlo simulation were submitted to time-dependent density-functional theory calculations of the electronic absorption spectrum using different functionals. Attention is given to both line shift and line broadening. The Perdew, Burke, and Ernzerhof (PBE1PBE, also known as PBE0) functional, with the PBE1PBE/6-311++G(2d,2p) basis set, gives the spectral shift, compared to gas phase, of 500 cm(-1) for the allowed X (1)Sigma(+)(g) -> B (1)Pi(u) transition, in very good agreement with the experimental value (700 cm(-1)). For comparison, cluster calculations were also performed and the first X (1)Sigma(+)(g) -> A (1)Sigma(+)(u) transition was also considered.

High performance magnetic separation of gold nanoparticles for catalytic oxidation of alcohols

We present the magnetic separation approach to facilitate the recovery of gold nanoparticle (AuNP) catalysts. The use of magnetically recoverable supports for the immobilization of AuNPs instead of traditional oxides, polymers or carbon based solids guarantees facile, clean, fast and efficient separation of the catalyst at the end of the reaction cycle. Magnetic separation can be considered an environmentally benign separation approach, since it minimizes the use of auxiliary substances and energy for achieving catalyst recovery. The catalyst preparation is based on the immobilization of Au(3+) on the surface of core-shell silica-coated magnetite nanoparticles, followed by metal reduction using two different methods. AuNPs were prepared by thermal reduction in air and by hydrogen reduction at mild temperature. Interestingly, the mean particle size of the supported AuNPs was similar (ca. 5.9 nm), but the polydispersity of the samples is quite different. The catalytic activity of both catalysts in the aerobic oxidation of alcohols was investigated and a distinct selectivity for benzyl alcohol oxidation was observed.

Molecular dynamics simulation of liquid trimethylphosphine

Structural and dynamical properties of liquid trimethylphosphine (TMP), (CH(3))(3)P, as a function of temperature is investigated by molecular dynamics (MD) simulations. The force field used in the MD simulations, which has been proposed from molecular mechanics and quantum chemistry calculations, is able to reproduce the experimental density of liquid TMP at room temperature. Equilibrium structure is investigated by the usual radial distribution function, g(r), and also in the reciprocal space by the static structure factor, S(k). On the basis of center of mass distances, liquid TMP behaves like a simple liquid of almost spherical particles, but orientational correlation due to dipole-dipole interactions is revealed at short-range distances. Single particle and collective dynamics are investigated by several time correlation functions. At high temperatures, diffusion and reorientation occur at the same time range as relaxation of the liquid structure. Decoupling of these dynamic properties starts below ca. 220 K, when rattling dynamics of a given TMP molecules due to the cage effect of neighbouring molecules becomes important. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3624408]

Linear viscoelasticity of styrenic block copolymers-clay nanocomposites

In this work, the rheological behavior of block copolymers with different morphologies (lamellar, cylindrical, spherical, and disordered) and their clay-containing nanocomposites was studied using small amplitude oscillatory shear. The copolymers studied were one asymmetric starblock styrene-butadiene-styrene copolymer and four styrene-ethylene/butylenes-styrene copolymers with different molecular architectures, one of them being modified with maleic anhydride. The nanocomposites of those copolymers were prepared by adding organophilic clay using three different preparation techniques: melt mixing, solution casting, and a hybrid melt mixing-solution technique. The nanocomposites were characterized by X-ray diffraction and transmission electron microscopy, and their viscoelastic properties were evaluated and compared to the ones of the pure copolymers. The influence of copolymer morphology and presence of clay on the storage modulus (G`) curves was studied by the evaluation of the changes in the low frequency slope of log G` x log omega (omega: frequency) curves upon variation of temperature and clay addition. This slope may be related to the degree of liquid- or solid-like behavior of a material. It was observed that at temperatures corresponding to the ordered state, the rheological behavior of the nanocomposites depended mainly on the viscoelasticity of each type of ordered phase and the variation of the slope due to the addition of clay was small. For temperatures corresponding to the disordered state, however, the rheological behavior of the copolymer nanocomposites was dictated mostly by the degree of clay dispersion: When the clay was well dispersed, a strong solid-like behavior corresponding to large G` slope variations was observed.

Batch Liquid-Liquid Extraction of Phenol from Aqueous Solutions

The aim of this work is the study of batch liquid-liquid extraction of phenol from aqueous solutions in a bench-scale well-mixed reactor. The influence of the ratio of phase volumes, temperature, and rotational speed on phenol removal (0.72-1.1% w/w) was investigated using methyl isobutyl ketone as an extracting solvent. For this purpose, the ratio of phase volumes were set at 0.1 and 0.2, the temperature at 10, 20, and 30 degrees C, and the rotational speed at 300, 400, and 500 rpm. A physical model based on the material balance of the phases as well as the equation of mass flux between the phases allowed the estimation of the overall coefficient of mass transfer coupled with the superficial area. Moreover, it proved to fit, satisfactorily well, the experimental data of residual phenol concentration in the organic phase versus time under all the conditions investigated.

Liquid-Liquid Equilibrium of Aqueous Two-Phase Systems Containing Some Synthetic Polyelectrolytes and Polyethylene Glycol

Experimental results are presented for the liquid-liquid equilibrium of aqueous two-phase systems containing a synthetic polyelectrolyte (polysodium acrylate, polysodium methacrylate, and polysodium ethylene sulfonate) and polyethylene glycol at (298.2 and 323.2) K. A total of 40 phase diagrams were obtained, comprising data both of the binodal curve (obtained through cloud-point measurements) and of equilibrium compositions. The influences of temperature, the nature of the polyelectrolyte monomer unit, and the chain length of both types of polymers are analyzed and discussed.

Photo-Fenton removal of water-soluble polymers

This paper presents the results of experiments carried out in a laboratory-scale photochemical reactor on the photodegradation of different polymers in aqueous solutions by the photo-Fenton process. Solutions of three polymers, polyethyleneglicol (PEG), polyacrylamide (PAM), and polyvinylpyrrolidone(PVP), were tested under different. conditions. The reaction progress was evaluated by sampling and analyzing the total organic carbon concentration in solution (TOC) along the reaction time. The behavior of the different polymers is discussed, based oil the evolution of the TOC-time curves. Under specific reaction conditions, the formation and coalescence of solid particles was Visually observed. Solids formation occurred simultaneously to a sharp decrease in the TOC of the liquid phase. This may be favorable for the treatment of industrial wastewater containing polymers, since the photodegradation process can be Coupled with solid separation systems. which may reduce the treatment cost. (C) 2008 Elsevier B.V. All rights reserved.

Effect of Charge Asymmetry on Adsorption and Phase Separation of Polyampholytes on Silica and Cellulose Surfaces

The relation between the properties of polyampholytes in aqueous solution and their adsorption behaviors on silica and cellulose surfaces was investigated. Four polyampholytes carrying different charge densities but with the same nominal ratio of positive to negative segments and two structurally similar polyelectrolytes (a polyacid and a polybase) were investigated by using quartz crystal microgravimetry using silica-coated and cellulose-coated quartz resonators. Time-resolved mass and rigidity (or viscoelasticity) of the adsorbed layer was determined from the shifts in frequency (Delta f) and energy dissipation (Delta D) of the respective resonator. Therefore, elucidation of the dynamics and extent of adsorption, as well as the conformational changes of the adsorbed macromolecules, were possible. The charge properties of the solid Surface played a crucial role in the adsorption of the studied polyampholytes, which was explained by the capability of the surface to polarize the polyampholyte at the interface. Under the same experimental conditions, the polyampholytes had a higher nominal charge density phase-separated near the interface, producing a soft, dissipative, and loosely bound layer. In the case of cellulose substrates, where adsorption was limited, electrostatic and polarization effects were concluded to be less significant.

Determination of eight fatty acid ethyl esters in meconium samples by headspace solid-phase microextraction and gas chromatography-mass spectrometry

A number of fatty acid ethyl esters (FAEEs) have recently been detected in meconium samples. Several of these FAEEs have been evaluated as possible biomarkers for in utero ethanol exposure. In the present study, a method was optimized and validated for the simultaneous determination of eight FAEEs (ethyl laurate, ethyl myristate, ethyl palmitate, ethyl palmitoleate, ethyl stearate, ethyl oleate, ethyl linoleate and ethyl arachidonate) in meconium samples. FAEEs were extracted by headspace solid-phase microextraction. Analyte detection and quantification were carried out using GC-MS operated in chemical ionization mode. The corresponding D5-ethyl esters were synthesized and used as internal standards. The LOQ and LOD for each analyte were <150 and <100 ng/g, respectively. The method showed good linearity (r(2)>0.98) in the concentration range studied (LOQ -2000 ng/g). The intra- and interday imprecision, given by the RSD of the method, was lower than 15% for all FAEEs studied. The validated method was applied to 63 authentic specimens. FAEEs could be detected in alcohol-exposed newborns ( >600 ng/g cumulative concentration). Interestingly, FAEEs could also be detected in some non-exposed newborns, although the concentrations were much lower than those measured in exposed cases.

Methods for detection of anatoxin-a(s) by liquid chromatography coupled to electrospray ionization-tandem mass spectrometry

Anatoxin-a(s) is a potent irreversible inhibitor of the enzyme acetylcholinesterase with a unique N-hydroxyguanidine methylphosphate ester chemical structure. Determination of this toxin in environmental samples is hampered by the lack of specific methods for its detection. Using the toxic strain of Anabaena lemmermani PH-160 B as positive control, the fragmentation characteristics of anatoxin-a(s) under collision-induced dissociation conditions have been investigated and new LC-MS/MS methods proposed. Recommended ion transitions for correct detection of this toxin are 253 > 58, 253 > 159, 235 > 98 and 235 > 96. Chromatographic separation is better achieved under HILIC conditions employing a ZIC-HILIC column. This method was used to confirm for the first time the production of anatoxin-a(s) by strains of Anabaena oumiana ITEP-025 and ITEP-026. Considering no standard solutions are commercially available, our results will be of significant use for the correct identification of this toxin by LC-MS/MS. (C) 2009 Elsevier Ltd. All rights reserved.

Separation of Steroids and the Determination of Estradiol Content in Transdermic Patches by Microemulsion Electrokinetic Chromatography

A novel microemulsion electrokinetic capillary chromatography (MEEKC) method has been developed which separates a range of nine steroids. A microemulsion containing ethyl acetate, butan-1-ol, sodium dodecyl sulfate, 15% (v/v) acetonitrile and 12 mmol L(-1) sodium tetraborate aqueous buffer at pH 9.2 was used with direct UV detection at 200 nm. The method was validated for the determination of 17 beta-estradiol content, a hormone steroid, in transdermal patches. Adequate sensitivity (DL = 0.88 mu g mL(-1); QL = 2.65 mu g mL(-1)) without interference from sample excipients was obtained. 17 beta-Estradiol migrates in approximately 5.4 min. Estrone was used as internal standard and acceptable precision (< 1.2% RSD), linearity (r = 0.9996; range from 40.0 to 60.0 mu g mL(-1)), and recovery (100.4 +/- A 0.9% at three concentration levels) were obtained. The principal advantage of the method is that it is rapid and avoids the need of time consuming and expensive sample pre-treatment steps.

LC-UV Methodology for Simultaneous Determination of Lamivudine and Zidovudine in Plasma by Liquid-Liquid Extraction

This study describes an accurate, sensitive, and specific chromatographic method for the simultaneous quantitative determination of lamivudine and zidovudine in human blood plasma, using stavudine as an internal standard. The chromatographic separation was performed using a C8 column (150 x 4.6 mm, 5 mu m), and ultraviolet absorbency detection at 270 nm with gradient elution. Two mobile phases were used. Phase A contained 10 mM potassium phosphate and 3% acetonitrile, whereas Phase B contained methanol. A linear gradient was used with a variability of A-B phase proportion from 98-2% to 72-28%, respectively. The drug extraction was performed with two 4 mL aliquots of ethyl acetate.

Simultaneous determination of econazole nitrate, main impurities and preservatives in cream formulation by high performance liquid chromatography

A reversed-phase high performance liquid chromatographic (RP-HPLC) method for determination of econazole nitrate, preservatives (methylparaben and propylparaben) and its main impurities (4-chlorobenzl alcohol and alpha-(2,4-dicholorophenyl)-1H-imidazole-1-ethanol) in cream formulations, has been developed and validated. Separation was achieved on a column Bondclone (R) C18 (300 mm x 3.9 mm i.d., 10 mu m) using a gradient method with mobile phase composed of methanol and water. The flow rate was 1.4 mL min(-1), temperature of the column was 25 C and the detection was made at 220 nm. Miconazole nitrate was used as an internal standard. The total run time was less than 15 min, The analytical curves presented coefficient of correlation upper to 0.99 and detection and quantitation limits were calculated for all molecules. Excellent accuracy and precision were obtained for econazole nitrate. Recoveries varied from 97.9 to 102.3% and intra- and inter-day precisions, calculated as relative standard deviation (R.S.D), were lower than 2.2%. Specificity, robustness and assay for econazole nitrate were also determined. The method allowed the quantitative determination of econazole nitrate, its impurities and preservatives and could be applied as a stability-indicating method for econazole nitrate in cream formulations. (C) 2008 Elsevier B.V. All rights reserved.