1,720,965 research outputs found
Chiral separation of pesticides by coupled-column liquid chromatography application to the stereoselective degradation of fenvalerate in soil
No full textChiral separation of synthetic pesticides presenting more than one center of asymmetry was performed by multidimensional liquid chromatography. The method consisted of coupling two columns by means of a six‐port valve: an achiral column was used for the separation of the pesticide diastereomers, that were, then, individually switched into the chiral column and resolved as the corresponding enantiomers. In order to obtain optimum resolution conditions for pesticides existing as four (fenvalerate, propiconazole, and triadimenol) and eight (cyfluthrin) optical isomers, a number of coupled‐column systems constituted of an achiral (plain silica gel, γ‐cyanopropyl(CNP)‐, and γ‐aminopropyl(AMP)‐silanized silica gel) and a chiral [containing cellulose tris‐(3,5‐dimethylphenyl‐carbamate), (R)(−)‐N‐(3,5‐dinitrobenzoyl)‐phenylglycine(DNBPG), and (S)‐N‐1‐(α‐naphthyl) ethylaminocarbonyl‐(S)‐ter‐leucine, as the selectors] stationary phases were studied. Coupled‐column liquid chromatography (CC‐LC) proved to be a very effective strategy allowing the full resolution, with the exception of triadimenol, of all the investigated pesticides. The method was used for studying the stereoselective degradation of fenvalerate in soil under simulated laboratory conditions
Caratterizzazione di un sensore a membrana di chitosano per la determinazione del Cromo (III) nelle acque di concia
No full textAnalysis of drugs of forensic interest with Capillary Zone Electrophoresis / Time-of-Flight Mass Spectrometry based on the use of non-volatile buffers
No full textThe present work is aimed at investigating the influence of the background electrolyte composition and concentration on the separation efficiency and resolution and mass spectrometric detection of illicit drugs in a CZE-ESI-TOF MS system. The effect of phosphate, borate and Tris buffers on the separation and mass spectrometry response of a mixture of 3,4-methylenedioxyamphetamine, 3,4-methylenedioxymethamphetamine, methadone, cocaine, morphine, codeine and 6-monoacethylmorphine was studied, in comparison with a reference ammonium formate separation buffer. Inorganic non volatile borate and Tris buffers proved hardly suitable for CE-MS analysis, but quite unexpectedly ammonium phosphate buffers showed good separation and ionization performances for all the analytes tested. Applications of this method to real samples of hair from drug addicts are also provided
Capillary electrochromatographic separation of illicit drugs employing a cyano stationary phase
No full textIn this study, we present a capillary electrochromatographic method for separation of basic compounds of interest in forensic science (amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine, 3,4-methylenedioxymethamphetamine, 3,4-methylenedioxyethylamphetamine, cocaine, codeine, heroin, morphine, and 6-monoacethylmorphine). Several analytical conditions were taken into account to completely separate in the same run the 10 drugs of abuse analyzed. Chromatographic retention, selectivity and efficiency were evaluated in dependence of the type of stationary phase (CN and RP-C18 derivatized silica particles), mobile phase composition, buffer type and pH, sample injection. The optimum separation parameters were set up using a mixture of aqueous sodium phosphate buffer (pH 2.5)/acetonitrile (80/20, v/v) as the mobile phase, 10 kV and 20 °C as applied voltage and capillary temperature, respectively. Under these conditions all the studied analytes were baseline resolved within 20 min. The method performance was investigated in terms of precision, linearity, sensitivity and accuracy to demonstrate the applicability of the developed capillary electrochromatographic system to forensic analysis. Calibration curves provided a good linearity over a working range of 100-1200 ng/mL for all analytes. Limits of detection and quantification were in the range 5-12 ng/mL and 10-30 ng/mL, respectively. Then the method was applied to the analysis of a human urine sample spiked with a basic compounds' mixture. Urine samples' pre-treatment was carried out through a solid phase extraction (SPE) procedure on strong cation exchange (SCX) cartridges
Use of Hepta Tyr glycopeptide antibiotic as chiral selector in capillary electrophoresis.
No full textA new glycopeptide antibiotic, MDL 63,246 (Hepta-tyr), of the teicoplanin family, has been evaluated in capillary electrophoresis for the resolution of chiral compounds of pharmaceutical and environmental interest. Electrophoretic separations were carried out in a polyacrylamide-coated capillary using the partial filling-counter current mode with aqueous-organic buffers in the pH range 4-6. Experimental parameters affecting resolution, such as antibiotic concentration, buffer pH, organic modifier type and capillary temperature, were studied. The Hepta-tyr antibiotic exhibited a high enantiorecognition capability towards the studied compounds at very low concentrations (1-2 mg/mL). The optimum experimental conditions were achieved by using a buffer at pH 5 containing acetonitrile at 25 degrees C
CEC-ESI ion trap MS of multiple drugs of abuse
No full textThis article describes a method for the separation and determination of nine drugs of abuse in human urine, including amphetamines, cocaine, codeine, heroin and morphine. This method was based on SPE on a strong cation exchange cartridge followed by CEC-MS. The CEC experiments were performed in fused silica capillaries (100 m×30 cm) packed with a 3 m cyano derivatized silica stationary phase. A laboratory-made liquid junction interface was used for CEC-MS coupling. The outlet capillary column was connected with an emitter tip that was positioned in front of the MS orifice. A stable electrospray was produced at nanoliter per minute flow rates applying a hydrostatic pressure (few kPa) to the interface. The coupling of packed CEC columns with mass spectrometer as detector, using a liquid junction interface, provided several advantages such as better sensitivity, low dead volume and independent control of the conditions used for CEC separation and ESI analysis. For this purpose, preliminary experiments were carried out in CEC-UV to optimize the proper mobile phase for CEC analysis. Good separation efficiency was achieved for almost all compounds, using a mixture containing ACN and 25 mM ammonium formate buffer at pH 3 (30:70, v/v), as mobile phase and applying a voltage of 12 kV. ESI ion-trap MS detection was performed in the positive ionization mode. A spray liquid, composed by methanol-water (80:20, v/v) and 1% formic acid, was delivered at a nano-flow rate of 200 nL/min. Under optimized CEC-ESI-MS conditions, separation of the investigated drugs was performed within 13 min. CEC-MS and CEC-MS2 spectra were obtained by providing the unambiguous confirmation of these drugs in urine samples. Method precision was determined with RSDs values 3.3% for retention times and 16.3% for peak areas in both intra-day and day-to-day experiments. LODs were established between 0.78 and 3.12 ng/mL for all compounds. Linearity was satisfactory in the concentration range of interest for all compounds (r20.995). The developed CEC-MS method was then applied to the analysis of drugs of abuse in spiked urine samples, obtaining recovery data in the range 80-95%
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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