Study of the lumiescence properties of a new series of quinolizinium salts and their interaction with DNA

The spectrofluorimetric characteristic of a new group of benzo- and methyl- quinolizinium salts at room temperature and 77 LK are reported. At room temperature, linear calibration is wide; 10^-9 M 9-cyanobenzo [a] phenathro [9,10-g] quinolizinium chloride can be detected in methanolic solution and 10^-7 M in aqueous solution. The polynuclear compounds show the most intense luminescence bands, and a significant hypsochromic shift of the fluorenscence emission maximum was observed at 77 K compared with room temperature. For the 2,3-diphenyl derivatives, the presence of a methoxy substituent produces a marked Stoke's shift, because it causes a decrease in the planarity of the molecule. The benzo compounds are similar in structure to the alkaloid coralyne, which has significant antileuikemic activity. The fused planar aromatic compounds are shown to bind with DNA.     

Three approaches to the development of selective bilayer amperometric biosensors for glucose by in situ electropolymerization

Three different glucose oxidase biosensors for the enzymatic determination of glucose, based on bilayer polymer coatings consisting of polypyrrole (PPy) and poly(o-phenylenediamine), were developed. The electrode substrates are Pt metal, carbon paste and an organic conducting salt (tetrathiafulvalene-tetracyanoquinodimethane), which introduces appreciable variability in the electrode construction process. The three sensors were compared with one another and with bare and PPy monolayer-coated sensors in terms of performance in the determination of glucose in a synthetic serum sample. These configurations provide improved selectivity against the interferences of electroactive species such as ascorbic acid and uric acid, frequently present in biological samples, and the differences between them can be taken advantage of in application to different kinds of samples.     

Synthesis and fasciolicidal activity of 5-chloro-2-methylthio-6-(1-naphthyloxy)-1H-benzimidazole

The synthesis and fasciolicidal activity of 5-chloro-2-methylthio-6-(1-naphthyloxy)-1H-benzimidazole (6) is described. Compound 6 showed 100% activity in vitro at 146.70 and 29.34 microM concentrations. It also completely removed 3-d and 10-week-old Fasciola hepatica in sheep at a dose of 15 mg/kg.     

Inter-laboratory comparison of liquid chromatographic techniques and enzyme-linked immunosorbent assay for the determination of surfactants in wastewaters

Seven laboratories participated in an inter-laboratory comparison exercise within the framework of the PRISTINE, SANDRINE and INEXsPORT European Union Projects. Solid-phase extraction (SPE) methodologies were used for the extraction of target analytes from wastewaters. The analytical strategies were based on liquid chromatography (LC) coupled to mass spectrometric (MS) or to fluorescent (FL) detection in all cases with the exception of one laboratory using a test-tube enzyme-linked immunosorbent assay kit. Samples were spiked with the surfactants nonylphenolpolyglycol ether, coconut diethanolamide, linear alkylbenzene sulfonate, nonylphenolpolyglycol ether sulfate, alkylpolyglycol ether and secondary alkane sulfonate. After enrichment on previously conditioned SPE cartridges, the SPE cartridges were distributed among the participating laboratories without the information about the amount of spiked surfactants. In addition, SPE cartridges loaded with a real-world environmental sample containing a tannery wastewater were also analyzed. The results of the programme showed that SPE followed by LC-MS techniques are reliable for the surfactants determination at submicrogram to microgram per liter levels in wastewaters. Inter-laboratory precision values were calculated as the reproducibility relative standard deviation (RSD(R)) which was determined from the reproducibility standard deviation (sR) and the average concentration at a particular concentration level. When data from all laboratories were pooled, the RSD(R) values ranged from 5.1 to 28.3% for the determination of target analytes. The most accurate result corresponded to that given for linear alkylbenzene sulfonates. Taking into account that different methodologies were used (including non-chromatographic techniques) and the complexity of the samples analyzed, it can be considered that acceptable reproducibility values were obtained in this inter-laboratory study.     

Enantiomeric composition studies in Lavandula species using supercritical fluids

Characteristic aroma compounds in plants and essential oils of Lavandula from different varieties were examined. The study of the qualitative and quantitative composition of the major volatile components was faced by developing a method based on the use of supercritical fluid extraction-GC-MS (SFE-GC-MS). The optimization of a variety of parameters affecting SFE extraction enabled RSDs from three replicates lower than 2% to be achieved. Equally, recoveries of up to 59% were obtained by applying the proposed method. The use of multidimensional GC was necessary to enantiomerically resolve the target compounds. The obtained results showed enantiomeric purities >90% for all studied compounds in all varieties considered, proving the natural invariability of the enantiomeric composition of the compounds of interest. This information can be useful in authenticity studies as well as in selecting natural sources of enantiomerically pure compounds.     

Gaseous sample introduction for the determination of silicon by ICP-AES

The generation of volatile species of silicon as a means to introduce silicon into an inductively coupled plasma has been studied. It is based on the reaction between silicon and fluoride ions in sulfuric acid media and it was carried out using different flow injection mountings. The first mounting works with an injection of 100 μL concentrated sulfuric acid and 150 μL silicon standard solution in a continuous 0.05 mol L^–1 NaF solution flow. The method shows a linear response between the intensity of emission at 251.611 nm line and the silicon concentration from 0.1 to 200 μg mL^–1, with a reproducibility of 2% and a detection limit of 0.004 μg mL^–1. The second mounting produces the volatile species by the reaction between two opposed aerosol flows in a home-made nebulization chamber. This chamber has a Cross-Flow and a Meinhard nebulizer at either end. A linear response ranging from 0.1 to 1000 μg mL^–1 of silicon solution is obtained and the reproducibility rises to 8%.The detection limit reached is 0.02 μg mL^–1. The silicon content in real water samples was determined by applying both the above-mentioned methods and a third method for reference. Received: 6 November 1996 / Revised: 19 December 1996 / Accepted: 3 January 1997     

Micellar electrokinetic capillary chromatography as an alternative method for the determination of ethinylestradiol and levo-norgestrel

A method for quantifying of ethinylestradiol (ETE) and levo-norgestrel (LEV) in pharmaceutical products by micellar electrokinetic chromatography (MEKC) is described. The separation was carried out at 25 degrees C and 25 kV, using a 20 mM borate buffer (pH 9.2), 15 mM sodium dodecylsulfate (SDS) in 30% acetonitrile/water (v/v). Under these conditions the analysis takes about 7 min. The method has been applied for quantifying both compounds in six different commercial contraceptives and the proposed method gave good results when compared with a reference liquid chromatographic (LC) method.     

Study of a fluorometric-enzymatic method for bilirubin based on chemically modified bilirubin-oxidase and multivariate calibration

The chemical derivatization of bilirubin oxidase (BOx) with a fluorescein derivative (FS) yields a chemically modified enzyme (BOx-FS), with excitation and emission maxima at 487 and 520 nm, respectively. During the oxygen oxidation reaction of bilirubins, in the presence of the modified enzyme, the change in the fluorescence of the modified enzyme depends on the concentration and type of bilirubin. This effect can be used for analytical purposes. Firstly, a theoretical-experimental study of the analytical system was carried out. The mechanism responsible for the fluorescence variation was clarified, a mathematical model developed and the variables affecting the fluorescence changes optimized. The concentration ranges in which the model can be applied (up to 12 mg bilirubin l(-1)), and the precision of the measurement (about 4%) were established for the three bilirubins. The application of the methodology to the simultaneous determination of direct and total bilirubins were studied by applying multivariate calibration methods to the whole kinetic profiles. A reduced calibration matrix (derived from a 5(3) base matrix) is proposed for calibration and different numerical methods were tested: Principal Components Regression (PCR), Partial Least Squares Regression (PLS) and Artificial Neural Networks (ANN). The simultaneous determination of direct and total bilirubin (average validation errors of about 9 and 10%, respectively) can be carried out from a single run. Furthermore, a semi-quantitative speciation of the three bilirubins (free, conjugated and albumin-bonded bilirubin) may be simultaneously obtained.     

Bivariate distributions with Weibull conditionals

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New In-Situ Sampling and Analysis of the Production of CeO<Subscript>2</Subscript> Powders from Liquid Precursors in a rf Thermal Plasma Reactor. Part 2: Analysis of CeO<Subscript>2</Subscript> Powders,Fuel Addition,and Image Analysis

A novel reactor design, sampling probe and wet collection system were used to investigate the combined effects of plasma operating parameters and particle collection mechanisms on the synthesis of CeO₂ particles from liquid precursors. The sampling of particles in-flight and the collection of particles at several reactor regions were used to provide experimental evidence of particle size at different reactor locations at various plasma operating conditions, i.e., power and plasma gas flow rates. This information provided a picture of how CeO₂ particles were formed and how these particles were collected in various locations. The effect of adding water-soluble fuels (alanine and glycine) to the original cerium nitrate solutions was also investigated. Fuel addition decreased the temperature of CeO₂ formation by acting as a local heat source as a result of fuel auto-ignition. Photographs of the particles in-flight were taken using a fast speed CCD camera.