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At least 1,153 records · Page 64Linked to original sources
PubMed2001

Selective continuous monitoring and analysis of mixtures of acesulfame-K, cyclamate, and saccharin in artificial sweetener tablets, diet soft drinks, yogurts, and wines using filter-supported bilayer lipid membranes.

This work describes a technique for the rapid and sensitive electrochemical flow injection monitoring and analysis of mixtures of the artificial sweeteners acesulfame-K, cyclamate, and saccharin using stabilized systems of filter-supported bilayer lipid membranes (BLMs). Injections of artificial sweeteners were made into flowing streams of a carrier electrolyte solution, and a transient current signal with duration of seconds reproducibly appeared in less than < 1 min after exposure of the lipid membranes to the artificial sweeteners. The magnitude of this signal was linearly related to the concentration of artificial sweeteners, which could be determined at micromolar levels. Repetitive cycles of injection of artificial sweeteners have shown no signal degradation during each cycle (30 sequential injections). The time of appearance of the transient response was different for each artificial sweetener and increased in the order of cyclamic acid, acesulfame-K, and saccharin. The difference in time of response has allowed selective detection and analysis of these artificial sweeteners in mixtures. The effect of potent interferences, including a wide range of compounds usually found in foods, proteins, and lipids was investigated. The results showed no interferences from these constituents of real food samples. The major interference from proteins (most common in lipid-film-based biosensors) can be eliminated by modulation of the carrier solution that does not allow adsorption of these compounds in BLMs. The technique was applied in real food samples, that is, in artificial sweetener tablets, diet soft drinks, wines, and yogurts that contain mixtures of these artificial sweeteners with aspartame and other compounds. A comparison of results using the present method and that of an Official Method of Analysis showed good agreement between the two methods.

Beverages↗
PubMed2005

Optimizing an ultrafast generic high-performance liquid chromatography/tandem mass spectrometry method for faster discovery pharmacokinetic sample throughput.

For higher throughput screening, where the number of new chemical entities (NCEs) to test is rapidly increasing, fast sample turnaround time is essential. In order to increase efficiency a generic high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) method, with a cycle time of 85 s (42 injections/h), was created. This was accomplished through the use of a 1-min ballistic gradient and the optimization of the autosampler. The gradient was optimized by varying the organic mobile phase concentration and examining its ballistic characteristics with respect to matrix ion suppression and compound retention time. The autosampler time could be reduced by optimizing several parameters and by determining the source of most of the carryover in order to reduce the number of syringe and injector washes. Finally, the reliability of the new generic method is demonstrated by comparison of sample data with a standard 2-min linear gradient method that showed that the data sets were well correlated. For plasma AUC (ng.h/mL) of 28 NCEs, the regression line had a slope of 0.92 and the R2 was 0.929. The described method was found to be useful for both rat plasma and tissue samples.

Animals↗
PubMed2005

Electroanalytical study of the antidepressant sertraline.

A flow injection square wave cathodic stripping voltammetric method has been developed for the determination of sertraline in a pharmaceutical preparation. The method shows linearity between peak current intensity and sertraline concentration for the interval between 0.20 x 10(-6) and 1.20 x 10(-6) mol L(-1). Limits of detection and quantification were found to be 1.5 x 10(-7) and 5.0 x 10 (-7) mol L(-1), respectively. Up to 70 samples per hour can be analysed with a good precision (R.S.D. = 2.5%). The proposed method was successfully applied to the determination of sertraline in a commercial product. In the voltammetric determination of sertraline in flow, a high sample rate is obtained at reduced costs, opening the possibility to compete with the chromatographic methods generally used for this analysis.

Electrochemistry↗
PubMed2006

Determination of drugs in biological fluids by direct injection of samples for liquid-chromatographic analysis.

The analysis of drugs in various biological fluids is an important criterion for the determination of the physiological performance of a drug. After sampling of the biological fluid, the next step in the analytical process is sample preparation. The complexity of biological fluids adds to the challenge of direct determination of the drug by chromatographic analysis, therefore demanding a sample preparation step that is often time-consuming, tedious, and frequently overlooked. However, direct on-line injection methods offer the advantage of reducing sample preparation steps and enabling effective pre-concentration and clean-up of biological fluids. These procedures can be automated and therefore reduce the requirements for handling potentially infectious biomaterial, improve reproducibility, and minimize sample manipulations and potential contamination. The objective of this review is to present an overview of the existing literature with emphasis on advances in automated sample preparation methods for liquid-chromatographic methods. More specifically, this review concentrates on the use of direct injection techniques, such as restricted-access materials, turbulent-flow chromatography and other automated on-line solid-phase extraction (SPE) procedures. It also includes short overviews of emerging automated extraction-phase technologies, such as molecularly imprinted polymers, in-tube solid-phase micro-extraction, and micro-extraction in a packed syringe for a more selective extraction of analytes from complex samples, providing further improvements in the analysis of biological materials. Lastly, the outlook for these methods and potential new applications for these technologies are briefly discussed.

Body Fluids↗
PubMed2006

Improvements on the electrokinetic injection technique for microfluidic chips.

This paper presents a T-form electrokinetic injection system for the discrete time-based loading and dispensing of samples of variable-volume in a microfluidic chip. A novel push-pull effect is produced during the loading and dispensing processes by the application of an appropriate control voltage distribution. The experimental and numerical results show that this push-pull loading technique produces compact sample plugs and hence improves the detection resolution of the microfluidic device. The injection system is integrated with a microflow switch, and a suitable voltage control scheme is proposed to guide the sample to the desired outlet port such that the microfluidic device can function as a microdispenser. The time-based variable-volume T-form injection method presented in this study is performed using a compact geometry and a simple control scheme and can be readily integrated with other microfluidic devices to form a microfluidic system capable of continuous monitoring and analysis of bioreactions in the life science and biochemistry fields.

Electrophoresis, Microchip↗
PubMed2005

Automatic determination of phylloquinone in vegetables and fruits using on-line photochemical reduction and fluorescence detection via solid phase extraction and flow injection.

A very simple, rapid and highly sensitive flow injection fluorimetric method was developed for the determination of phylloquinone. The assay was based on the on-line reduction of phylloquinone in dodecylsulfate micelles after irradiation with UV light. The micellar medium enhanced the fluorescence and stability of the reduced phylloquinone. Under optimum experimental conditions, the range of application of the technique was between 0.09 and 45.0 microg mL(-1) and the detection limit was 0.05 microg mL(-1). The sample throughput was 90 injections per hour. The reliability of the method for the routine analysis of phylloquinone in vegetables and fruits is demonstrated. Extractions were made with hexane, and an automated solid phase extraction system was used to purify the sample extracts prior to injection into the flow injection manifold.

Calibration↗
PubMed2003

On-line coupling of sequential injection extraction with restricted-access materials for sample clean-up and analysis of drugs in biological matrix.

In this contribution, the on-line coupling of solid phase extraction (SPE), based on a restricted-access material (RAM), with sequential injection technique (SIA) for the analysis of biological samples, is described. The SIA-RAM system was tested with a new potential antileucotrienic drug (VUFB-19363 (Quinlukast)) for serum analysis. The method is based on SPE with the novel internal-surface reversed-phase column packing material-alkyl-diol silica (ADS). The supports tolerate direct and repetitive injection of proteinaceous fluids (plasma, serum) and allow reversed-phase partitioning at the internal surface. A column packed with a 25 microm C18 alkyl-diol support was used for direct serum injection. Using a 6-port selection valve and the system of three mobile phases, the polar matrix compounds and metabolites are removed by sequentially aspirated mobile phases with lower content of the organic part (methanol-water (2:98) and following acetonitrile-water (20:80)) to the waste, and then, the analyte enriched on the column is eluted by a strong mobile phase (acetonitrile-methanol-water (40:20:40)) to the UV detector without transfer loss. With the fully automated SIA system, a total analysis time of less than 10 min was achieved. The only off-line sample pre-treatment step required to remove particulate matter was centrifugation. The studies showed a range of linearity (2-40 microg ml(-1)) and a high recovery (93.6-96.8%) of drug from the biological matrix with coefficients of variation (RSD) less than 5.0% (n = 6). This paper introduces a new, simple and robust analytical technique suitable for screening determination and direct analysis of drugs in biological materials.

Drug Contamination↗
PubMedDate not supplied

The production and characterization of anti-bovine CD14 monoclonal antibodies.

To characterize further the chemical and biological properties of bovine soluble (bos) CD14, a panel of ten murine monoclonal antibodies (mAb) reactive with recombinant (r) bosCD14 were produced. A sandwich ELISA, using murine mAb and rabbit polyclonal antibodies reactive with rbosCD14 was developed. All the mAb were reactive by ELISA with baculovirus-derived rbosCD14 and they recognized rbosCD14 (40 kDa) by western blot analysis. The mAb also identified by western blot sCD14 (53 and 58 kDa) in milk and blood and sCD14 (47 kDa) in a lysate of macrophages obtained from involuted bovine mammary gland secretions. Analysis by ELISA of whey samples after intramammary injection of lipopolysaccharide (LPS) (10 micro g) revealed increased sCD14 levels between 8 to 48 h after injection. Flow cytometric analysis showed that the mAb bound to macrophages isolated from involuted mammary gland secretions and mouse macrophages but not to swine or horse monocytes. Addition of anti-rbosCD14 mAb to monocytes stimulated with LPS reduced in vitro production of TNF-alpha. The anti-rbosCD14 antibodies generated in this study will be useful in studying CD14, an accessory molecule that contributes to host innate recognition of bacterial cell wall components in mammary secretions produced during mastitis.

Animals↗
PubMed2003

Measurement and modeling of ozone and nitrogen oxides produced by laser breakdown in oxygen-nitrogen atmospheres.

The production of ozone nad nitrogen oxides was studied during multiple laser breakdown in oxygen-nitrogen mixtures at atmospheric pressure. About 2000 laser shots at 10(10) W cm-2 were delivered into a sealed reaction chamber. The chamber with a long capillary was designed to measure absorption of O3, NO, and NO2 as a function of the number of laser shots. The light source for absorption measurements was the continuum radiation emitted by the plasma during the first 0.2 microsecond of its evolution. A kinetic model was developed that encompassed the principal chemical reactions between the major atmospheric components and the products of laser breakdown. In the model, the laser plasma was treated as a source of nitric oxide and atomic oxygen, whose rates of production were calculated using measured absorption by NO, NO2, and O3. The calculated concentration profiles for NO, NO2, and O3 were in good agreement with measured profiles over a time scale of 0-200 s. The steady-state concentration of ozone was measured in a flow cell in air. For a single breakdown in air, the estimated steady-state yield of ozone was 2 x 10(12) molecules, which agreed with the model prediction. This study can be of importance for general understanding of laser plasma chemistry and for elucidating the nature of spectral interferences and matrix effects that may take place in applied spectrochemical analysis.

Flow Injection Analysis↗
PubMed2001

[Simultaneous determination of hydride forming and non-hydride forming elements in human hair by hydride generation-inductively coupled plasma atomic emission spectrometry].

A method for simultaneous determination of both hydride forming and non-hydride forming elements in human hair has also been successful. The influence of HCl concentration, NaBH4 concentration, carrier gas flow rate and rinse time on hydride forming elements intensity, and the effect of between nebulization and hydride-nebulization system on non-hydride forming elements have been studied. The optimum experimental conditions are selected. This method has been applied to the analysis of standard human hair with satisfactory results.

Arsenic↗
PubMed2004

Determination of pipemidic acid based on flow-injection chemiluminescence due to energy transfer from peroxynitrous acid synthesized on-line.

A flow-injection chemiluminescence (CL) method for the determination of pipemidic acid is described. It is based on energy transfer from excited state peroxynitrous acid to pipemidic acid, in which the excited state peroxynitrous acid is synthesized on-line by the mixing of acid hydrogen peroxide with nitrite in a flow system and the CL is from two excited states of pipemidic acid. The proposed method allows the measurement of pipemidic acid over the range of 2.0 x 10(-7)-2.0 x 10(-5) mol l(-1) . The detection limit is 6.3 x 10(-8) mol l(-1), and the relative standard deviation for 2.0 x 10(-6) mol l(-1) pipemidic acid (n = 9) is 0.9%. This method was evaluated by the analysis of pipemidic acid in pharmaceutical preparations.

Energy Transfer↗
PubMed2004

Flow-injection determination of amine contaminants in cyclamate samples based on temperature for controlling selectivity.

This paper describes a flow-injection (FI) method for the simultaneous determination of aniline and cyclohexylamine impurities in cyclamate products. The method consists of the derivatization of amines with 1,2-naphthoquinone-4-sulfonate under selective and non-selective conditions. Here, the selectivity is achieved by working at 20 degree C, at which only aniline reacts, whilst higher temperatures (80 degree C) lead to a non-selective reaction of the two analytes. The FI manifold is composed of two flow cells for the spectrophotometric detection of derivatives at 480 nm. Experimental conditions have been optimized by factorial design and multicriteria making approach. Quantification is accomplished by differential analysis of the analyte contributions in the double peaks generated when the sample reaches cell 1 and cell 2. Results obtained with the proposed method are in satisfactory agreement with those provided by the standard method for the analysis of cyclamate samples.

Aniline Compounds↗
PubMed2003

Simple and inexpensive flow L-glutamate determination using pumpkin tissue.

This work refers to a very easy to implementate flow injection system with potentiometric detection for l-glutamate determination in food samples. The proposed procedure is based on measurement of carbon dioxide produced by decarboxylation of l-glutamate catalyzed by l-glutamate decarboxylase (E.C. 4.1.1.1.5) from Cucurbita maxima (pumpkin). The FI potentiometric system includes an enzymatic reactor with a length of 8 cm and thickness of 5 mm packed with 200 mg of a C. maxima outer layer cut in to small pieces. The proposed procedure allowed l-glutamate determinations in the concentration interval of 10-100 mmol L(-1) for an injected sample volume of 50 microL. A phosphate buffer (0.1 mol L(-1), pH 5.5) solution flowing at 1.4 mL min(-1) was used as the carrier solution in the system. The results obtained in the analysis of food samples revealed a relative error lower than 5% when compared with those provided by the spectrophometric reference procedure. The immobilized reactor retained its initial activity for 21 days. It was possible to measure 40 samples/h with the flow system proposed.

Cucurbita↗
PubMed1998

Flow injection immunoanalysis based on a magnetoimmunosensor system.

A new immunosensor integrated to a flow system has been developed. It is based on magnetic immunoparticles immobilized on a solid-state transducer using a magnetic field. The described technique renews the immunoparticles reproducibly for each analysis allowing a good measurement precision. The developed experimental approach permits the implementation of an automated immunoassay that is quick (analytical cycle < 30 min) and sensitive in the micromolar concentration range. The system was applied to the determination of rabbit immunoglobulin G as an analyte model.

Animals↗
PubMed2006

Ecological role of reindeer summer browsing in the mountain birch (Betula pubescens ssp. czerepanovii) forests: effects on plant defense, litter decomposition, and soil nutrient cycling.

Mammalian herbivores commonly alter the concentrations of secondary compounds in plants and, by this mechanism, have indirect effects on litter decomposition and soil carbon and nutrient cycling. In northernmost Fennoscandia, the subarctic mountain birch (Betula pubescens ssp. czerepanovii) forests are important pasture for the semidomestic reindeer (Rangifer tarandus). In the summer ranges, mountain birches are intensively browsed, whereas in the winter ranges, reindeer feed on ground lichens, and the mountain birches remain intact. We analyzed the effect of summer browsing on the concentrations of secondary substances, litter decomposition, and soil nutrient pools in areas that had been separated as summer or winter ranges for at least 20 years, and we predicted that summer browsing may reduce levels of secondary compounds in the mountain birch and, by this mechanism, have an indirect effect on the decomposition of mountain birch leaf litter and soil nutrient cycling. The effect of browsing on the concentration of secondary substances in the mountain birch leaves varied between different years and management districts, but in some cases, the concentration of condensed tannins was lower in the summer than in the winter ranges. In a reciprocal litter decomposition trial, both litter origin and emplacement significantly affected the litter decomposition rate. Decomposition rates were faster for the litter originating from and placed into the summer range. Soil inorganic nitrogen (N) concentrations were higher in the summer than in the winter ranges, which indicates that reindeer summer browsing may enhance the soil nutrient cycling. There was a tight inverse relationship between soil N and foliar tannin concentrations in the winter range but not in the summer range. This suggests that in these strongly nutrient-limited ecosystems, soil N availability regulates the patterns of resource allocation to condensed tannins in the absence but not in the presence of browsing.

Analysis of Variance↗
PubMed2004

Why the move to microfluidics for protein analysis?

There has been a recent trend towards the miniaturization of analytical tools, but what are the advantages of microfluidic devices and when is their use appropriate? Recent advances in the field of micro-analytical systems can be classified according to instrument performance (which refers here to the desired property of the analytical tool of interest) and two important features specifically related to miniaturisation, namely reduction of the sample volume and the time-to-result. Here we discuss the contribution of these different parameters and aim to highlight the factors of choice in the development and use of microfluidic devices dedicated to protein analysis.

Animals↗
PubMedDate not supplied

Chemiluminescence behaviour of alkaline earth metal ions in the potassium permanganate-fluorescein reaction.

A chemiluminescence (CL) signal was observed when alkaline earth metal ion solution, Mg2+ or Ca2+ or Ba2+, was injected into a reaction mixture of fluorescein and potassium permanganate. A possible CL mechanism is proposed based upon the CL, fluorescence and UV-visible spectra. Furthermore, the feasibility of the application of these reactions to the analysis of these alkaline earth metal ions was evaluated and the analytical parameters of the methods were determined.

Barium↗
PubMed2006

Application of internal universal calibration for determination of fully dissociated species in capillary electrophoresis using indirect UV detection and electrokinetic injection.

Although the electrokinetic injection suffers from quantitation problems arising from mobility and matrix bias, the application of electrokinetic injection and indirect photometric detection may provide a very simple, sensitive and universal determination of fully dissociated components. In this work a survey of the possibilities of quantitative analysis using EK injection with indirect UV detection is given and a simple procedure (internal universal calibration) for accurate quantitative determination of traces using EK injection is proposed. It was shown that the thiosulfate as an internal universal standard (IUS) can be applied for quantitative determination of fully dissociated analytes (e.g. Br(-), Cl(-), NO(2)(-), NO(3)(-), SO(4)(2-), S(2)O(3)(2-)) whose mobilities (migration times) do not differ from the mobilities of monitoring ion (chromate), counter-ion (potassium) and IUS with more than 10%. The proposed calibration procedure provides concentration data, which deviate generally less than 5% extent from the actual true values. The validity and the applicability of the method was studied in the analysis of samples containing different amount of matrix material.

Anions↗