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Results for “Flow Injection Analysis”

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At least 1,549 records · Page 86Linked to original sources
PubMed2003

Determination of fluorinated surfactants and their metabolites in sewage sludge samples by liquid chromatography with mass spectrometry and tandem mass spectrometry after pressurised liquid extraction and separation on fluorine-modified reversed-phase sorbents.

An analytical method was elaborated for simultaneous extraction and determination of fluorinated anionic and non-ionic surfactants in sewage sludge. Surfactant compounds were determined by liquid chromatography-mass spectrometry (LC-MS) after Soxhlet extraction, hot steam extraction and pressurised liquid extraction (PLE) using spiked sludge samples. PLE in a multiple-step procedure consisting of sequential use of ethyl acetate-dimethylformamide and methanol-phosphoric acid resulted in the most efficient extraction procedure. Quantitative analyses of the fluorinated anionic perfluorooctanesulfonate (PFOS) and the partly fluorinated non-ionic alkylpolyglycol ether (FAEO) surfactants were performed by selected ion monitoring LC-MS. Electrospray ionisation or atmospheric pressure chemical ionisation in negative or positive mode was performed. Recoveries between 105 and 120% could be reached. No PFOS and non-ionic FAEO surfactants in concentrations higher than 6 or 10 mg kg(-1) dry matter were observed in real environmental samples. Therefore aerobic and anaerobic biodegradation was performed to investigate the fate of fluorinated surfactants reaching wastewaters. Biological wastewater treatment in laboratory scale under aerobic or anaerobic conditions led to an elimination by biodegradation.

Chromatography, Gas↗
PubMed2000

Improved column preparation and performance in capillary electrochromatography.

Problems encountered in capillary electrochromatography, i.e. non-reproducible column manufacture, bubble formation during usage, short column lifetimes and limited choice of packing particles are addressed by the development of fritless or single-frit, internally tapered, segmented and dead-volume free coupled capillary columns. The Van Deemter plots measured demonstrate the performance of these high-quality capillaries which are suitable for capillary electrochromatography as well as for capillary high-performance liquid chromatographic applications.

Benzoates↗
PubMed1997

Liposomes and immunoassays.

Various aspects of the application of liposomes as a label in immunoassays are reviewed. Methods for the preparation of liposomes, from the basic film method to the more advanced dehydration-rehydration method, are discussed. Furthermore, the markers used in liposome labels, as well as the methods to conjugate liposomes to antigens or antibodies, are summarized. Liposome immunoassays are applied as homogeneous or heterogeneous assays. Homogeneous assays often rely on the lytic activity of complement on antibody-associated liposomes. Another group of homogeneous assays utilizes the inhibitory action of antibodies on the activity of conjugates of mellitin (a bee venom protein) with a hapten. Free mellitin conjugates are able to lyse liposomes effectively. Heterogeneous liposome immunoassays, performed either competitively or non-competitively, resemble more closely standard enzyme linked immunosorbent assays, with the enzyme being replaced by a liposome label. Washing steps are used to separate antigen-specifically bound liposomes from unbound liposomes. All bound liposomes are lysed with a detergent, giving an instantaneous amplification. Flow-injection liposome immunoassays and liposome immunosensors are also described as examples of other possible immunoassay formats.

Biosensing Techniques↗
PubMed1997

Design of non-competitive flow injection enzyme immunoassays for determination of haptens: application to digoxigenin.

A theoretical model immunoradiometric assay (IRMA) was adapted to provide a non-competitive flow injection enzyme immunoassay for haptens and used as a guide in studying the effects of different parameters on the sensitivity, precision and dynamic range of the assay. As well as the concentration of the antibody-enzyme conjugate, the affinity constant, the run time through the affinity column, the homogeneity of the antibody population and purity of the antibody-enzyme conjugate were all shown to be important parameters in the optimisation of the assay. The findings were used to design an optimised enzyme flow injection immunoassay for the model compound digoxigenin in standard solutions. A linear calibration curve was established in the range 0.38-7.7 fmol of digoxigenin, resulting in a precision of 14.8% RSD at 1 fmol and 3.7% RSD at 7.7 fmol. Antibody fragments reacting with digoxigenin and labelled with alkaline phosphatase, (Fab-AP) were used to convert 4-methyl umbelliferyl phosphate to a fluorescent product measured downstream. The sample throughput was 15 h-1 and over 60 injections were possible before regenerating the affinity column.

Chromatography, Affinity↗
PubMed1997

Identification of a new diarrhoetic toxin in shellfish using liquid chromatography with fluorimetric and mass spectrometric detection.

A new toxin, dinophysistoxin-2B (DTX-2B) was isolated from Irish mussels using silica chromatography, gel permeation, octadecylsilane solid-phase extraction and repeated preparative high-performance liquid chromatography (HPLC). Dinophysistoxin-2 (DTX-2) was also isolated from shellfish using the same procedures. The separation of these toxins in chromatographic fractions was monitored using fluorimetric HPLC following derivatization with 9-anthrylmethyldiazomethane or 1-bromoacetylpyrene. Flow-injection analysis-mass spectrometry (FIA-MS) with an atmospheric pressure ionization (API) and an ionspray (ISP) interface showed a mass spectrum dominated by the protonated molecule, [M+H]+, at m/z 805 for DTX-2B, thus indicating that this new toxin has the same mol.wt as okadaic acid and DTX-2. The low-energy fragment ion spectrum, as produced in FIA-MS experiments by up-front collision-induced dissociation of the protonated molecule of DTX-2B, showed fragment ions corresponding to successive losses of water molecules from the [M+H]+ ion. This low collision energy fragmentation pattern is typical of marine polyether toxins such as okadaic acid, DTX-2 and DTX-1. These results provide strong evidence that DTX-2B is another okadaic acid isomer.

Animals↗
PubMed2002

Literature survey of on-line spectroscopic methods for lead determination in environmental solid samples.

A review is presented where are shown the advantages involved in the use of flow injection (FI) analysis for the determination of lead in environmental solid samples by spectroscopic detectors. The FI methods proposed for the determination of lead in these samples are described and compared according to the detection technique used. Analytical data of interest and interferences are discussed for each technique.

Environmental Monitoring↗
PubMed1998

Following the folding of RNA with time-resolved synchrotron X-ray footprinting.

The rapid mixing synchrotron X-ray footprinting technique described in this article allows nucleic acid folding and ligand binding reactions to be followed on a millisecond time resolution with single nucleotide resolution. In principle, the change in .OH protection of every nucleotide in a nucleic acid hundreds of nucleotides long can be monitored separately. In addition, a wide range of solution conditions are compatible with the radiolytic generation of .OH. These characteristics of synchrotron X-ray footprinting create opportunities for conducting thermodynamic and kinetic studies of nucleic acids that are both comprehensive and detailed. Kinetic footprinting studies of a number of systems have been initiated by the Center for Synchrotron Biosciences using this technique.

Flow Injection Analysis↗
PubMedDate not supplied

Development of enantioselective chemiluminescence flow- and sequential-injection immunoassays for alpha-amino acids.

The development of an enantioselective flow-through chemiluminescence immunosensor for amino acids is described. The approach is based on a competitive assay using enantioselective antibodies. Two different instrumental approaches, a flow-injection (FIA) and a sequential-injection system (SIA), are used. Compared to the flow-injection technique, the sequential injection-mode showed better repeatability. Both systems use an immunoreactor consisting of a flow cell packed with immobilized haptens. The haptens (4-amino-L- or D-phenylalanine) are immobilized onto a hydroxysuccinimide-activated polymer (Affi-prep 10) via a tyramine spacer. Stereoselective antibodies, raised against 4-amino-L- or D-phenylalanine, are labeled with an acridinium ester. Stereoselective inhibition of binding of the acridinum-labeled antibodies to the immobilized hapten by amino acids takes place. Chiral recognition was observed not only for the hapten molecule but also for a series of different amino acids. One assay cycle including regeneration takes 6:30 min in the FIA mode and 4:40 min in the SIA mode. Using D-phenylalanine as a sample, the detection limit was found to be 6.13 pmol/ml (1.01 ng/ml) for the flow-injection immunoassay (FIIA) and 1.76 pmol/ml (0.29 ng/ml ) for the sequential-injection immunoassay (SIIA) which can be lowered to 0.22 pmol/ml (0.036 ng/ml) or 0.064 pmol/ml (0.01 ng/ml) by using a stopped flow system. The intra-assay repeatability was found to be about 5% RSD and the inter-assay repeatability below 6% (within 3 days).

Acridines↗
PubMed2003

Flow-based amperometric detection of dopamine in an immobilized cell reactor.

A protocol is described for immobilizing PC 12 cells on to the lumen of fused silica microbore tubing having an inside diameter of 250 microm and coated with a thin layer of poly-L-lysine. Optimization studies of the immobilization procedure indicated that a 50 microg ml(-1) solution of poly-L-lysine was the best material for cell adhesion to the fused silica tubing. In addition, it was found that the cells become attached to the poly-L-lysine in approximately 2 h, after which they could be maintained inside of the tubing for a period up to 5 days. Importantly, the immobilized cells ability to release neurotransmitters was evident by measuring the Ca(2+)-induced release of dopamine with an in column amperometric detection scheme involving a Nafion modified platinum ultramicroelectrode.

Animals↗
PubMed2003

A picoliter 'fountain-pen' using co-axial dual pipettes.

A double pipette system for local, controlled drug infusion is presented. Two concentric pipettes can be manipulated separately and pressurized independently by a designated double holder. The inner pipette is loaded with the desirable solution (drug), and functions as a source, while the outer one is a sink. This gives a flow of the solution between the two pipettes that protrudes only a small distance into the surrounding fluid and does not diffuse away. Time resolution of the infusion is highly controllable, and oscillatory flow can be generated. Three implementations of the double pipette system are demonstrated. We show that local application of neurotransmitters in neuronal networks is an efficient way of stimulating activity in the network. We then present a wet micro lithography technique using topical application of proteins onto the substrate. Finally, we show that we can localize a given drug on a small targeted part of a cell.

Animals↗
PubMed2003

Lysine synthesis control in Corynebacterium glutamicum RC 115 in mixed substrate (glucose-acetate) medium.

The effect of acetate as a glucose co-substrate on growth, lysine synthesis and experimental lysine yield from carbon substrates by Corynebacterium glutamicum RC 115 was investigated. It was found that low amounts of acetate, injected with a glucose-acetate pulse into the steady-state continuous culture in bioreactor, caused a slight decrease in the specific rates of glucose uptake and bacterial growth, but a significant increase in the cell specific rate of lysine synthesis and an increase in lysine yield. In contrast, acetate injected in high amounts was followed by a drastic decrease in the values of these parameters. A strong increase in experimental lysine yield under the latter conditions was reached in the response to pyruvate addition. Therefore it was shown that acetate in low concentrations can be used as a glucose co-substrate to increase the cell specific rate of lysine synthesis and lysine yield by C. glutamicum RC 115. Pyruvate supplementation was found as a promising method to enhance lysine synthesis by bacterial cells grown in glucose-acetate media with an increased concentration of acetate.

Acetates↗
PubMed2001

An electrochemical multienzymatic biosensor for determination of cholesterol.

This paper describes an electrochemical biosensor for free cholesterol monitoring. The sensor is a multienzymatic electrodic system in which horseradish peroxidase and cholesterol oxidase are simultaneously immobilized within a polymeric film, on the surface of a pyrolitic graphite electrode. From voltammetric and amperometric (flow-injection) data obtained, the efficiency, reproducibility and stability of the system are discussed. Results obtained, of interest for basic and applied biochemistry, represent a first step for construction of a mediator-free biosensor with potentialities for a successful application in the biosensor area.

Biosensing Techniques↗
PubMed2000

Rapid simultaneous determination of glucagon and insulin by capillary electrophoresis immunoassays.

A rapid capillary electrophoresis (CE) with laser-induced fluorescence (LIF) competitive immunoassay has been developed for the determination of glucagon in biological mixtures. In the assay, fluorescein-conjugated glucagon is mixed with the sample followed by addition of anti-glucagon. Free and antibody-bound, tagged glucagon could be separated in 3 s using CE to obtain quantitative determination of glucagon with a concentration detection limit of 760 pM. The assay was combined with a previously developed competitive immunoassay for insulin to produce a simultaneous immunoassay for both peptides. The method was used to determine glucagon content of islets of Langerhans.

Animals↗
PubMed2001

High-throughput fluorescence flow-injection topoisomerase II inhibition assay.

A high-throughput fluorescence flow-injection assay is described, suitable for determining the catalytic inhibition of DNA topoisomerase II. The method, which separates high molecular mass trypanosome kinetoplast DNA from its decatenated product by centrifugation, should be useful for the rapid and accurate screening of potential anticancer topoisomerase II inhibitors and the determination of their inhibition constants. Advantages of the flow-injection method over agarose gel electrophoresis and radioactive centrifugation assays are that it is faster, more sensitive, highly linear in its response to product formation, and does not require the production of radioactive trypanosome kinetoplast DNA substrate.

Animals↗
PubMed1998

Gradient reversed-phase liquid chromatography coupled on-line to receptor-affinity detection based on the urokinase receptor.

A postcolumn receptor-affinity detection (RAD) was developed for the detection of urokinase and cross-reactive compounds. The analytical method consisted of gradient reversed-phase HPLC coupled on-line to a RAD system based on fluorescein-labelled urokinase receptor (fluorescein-uPAR) as reagent. Fluorescein-uPAR was added continuously to the HPLC effluent to react with analytes eluting from the LC column. Unreacted fluorescein-uPAR was removed by a short affinity column packed with an immobilised urokinase support. The analyte-bound fluorescein-uPAR fraction passes the affinity column unretained and was detected downstream by means of a fluorescence detector. An absolute detection limit of 40 fmol urokinase was obtained in the flow injection mode. In the gradient HPLC-RAD system a detection limit of 40 nM (20-microl injection, absolute amount, 800 fmol) was obtained. The present method allowed the identification of active breakdown products of urokinase both in standard samples and biological matrices.

Chromatography, Affinity↗