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At least 163 records · Page 9Linked to original sources
PubMed2000

Mid-infrared quantum cascade lasers for flow injection analysis

A Fabry-Perot quantum cascade laser (QCL) was used as a powerful light source for mid infrared (MIR) detection in flow injection analysis. The QCL lased at several wavelengths close to each other within a few wavenumbers (990-1010 cm-1), hence fitting well to the broad absorption bands of molecules in liquid phase. As compared with that of a state-of-the-art Fourier transform spectrometer, the signal-to-noise ratio could be improved by a factor of 50. Additionally, by using a QCL as the light source, optical path lengths of more than 100 microns could be used even in aqueous matrixes which reduced the danger of cell clogging. In the example shown here phosphate was determined in Diet Coke samples. The flow injection system used allowed the measurement of the sample at two pH values (5 and 13) at which the analyte was present as H2PO4- and PO4(3-), respectively. As the analytical readout the difference in IR absorption of H2PO4- and PO4(3-) at the laser wavelengths was taken. The FIA-QCL measurements were corroborated by ion chromatography which was used as a reference method.

Journal Article↗
PubMed2001

Measuring the CO2 flux at the air/water interface in lakes using flow injection analysis.

The carbon dioxide flux at the air/water interface in lakes was calculated after the determination of H2CO3* (free CO2) and atmospheric CO2 using flow injection analysis (FIA) coupled to a conductometric detector. The method is based on the diffusion of CO2 through a hydrophobic membrane into a flow of deionized water, generating a gradient of conductivity proportional to the concentration of CO2 in the sample. Using one experimental set-up, the speciation of the inorganic carbon (H2CO3* and dissolved inorganic carbon) was accomplished by simply adjusting the sample pH. The determination of CO2 in the atmosphere was carried out by direct injection of the gaseous samples. The FIA apparatus was taken into the field and CO2 fluxes were evaluated in several Brazilian lakes. In these lakes, representing different eutrophic stages, the CO2 flux varied from -242 (invasive) up to 3227 (evasive) mumol CO2 m-2 h-1.

Air Pollution↗
PubMed2000

Flow injection analysis of cholic acids in pharmaceutical preparations using a polymeric membrane ISE as detector.

The results reported in this paper regard the setting up of a polymeric membrane ISE that is selective for cholic acids (CA) and able to work in a flow system, especially in flow injection analysis (FIA), based on the exchanger (tetrakisdecylammoniumcholate, TDACh), which has proved effective, is of very simple but suitable structure and is above all easy to synthesise starting from commercially available chemicals. A complete analytical characterisation of the sensor was performed working both in batch conditions and in FIA, using in the latter case a 'wall jet' type of flow cell. The response toward different bile acid sodium salts such as the CA, deoxycholic (DCA), chenodeoxycholic (CDCA), ursodeoxycholic (UDCA), taurocholic (TCA) sodium salts was checked. The application to the analysis of different commercial drugs by FIA was also performed to determine the UDCA or CDCA acid content of several pharmaceutical formulations. Lastly, a preliminary study is presented concerning the use of the investigated electrochemical sensor as high performance liquid chromatography (HPLC) detector.

Cholic Acids↗
PubMed1995

On-line control of an immobilized hybridoma culture with multi-channel flow injection analysis.

An immobilized hybridoma cell line was cultivated at controlled glucose and glutamine concentrations. On-line analysis of the substrates was carried out with a multi-channel flow injection analysis system. The analysis system also determined on-line the lactate and ammonium concentration. The substrate concentrations were controlled using an adaptive-control strategy. This strategy consisted of the estimation of the real-time concentrations and volumetric substrate consumption rates by an Extended Kalman Filter, and a minimum variance controller, which used the estimated parameters to set the feed rates of the substrates. The closed-loop control was used to start-up two cultures with either glucose or glutamine as control-substrate for the medium feed rate. The controller kept the concentration of the control-substrate constant by enhancing the medium feed rate simultaneously to the increasing volumetric consumption rate of the substrate. When glutamine was used as control-substrate, the glucose concentration remained relatively constant, whereas the glutamine concentration decreased during the start-up at a constant glucose concentration. This indicates that glutamine is consumed faster than glucose and will be a better control-substrate to avoid limitation during the start-up of a culture with the applied hybridoma cell line. During the colonization of the microcarriers, the yield of ammonium on glutamine decreased from 0.80 to 0.55 (mol mol-1), indicating a change in the glutamine metabolism. The yield of lactate on glucose stayed constant for both experiments. During long-term culture of more than 800 h, the controller kept both the glucose and glutamine concentrations constant at perfusion rates between 0.50 h-1 and 0.15 h-1. The medium, glucose and glutamine feed rate were independently controlled. Both the specific glutamine and glucose consumption rates remained constant for all perfusion rates, which was probably as a result of the constant concentrations. The specific monoclonal antibody production rate decreased with the perfusion rate decreasing from 0.40 h-1 to 0.20 h-1. The immobilized-cell concentration decreased only at the lowest perfusion rate. Both effects could not be explained directly by the increasing ammonium and lactate concentrations nor by the decreasing amino-acid concentrations.

Animals↗
PubMed1999

Characterisation of a thermophilic L-glutamate dehydrogenase biosensor for amperometric determination of L-glutamate by flow injection analysis.

Carbon paste wax electrodes incorporating thermophilic L-glutamate dehydrogenase, NADP and a polymeric toluidine blue O (poly-TBO) mediator have been characterised for the amperometric determination of L-glutamate at 313-318 K in a flow injection analysis (FIA) system. The biosensors exhibit good sensitivity, mechanical stability and reproducibilty, unlike carbon paste- or carbon wax-based electrodes under the same conditions. The carbon paste wax electrode responds linearly to L-glutamate up to 40 mM, the detection limit is 0.3 mM and the RSD (n = 10) for 5 mM L-glutamate was 7.6%. The response to some potential interferents has been quantified. Addition of finely ground hexaammineruthenium (III) trichloride ([Ru(NH3)6]Cl3) to the carbon paste wax electrodes decreases the FIA peak width and increases the peak current. The metal complex appears to accelerate the rate of oxidation of NAD(P)H by poly-TBO.

Biosensing Techniques↗
PubMed2000

Electrochemiluminescent metallopolymer coatings: combined light and current detection in flow injection analysis.

The application of thin films of the metallopolymer [Ru(bpy)2PVP10]2+ for the electrochemiluminescent (ECL) detection of oxalate in a flow injection analysis system is reported, where bpy is 2,2'-bipyridyl and PVP is poly(4-vinylpyridine). Immobilization of the ECL reagent means that it can be regenerated in situ, eliminating the need to constantly deliver it to the reaction zone. Electrochemically generated Ru3+ reacts with the analyte to form the excited-state [Ru2+]*, which luminesces at 610 nm. The reaction is optimal at low pH, where the layer is swollen and homogeneous charge transport through the layer is more facile. Unlike traditional approaches, we simultaneously monitor both the amperometric and luminescent response of the modified electrode. The precision of both signals is similar at approximately 2% (n = 10). However, the ECL response has a larger dynamic range extending from the low-micromolar to high-millimolar range and a lower limit of detection, approximately 0.2 microM or 4 pmol of oxalate injected. The ECL approach displays excellent selectivity for oxalate over a wide range of potential interferences including oxygen, amines, iron sulfate, ammonium nitrate, urea, and glucose. Ascorbic acid represents the most significant ECL interference. However, the signal observed for a 1 mM solution of ascorbic acid is still only 2.6% of the response observed for the injection of a similar concentration of oxalate.

Journal Article↗
PubMed1988

Immobilization of linamarase and its use in the determination of bound cyanide in cassava using flow injection analysis.

Extracts from the tubers (cortex and parenchyma) and leaves of Manihot esculenta Crantz (cassava) were analyzed for their releasable cyanide content using flow injection analysis incorporating an immobilized linamarase bioreactor. Linamarase was immobilized under very mild conditions to an activated 2-fluoro-N-methylpyridinium Fractogel support. The released cyanide, which was monitored spectrophotometrically at 525 nm using an alkaline picrate reagent, was found to be highest in the cortex and lowest in the parenchyma.

Calibration↗
PubMed1992

[Construction and application of all-solid-state aconitine electrochemical detector in flow injection analysis].

A new kind of all-solid-state electrochemical detector for very toxic alkaloids such as aconitine, mesaconitine and hypaconitine has been studied. It exhibits Nernstian response for these alkaloids with a slope of 56 mV/decade over the concentration range of 3 x 10(-5)-1 x 10(-2) mol/L at pH 2-7 under the flow condition. Direct potentiometry for the determination of aconitine in Aconitum kusnezoffii Reichb., Aconitum carmichaeli Debx. and Xiaohuoluo Wan showed average recoveries of 98.5, 98.3 and 96.8% and relative standard deviations of 1.8, 2.4 and 3.5%, respectively. It can be used for the determination of very toxic alkaloids in the above mentioned samples by flow injection analysis. It also can be used for the study of the hydrolytic kinetics of aconitine.

Aconitine↗
PubMed1994

Determination of L-glutamate using flow injection analysis with immobilized L-glutamate oxidase reactor.

L-Glutamate oxidase (GOD) and horseradish peroxidase (HRP) were covalently coupled on alkylamine pretreated controlled pore glass (CPG) by means of glutaraldehyde. The immobilized enzymes were packed into a teflon tube and used in flow injection analysis (FIA) system for L-glutamate determination. A good linearity range was obtained at 0.1-2.0 mM, and the coefficient of variation was 0.7% (n = 8). More than 80 samples were measured within an hour. The stability of the immobilized GOD reactor was good, retaining 50% of its initial activity after 4 months storage in buffer at 4 degrees C. When the concentration of L-glutamate remained lower than 2.5 mM, the determination of L-glutamate in this system was not affected by pH and temperature within the range of 6.0-8.0 and 20-35 degrees C, respectively. The system was applied to determine L-glutamate in broth samples during L-glutamate fermentation and good correlations were achieved between results obtained with the FIA system, L-glutamate oxidase kit and Warburg's method.

Amino Acid Oxidoreductases↗
PubMed1990

Flow injection analysis and real-time detection of RNA bases by surface-enhanced Raman spectroscopy.

Surface-enhanced Raman scattering (SERS) spectroscopy has been successfully interfaced with a flow injection analysis system to detect RNA bases in real time. Four of the major base components of RNA, uracil, cytosine, adenine, and guanine, were introduced into the flow injection system and were mixed with a Ag sol prior to SERS measurements. Several experimental parameters including pH, temperature, flow rate, and tubing materials were examined, and their impact on the SERS spectra is presented here. The feasibility of interfacing flow injection based SERS detection methods with liquid or high-performance liquid chromatography for the detection of individual components in a complex mixture is also assessed.

Chromatography, High Pressure Liquid↗
PubMed1999

Flow injection analysis of mercury(II) in pharmaceuticals based on enzyme inhibition and biosensor detection.

An enzymatic amperometric procedure for measurement of mercury(II) in pharmaceuticals, based on the inhibition of invertase and on a glucose electrode was studied. Analytical parameters for measurements in batch and flow injection analysis (FIA) have been optimised. Mercury(II) was detected in the 10-60 ppb range with RSD < or =2%. A sample throughput of 6 h(-1) for batch and 15 h(-1) for FIA was obtained. The total mercury(II) from thimerosal (thiomersal, sodium ethylmercurithiosalicylate) in eye-drop samples was measured with the amperometric procedure after oxidative cleavage treatment. Results for both batch and FIA procedures correlated well with atomic absorbtion spectroscopy (AAS) data.

Biosensing Techniques↗
PubMed1994

Automated determination of antibody oxidation using flow injection analysis.

The oxidation of antibody carbohydrate residues is a common approach used for site-specific antibody immobilization or modification. In this study a flow injection analysis system (FIA) was developed for monitoring antibody oxidation. Antibodies were oxidized with periodate and the resulting aldehyde groups were labeled with Lucifer yellow CH (LyCH). The labeled antibodies were then injected onto an FIA system where the amount of LyCH label was determined by absorbance measurements at 428 nm and the amount of antibody was determined using an on-line bicinchoninic acid protein assay. The analysis time was 2 min per 20 microliters sample injection. The limits of detection for rabbit immunoglobulin G (IgG) and LyCH were 1 x 10(-8) and 4 x 10(-7) M, respectively. The dynamic ranges for IgG and LyCH extended to 2 x 10(-5) and 7 x 10(-3) M. The within-run precision was +/- 5% or less for both analytes. Studies with known LyCH/antibody mixtures indicated that the FIA system had greater accuracy than manual methods at high LyCH levels. One specific application studied for this system was its use in monitoring the time course of periodate-antibody oxidation.

Animals↗
PubMed1991

Determination of proteolytic enzymes by flow-injection analysis.

Quantitation of proteolytic enzymes using N-succinyl-L-Ala-L-Ala-L-Pro-L-Phe-p-nitroanilide has been adapted to flow-injection analysis. This procedure has been developed using two different proteases: subtilisin and chymotrypsin. For both enzymes the influence of substrate concentration on spectrophotometric response has been studied. The assay is based on the merging zones technique combined with a washing step. Results are obtained in less than 15 s and samples may be run at a rate of 90/h with good reproducibility. A linear relation between peak heights and enzyme concentrations was observed for 0-0.15 Anson unit/liter of subtilisin and for 0-30 mg/liter of a commercial preparation of chymotrypsin. The method requires only small sample volumes, and the consumption of the chromogenic substrate is reduced to a minimum by using intermittent pumping.

Amino Acid Sequence↗
PubMed1995

The use of differential measurements with a glucose biosensor for interference compensation during glucose determinations by flow injection analysis.

A novel detection system for the determination of glucose in the presence of clinically important interferents, based on the use of dual sensors and flow-injection analysis (FIA), is described. The normalisation methodology involves measurement of the interference signal at a reference sensor; this signal can then be subtracted from the glucose sensor signal (post-run) to give a corrected measurement of the glucose concentration. The detection system consists of a thin layer with dual glassy carbon working electrodes. One electrode was surface modified to act as a glucose biosensor by immobilisation of glucose oxidase (GOx) (from Aspergillus niger) with 1% glutaraldehyde and bovine serum albumin. The second electrode (glucose oxidase omitted) was utilised to measure the interference signal responding only to electroactive species present in the injected sample. A computer controlled multichannel potentiostat was used for potential application and current monitoring duties. The sensor responses were saved in ASCII format to facilitate post-run analysis in Microsoft Excel. Cyclic voltammetry (CV) was utilised to investigate the manner in which the interference signal contributed to the total signal obtained at the biosensor in the presence of glucose. The kinetics parameters Imax and the apparent Michaelis-Menten constant, K'm, were calculated for the sensor operating under flow-injection conditions.

Acetaminophen↗
PubMed2001

Application of automated flow injection analysis to drug liberations studies with the Franz diffusion cell.

The flow-injection method with sensitive fluorimetric detection is used to monitor the liberation profiles of a topical dermatological formulation containing the model compound salicylic acid. The connection of a standard Franz diffusion cell with the automated flow-injection system enables an acquisition of multi-point liberation data in a form of series of fluorescence peaks in a short time. Examples of liberation profiles for a topical dermatological formulation containing salicylic acid are shown.

Autoanalysis↗
PubMed1993

Flow injection analysis of formaldehyde leached from denture-base acrylic resins.

Formaldehyde is responsible for allergic inflammation in acrylic denture wearers and the quantitation of formaldehyde is necessary to study its leaching from denture-base materials. Flow injection analysis was developed to quantify the formaldehyde leached from acrylic resins. Different resins were immersed in aqueous solvents at 37 degrees C and the immersion solutions were directly injected into the flow system, in which formaldehyde was converted on-line to a fluorescent derivative and its fluorescence was detected. Under the optimized conditions, the leached formaldehyde could be quantified in a short time (within 4 min) with high sensitivity (pmol levels per injection) and high specificity (no fluorescent response to the other leachables). In leaching experiments, significant amounts of formaldehyde were leached from autopolymerized resins, but not from heat- and microwave-polymerized resins.

Acrylic Resins↗
PubMed1995

A chemiluminescence-flow injection analysis of serum 3-hydroxybutyrate using a bioreactor consisting of 3-hydroxybutyrate dehydrogenase and NADH oxidase.

We describe a simple method for the highly sensitive chemiluminescence--flow injection analysis of 3-hydroxybutyrate in serum using a bioreactor column consisting of the two immobilized enzymes, 3-hydroxybutyrate dehydrogenase and NADH oxidase. The method was based on measuring the level of chemiluminescence formed by the reaction of a luminol-hexacyanoferrate mixture with hydrogen peroxide. The hydrogen peroxide was produced by the NADH oxidase reaction from NADH which was formed in the conversion of 3-hydroxybutyrate to acetoacetate by the 3-hydroxybutyrate dehydrogenase reaction. Among three immobilized enzyme columns, a coimmobilized, small 3-hydroxybutyrate dehydrogenase/NADH oxidase bioreactor alone (2 x 20 mm i.d.) readily hydrolyzed all of the injected 3-hydroxybutyrate into acetoacetate, although 3-hydroxybutyrate dehydrogenase catalyzed the reversible reaction. The present method generated linearity of the data up to 1.5 mM 3-hydroxybutyrate with satisfactory precision, reproducibility, and accurate reaction recoveries. The results from 3-hydroxybutyrate correlated satisfactorily with those obtained by other well-established methods. The coimmobilized 3-hydroxybutyrate dehydrogenase/NADH oxidase reactor unit showed good operational stability over a 5-week period, during which it was repeatedly used for 1500 analyses.

3-Hydroxybutyric Acid↗
PubMed2000

Flow injection analysis of fluoride: optimization of experimental conditions and non-linear calibration using artificial neural networks.

This paper deals with the application of artificial neural networks (ANNs) to two common problems in spectroscopy: optimization of experimental conditions and non-linear calibration of the result, with particular reference to the determination of fluoride by flow injection analysis (FIA). The FIA system was based on the formation of a blue ternary complex between zirconium(IV), p-methyldibromoarsenazo and F- with the maximum absorption wavelength at 635 nm. First, optimization in terms of sensitivity and sampling rate was carried out by using jointly a central composite design and ANNs, and a neural network with a 3-7-1 structure was confirmed to be able to provide the maximum performance. Second, the relationship between the concentration of fluoride and its absorbance was modeled by ANNs. In this process, cross-validation and leave-k-out were used. The results showed that good prediction was attained in the 1-4-1 neural net. The trained networks proved to be very powerful in both applications. The proposed method was successfully applied to the determination of free fluoride in tea and toothpaste with recoveries between 96 and 101%.

Calibration↗