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PubMed1979

Determination of total CO2 in plasma by automated flow-injection analysis.

We describe a procedure for measuring total CO2 in plasma, based on the principles of the flow-injection analysis technique, which makes use of unsegmented fast-flowing reagent streams, as developed by Růziĉka and co-workers. The further methodological design resembles the silicone-rubber membrane technique of Kenny and Cheng. CO2 in the sample is released by reaction with H2SO4. Appropriate amounts of CO2 permeate through the membrane that separates the acid reagent streams and a buffered cresol-red indicator system. The experimental set-up and functioning of this system are described.

Autoanalysis↗
PubMed1994

An in situ electrosynthesized amperometric biosensor based on lactate oxidase immobilized in a poly-o-phenylenediamine film: determination of lactate in serum by flow injection analysis.

The electrochemical immobilization of lactate oxidase in a poly-o-phenylenediamine film permits the one-step and all-chemical construction of a lactate amperometric biosensor. The sensor was prepared in situ i.e. in the flow injection analysis (FIA) system by simply injecting a plug of a solution containing the monomer and the enzyme. At a flow rate of 50 microL/min linearity was observed up to 0.2 mM lactate and detection limits of about 2 microM could be easily achieved. Faradaic interferences caused by ascorbate, urate, cysteine and acetaminophen were sufficiently minimized to permit lactate determination in diluted serum by FIA. Results obtained by FIA-amperometric detection compared well (according to a proper t-test at a 95% confidence level) with those obtained by a standard enzymatic colorimetric assay. At a flow rate of 1 ml/min a sample throughput higher than 70 sample h-1 was achieved. After one week of continuous use in the FIA system a 75% decrease in biosensor sensitivity was observed.

Animals↗
PubMed1997

Simultaneous spectrofluorimetric determination of selenium (IV) and (VI) by flow injection analysis.

A simple, sensitive, highly selective, automatic spectrofluorimetric method for the simultaneous determination of selenium (IV) and (VI) as selenite-selenate by flow injection analysis (FIA) has been developed. The method is based on the selective oxidation of the non-fluorescent reagent 2-(alpha-pyridyl)thioquinaldinamide (PTQA) in acidic solution (1.5-3.0 M H2SO4) by SeIV to give an intensely fluorescent oxidation product (lambda ex =350 nm; lambda em = 500nm). Selenium (VI) is reduced on-line to SeIV, in a reduction coil installed in a photo-reactor, which is then treated with PTQA and the fluorescene due to the sum of SeIV and SeVI is measured; SeVi is determined from the difference in fluorescence values. Various analytical parameters, such as effect of acidity, flow rate, sample size, dispersion coefficient, temperature, reagent concentration and interfering species were studied. The photo-reduction conditions were optimized, with an FIA procedure, for SeVI on the basis of its reduction efficiency. The calibration graphs were rectilinear for 0.1-2.4 micrograms ml-1 of SeVI and 10 ng ml-1-2.2 micrograms ml-1 of SeIV, respectively. The method was applied to the determination of Se in several Standard Reference Materials (alloy, sediments and tea), as well as in some environmental waters (tap and surface water), food samples (flour and egg), a biological sample (human hair), soil sample and in synthetic mixtures. Up to 25 samples per hour can be analysed with an RSD approximately 0.1-2%.

Flow Injection Analysis↗
PubMedDate not supplied

Semiautomatic determination of furanic aldehydes in food and pharmaceutical samples by a stopped-flow injection analysis method.

A kinetic study of the reactions of 5-hydroxymethyl-2-furfuraldehyde and furfural with 2-thiobarbituric acid (TBA) by a stopped-flow flow injection analysis technique has been undertaken. A semiautomatic method for the analytical determination of these furanic aldehydes is proposed on the basis of reaction with TBA. The proposed stopped-flow method was successfully applied to several commercial pharmaceutical preparations and food samples. The procedure is faster than the earlier procedure for determination of these compounds in foods and pharmaceuticals.

Calibration↗
PubMed1990

Use of ionomer membranes to enhance the selectivity of electrode-based biosensors in flow-injection analysis.

The use of ionomer membranes to enhance the selectivity of potentiometric enzyme electrodes in flow-injection measurement arrangements is examined. The ionomer membranes employed are permeable to analyte substrates but relatively impermeable to detectable ions that would normally interfere with the measurement of the substrates if the enzyme electrodes were in direct contact with the sample. As a model system, the selectivity of enzyme electrodes prepared with nonactin-based ammonium-sensitive polymeric membranes is evaluated. In the preferred configuration, a thin hydrophilic anion-exchange membrane is incorporated within a flow-through dialysis unit upstream from the enzyme-electrode detector. As the sample passes through the dialysis unit, neutral or anionic analyte molecules (urea or glutamine) move through the membrane while the permeation of endogenous ammonium ions and other cations in the sample is retarded. A flowing recipient buffer on the other side of the membrane carries the analyte substrate to the enzyme-electrode detector. Enhancements in selectivity for analyte substrates over endogenous ammonium and potassium ions are greater than or equal to 9-fold when compared to enzyme-electrode flow-injection analysis (FIA) systems assembled without the ionomer membrane unit. The analytical utility of the proposed system is demonstrated by the accurate measurements of urea in blood serum and L-glutamine in hybridoma bioreactor media.

Biosensing Techniques↗
PubMed1992

Determination of urinary glucose by a flow injection analysis amperometric biosensor and ion-exchange chromatography.

A practical biosensor system has been developed for the determination of urinary glucose using a flow-injection analysis (FIA) amperometric detector and ion-exchange chromatography. Glucose oxidase was immobilized onto porous aminopropyl glass beads via glutaraldehyde activation to form an immobilized enzyme column. On the basis of its negative charge at pH 5.5, endogenous urate in urine samples was effectively retained by an upstream anion-exchange resin column. The biosensor system possessed a sensitivity of 160 +/- 2.4 RU microM-1 (RU or relative unit is defined as 2.86 microV at the detection output) for glucose with a minimum detection level of 10 microM. When applied for the determination of urinary glucose, the result obtained compared very well with that of the widely accepted hexokinase assay. The immobilized glucose oxidase could be reused for more than 1000 repeated analyses without losing its original activity. The reuse of the acetate anion-exchange column before replacement would be about 25-30 analyses. Acetaminophen and ascorbic acid were also effectively adsorbed by the acetate anion exchanger. The introduction of this type of anion exchanger thus greatly improved the selectivity of the FIA biosensor system and fostered its applicability for the determination of glucose in urine samples.

Adult↗
PubMed1994

The glutamate biosensor and its application to flow injection analysis system.

A micro-enzyme electrode was fabricated by cross-linking L-glutamate oxidase with glutaraldehyde on aminopropyl-platinized platinum wire. A flow injection analysis system with glutamate sensor was used for L-glutamate determination. The peak current is linearly related to the L-glutamate concentration in the range of 0.02-2.0 mM, with good performance, accuracy (CV = 0.4%), fast response (< 60s), and stability (> 20 days). The system was applied to determine the concentration of L-glutamate in a fermentation broth. The recovery rate was in the range of 98.7-107.5%.

Amino Acid Oxidoreductases↗
PubMed1993

Improved flow injection analysis (FIA) method for determining selenium in biological samples, and the effect of captopril administration on selenium levels and glutathione peroxidase activity in rat.

An improved flow injection analysis (FIA) method has been developed for the determination of trace selenium in biological samples, and this method has been applied to investigate the effect of captopril, an antihypertensive drug having a thiol group, on selenium concentrations in the rat blood, liver and urine. After oral administration of captopril, selenium levels in the blood decreased, while those in the liver increased significantly. However, no pronounced effect was observed on the urinary excretion rate. The glutathione peroxidase activities in the blood and the liver were comparable to the changes in the selenium levels.

Administration, Oral↗
PubMed1992

Flow-injection analysis for malondialdehyde in plasma with the thiobarbituric acid reaction.

A simple, precise, and rapid method to measure plasma malondialdehyde (MDA) was developed by use of solvent extraction--flow-injection analysis. The reagent solution, containing thiobarbituric acid (TBA), 5 g/L in 100 mL/L phosphoric acid, and extraction solvent (methylisobutyl ketone, MIBK) were propelled with a double-plunger micropump at a flow rate of 0.3 mL/min, and 20 microL of sample was introduced into the reagent stream. After TBA-MDA reactant was extracted into MIBK, the organic phase was continuously separated by a successive phase-separation system equipped with two phase separators, and the absorbance of the TBA-MDA reactant was measured at 532 nm. This approach resulted in excellent sensitivity, a CV of < 1.5%, a good correlation with the conventional manual method, and a sampling frequency of 7 samples/h, suggesting that this semiautomated method is suitable for measuring plasma MDA.

Animals↗
PubMed1992

Colorimetric determination of free and total cholesterol by flow injection analysis with a fiber optic detector.

A flow injection method for the determination of total and free cholesterol is presented. Cholesterol esterase and cholesterol oxidase are immobilized on aminoalkyl glass beads. The beads are packed into a tubular glass reactor. The cholesterol esters traversing through the esterase reactor are cleaved to cholesterol and fatty acids. The oxidase reactor converts cholesterol to cholest-4-en-3-one and hydrogen peroxide is generated. The sample stream is merged with reagent streams consisting of a peroxidase solution and a solution of 2,2'-azino-bis-(3-ethyl-benzthiazoline-6-sulfonic acid) diammonium salt, and a hydrogen peroxide-dependent color reaction takes place in a short coiled reactor. The signal is monitored by means of fiber optic instrumentation. Cholesterol concentration can be related to the absorption of the oxidized dye form at a wavelength of 425 nm. The working range is 0.5-0.8 mmol l-1, and the sample throughputs are 60 and 30 h-1 for free and total cholesterol, respectively.

Cholesterol↗
PubMed1995

Development of a flow injection analysis (FIA) immunosensor for the detection of Escherichia coli.

A flow injection immunoanalysis (FIA) system has been developed for the detection of Escherichia coli in artificially contaminated food samples. Anti-E. coli antibodies were covalently immobilized onto porous aminopropyl glass beads via glutaraldehyde activation to form an immunoreactor. After adsorption of the cells onto anti-E. coli antibody bound glass beads, 4-methylumbelliferyl-beta-D-glucuronide was injected into the system which was then hydrolyzed by the adsorbed E. coli cells containing beta-D-glucuronidase, an enzyme which is very specific to E. coli and to a few other strains of Shigella. Fluorescent 4-methylumbelliferone released from the enzymatic reaction was then detected by a fluorometer. Owing to the specificity of the antibody towards E. coli, the FIA system was very selective for detection of E. coli whereas Shigella boydii, another GUD-positive bacterium, did not give any response. The FIA system was successfully used for detecting as low as 5 x 10(7) CFU/ml E. coli in less than 30 min and was reusable for at least 300 repeated assays. The immunoreactor yielded reproducible results during 3 months of experimentation if stored overnight at 4 degrees C in carrier buffer containing 0.05 to 0.25% Tween 20.

Escherichia coli↗
PubMedDate not supplied

Determination of sulfur dioxide in wines and beverages by flow injection analysis with reductive amperometric detection and electrolytic cleanup.

A new flow injection method is described for the determination of sulfur dioxide in red and white wines and other beverages. A dual-electrode electrochemical detector eliminates interferences by reduction at an upstream coulometric electrode before reductive detection of sulfur dioxide at the amperometric electrode. The data for free and total sulfur dioxide in wines and other beverages agree well with those obtained by the standard aspiration-oxidation method.

Beverages↗
PubMed1992

Flow injection analysis and in-line biosensors for bioprocess control: a comparison.

Miniaturization will unify the different approaches chosen for the application of biosensors in bioprocess control. The most versatile system, which in our opinion is flow injection analysis will be the method of choice for the introduction of biosensors in bioprocess control. A lot of experience will be gained for the future development of miniaturized total chemical analysis systems.

Biosensing Techniques↗
PubMed1994

Flow injection analysis for glucose using an amperometric enzyme electrode based on lipid-modified glucose oxidase as the detector.

The concentration of glucose is determined by a combination of flow-injection analysis with amperometric enzyme sensor detection. The enzyme sensor is prepared by coating a glassy carbon electrode with a layer of lipid-modified glucose oxidase and Nafion: first, a benzene solution of the modified enzyme is placed on the glassy carbon electrode and dried, then a Nafion solution is placed on the electrode and dried. The sensor-based system exhibited a linear response for glucose concentration up to 10 mM with a sampling rate of 250 sample/h, and is stable for 12 weeks after 2000 glucose injections.

Beverages↗
PubMed1980

Automated multiple flow-injection analysis in clinical chemistry: determination of albumin with bromcresol green.

We describe an adaptation of automated multiple flow-injection analysis instrumentation to an analysis for albumin in serum. The bromcresol green reaction was used to test the utility of the system. The approach yielded albumin results with excellent sensitivity, no measurable carryover, a relative standard deviation of less than 1%, good correlations with published procedures, and no measurable interferences. The simplicity and flexibility of the instrumentation and its performance integrity, as indicated by the analytical results, make this a viable clinical chemical tool.

Bromcresol Green↗
PubMed1992

Use of various types of column reactors for flow-injection analysis.

Two or three different kinds of immobilized enzymes can be aligned in a minireactor so that sequential enzymatic reactions are carried out from upstream to downstream during flow-injection analysis. A lactate oxidase-catalase reactor, used as precolumn for removing pre-existing lactate in serum before the lactose dehydrogenase (LDH) reactions, was useful for the determination of serum LDH activity, which did not require any blank correction. A sequential glutamate dehydrogenase-glutamate oxidase reactor was also useful for a novel chemiluminometric determination of ammonia. On the other hand, a co-immobilized creatininase-creatinase-sarcosine oxidase reactor, in spite of containing creatininase which catalyses the reversible reaction, was the most efficient for the determination of serum creatinine.

Ammonia↗
PubMed1996

A microdialysis fibre based sampler for flow injection analysis: determination of L-lactate in biofluids by an electrochemically synthesised bilayer membrane based biosensor.

A microdialysis fibre based, low volume sampler is described which can be used in flow injection analysis (FIA) when an on-line dilution of the sample and/or removal of high molecular weight interferents is required. This device used in combination with a lactate amperometric biosensor based on lactate oxidase electrochemically immobilised in a bilayer membrane of poly(o-phenylendiamine) and overoxidized poly(pyrrole) permits the extension of the linear range of response up to 10 mM lactate. Combining microdialysis sampling with FIA and amperometric detection at an interference-free and fast-response biosensor, lactate determination in complex media such as serum, milk and yoghurt can be easily achieved with a high sample throughput and no sample pre-treatment.

Animals↗
PubMed1984

Highly sensitive flow injection analysis of glucose and uric acid in serum using an immobilized enzyme column and chemiluminescence.

A method for the flow injection analysis of glucose and uric acid in serum using immobilized enzymes in column form and chemiluminescence detection is described. The method is based on the determination of chemiluminescence formed by the reaction of a luminol-ferricyanide mixture with hydrogen peroxide which is produced by the action of the respective oxidases on glucose and uric acid. Glucose or uric acid in serum were determined with 1 microliter of the sample at a speed of 120 samples/h without carryover and at an assay time of approximately 10 s. The immobilized glucose oxidase column measured only 1.0 X 5 mm, and the immobilized uricase column 1.0 X 20 mm. The present method gave perfect linearity of the data up to 4.0 g glucose per liter or 0.10 g uric acid per liter with satisfactory precision, reproducibility, and accurate reaction recoveries. Furthermore, the present method was hardly affected by ascorbic acid, while the peroxidase-linked colorimetric method is usually influenced significantly by ascorbic acid. Both column reactors showed good operational stability for a 2-month period, during which time they were repeatedly used for analyses over 2000 times. The results on glucose and uric acid correlated satisfactorily with those obtained by other well-established methods.

Blood Glucose↗