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PubMed2001

o-Dianisidine: a new reagent for selective spectrophotometric, flow injection determination of chlorine.

A flow injection analysis (FIA) procedure for the determination of free chlorine in industrial formulations and water samples is proposed. The manifold is provided with a gas-diffusion unit which permits the removal of interfering species and also the preconcentration of chlorine. The determination of chlorine is performed on the basis of the oxidation by o-dianisidine as a chromogenic reagent to a coloured product which can be monitored at 445 nm. The method (for a preconcentration step of 60 s) is linear over the range 0.04-1.00 mg l(-1) of chlorine, the limit of detection is 0.04 mg l(-1), the reproducibility of the procedure (as RSD of the slope) is 3.7% for a series of four independent calibrations, the precision (as RSD of a series of 30 continuous FIA peaks of 0.56 mg l(-1) of chlorine) is 1.4% and the sample throughput is 40 h(-1). A detailed comparative study of the analytical characteristics of a single mono-channel reverse FIA assembly and the same system but provided with a Fluoropore membrane filter of 0.5 microm pore size was performed to check the advantages of the new approach in terms of sensitivity, selectivity and limit of detection.

Chlorine↗
PubMedDate not supplied

Flow injection system with chemiluminometric detection for enzymatic determination of ascorbic acid.

A simple, selective and rapid method for determination of ascorbic acid from fruit juices was developed by combining a flow injection analysis (FIA) system with a chemiluminometric detector and a reactor with L-ascorbate oxidase immobilized on controlled pore glass. It was found that some reducing agents (eg ascorbic acid and mercaptoacetic acid) give chemiluminescence with luminol in the presence of hexacyanoferrate (III) in an alkaline solution. We used this new type of chemiluminescent reaction for the enzymatic determination of ascorbic acid. The background substraction method was used in order to avoid interference during ascorbic acid determination. Accordingly, two chemiluminometric signals were registered for each determination, one signal corresponding to the sample that passed through the enzymatic reactor that decomposed the ascorbic acid completely, and the second signal corresponding to the sample that does not pass through the reactor. The difference between the two signals corresponds to ascorbic acid from the sample. The linear range of the method was 10-1000 micromol/L of ascorbic acid and the detection limit was 5 micromol/L The throughput was four samples/h and RSD 3.13% (n = 10). This method was applied for determination of ascorbic in fruit juices. The results were compared with those found by the reference method, based on titrimetric determination with 2,6-dichlorophenolindophenol, and the concordance was excellent.

Ascorbate Oxidase↗
PubMed2005

PVC membrane ion-selective electrodes for the determination of Hyoscyamine in pure solution and in pharmaceutical preparations under batch and flow modes.

New PVC membrane electrodes selective for the determination of hyoscyamine ion (Hy(+)) based on hyoscyamine tetraphenylborate (Hy-TPB) or hyoscyamine phosphotungstate (Hy-PT) ion-exchangers as electroactive materials are described. The electrodes show a linear response for Hy(+) over the concentration range of 1.00 x 10(-5) to 1.26 x 10(-2) mol L(-1) and 1.00 x 10(-4) to 1.00 x 10(-2) mol L(-1) in case of Hy-TPB electrode applying batch and flow injection analysis (FIA), respectively, and 1.00 x 10(-5) to 4.52 x 10(-3) mol L(-1) and 6.31 x 10(-5) to 1.00 x 10(-2) mol L(-1) in case of Hy-PT electrode for batch and FIA, respectively. The lower detection limits are 3.90 x 10(-6) and 4.51 x 10(-6) at 25 degrees C for Hy-TPB and Hy-PT electrodes, respectively. The electrodes posses near Nernstian slopes of 56.5 and 57.8 mV/decade for Hy-TPB and Hy-PT electrodes, respectively, and a fast potential response of < or =20 s which is almost constant over a pH range of 3-10. Selectivity coefficient data for some common inorganic cations, sugars, amino acids and the components, other than hyoscyamine, of the mixed drugs investigated show negligible interference. The electrodes have been applied to the potentiometric determination of hyoscyamine in pure solution and in pharmaceutical preparations under batch and FIA conditions and as end point indicator electrode for the determination of hyoscyanine using potentiometric titration. For the concentrations (1.08 x 10(-5) mol L(-1) to 3.16 x 10(-3) mol L(-1)) an average recovery of 99.95% with relative standard deviation of 0.63% has been achieved. The effect of temperature on the electrodes was also studied.

Atropine↗
PubMed1999

An enzyme thermistor-based assay for total and free cholesterol.

A method to evaluate the free (FC) and total cholesterol (TC) in human serum, bile and gallstone extract using an enzyme thermistor (ET)-based flow injection analysis (FIA) is presented. The cholesterol in high-density (HDL-C) and low density lipoprotein (LDL-C) have also been evaluated. A heparin functionalized Sepharose column was employed for the isolation of HDL and LDL fractions from serum. The estimation of cholesterol and its esters was based on their reaction with cholesterol oxidase (CO), cholesterol esterase (CE) and catalase (CAT). Three different enzyme columns, i.e. co-immobilized CO/CAT (column A), only CE (column B) and co-immobilized CO/CE/CAT (column C) were prepared by cross-linking the enzymes on glass beads using glutaraldehyde. Column A was used for estimating FC and column C was used for estimating total cholesterol (cholesterol plus esterified cholesterol). Column B was used as a pre-column which could be switched 'in' or 'out' in conjunction with column A for the estimation of TC or FC, respectively. A calibration between 1.0 and 8.0 mmol/l for FC and 0. 25 and 4.0 mmol/l for TC was obtained. For more than 2000 assays with the ET device a C.V. of less than 4% was obtained. The assay time was approximately 4 min per assay. The cholesterol estimations on the ET correlated well with similar estimations using a commercially available cholesterol diagnostic kit.

Biosensing Techniques↗
PubMed2005

Formaldehyde determination in seawater. Preliminary application to coastal samples at Terra Nova Bay (Antarctica).

A sensitive spectrofluorimetric-FIA (flow injection analysis) method for formaldehyde (HCHO) determination was improved with the aim of analysing seawater samples. The fluorescence emission versus HCHO concentration shows a linear pattern from sub microg L(-1) to about 1000 microg L(-1). The reproducibility at 15 ppb level is about 2%. Interferences from other aldehydes were checked; only glyoxal shows a significative interference, but only when its concentration is about 6000 times higher than that of formaldehyde. Superficial (microlayer, just sub-pack or sea-ice free sea surface) and deep (along the water column, sub-pack or in sea-ice free areas) seawater samples were collected near the coast at Terra Nova Bay (Ross Sea, Antarctica) during the 1998/1999 and 2001/2002 Italian Antarctic Expedition. We report here the preliminary results of the spectrofluorimetric-FIA determination of the HCHO content. The mean seawater superficial formaldehyde concentration was 15 microg L(-1); the concentration along the water column ranged between 4.5 to over 40 microg L(-1)(20 microg L(-1) mean concentration), usually with a maximum value for the 30 m depth, corresponding to a fluorescence maximum. The sampling was repeated 7 times in the austral summer in order to evaluate seasonal changes in the formaldehyde concentration/seawater depth profiles. The results show changes in the formaldehyde concentration at different depths.

Antarctic Regions↗
PubMed1998

An automatic determination of caffeine in soft drinks using flow injection system with amperometric detection.

An automatic procedure based on a flow injection analysis manifold has been developed for the determination of caffeine in soft drinks using an amperometric detection (+1.70 V vs AgCl/Ag). The sample and standards were injected without pre-treatment, with a sampling rate of 120 determinations per hour. The determination of caffeine in several soft drinks available in Portugal using the developed automatic system provided results with mean recovery values between 98% and 103% and a mean standard deviation between 2% and 5%. The results obtained were compared with those given by the reference method recommended by AOAC. Relative deviation was always less than 4%. Reproducibility of the method was assessed by the relative standard deviation (RSD%), values of which were less than 2%.

Beverages↗
PubMed2006

Change of the protein p53 electrochemical signal according to its structural form - quick and sensitive distinguishing of native, denatured, and aggregated form of the "guardian of the genome".

Presence of mutated and/or structurally modified (e.g., denatured, aggregated) protein p53 form is associated with several disorders such as Alzheimer's disease, Parkinson's disease, prion diseases, and many types of tumours. The aim of this work was to distinguish native, denatured and aggregated form of full-length p53 by flow injection analysis coupled with electrochemical detector (FIA-ED). Firstly FIA-ED method used for protein native form determination was optimized (detection limit 45.8 amol per 5 mul injection; 3 x S/N). In addition the technique was applied to identify p53 structural forms (denatured and aggregated). It was found out that denatured form provides about three times higher electrochemical response (protein structure unfolding, approach of more electroactive centers - aminoacid residues - towards electrode surface) in comparison with native form. On the other hand, aggregated form offers lower response (steric eclipse of electroactive protein parts) when compared with the signal of native form. The obtained data show that we are not only able to sensitively determine native, denatured, and aggregated structural forms of p53 protein but also to distinguish them.

Electrochemistry↗
PubMed2000

Development and optimisation of a flow injection assay for fluticasone propionate using an asymmetrical design and the variable-size simplex algorithm.

A flow injection analysis method is described to determine fluticasone propionate, based upon a novel adaptation of the reaction of o-phthalaldehyde with a thiol and a primary amine. The method, which allows both UV and fluorescence detection, has been optimised using experimental design. First a screening is executed to select the significant factors and in a second step these factors are optimised with the variable-size simplex algorithm. In the screening step, a two-level fractional factorial design is compared with an asymmetrical design containing the same number of experiments, but in which one factor is at three levels. It was found that in both designs the same significant variables are detected for the two-level factors, but that for the three-level factor the asymmetrical design confirms an expectation of having a (local) optimum in the examined domain, whilst from the two-level design this is not at all apparent. Complete optimisation was carried out for both UV and fluorescence detection. The two detection methods did not have the same significant variables. For the UV detection, the temperature and the pH adjustment on-line (concentration of sodium hydroxide and amount of boric acid) were the most critical parameters. For the fluorimetric detection the temperature and the fraction of methanol were critical. Moreover the conditions found to be optimal are different for both detection methods.

Algorithms↗
PubMed1994

Application of photochemical reaction in electrochemical detection of DNA intercalation.

A flow injection analysis (FIA) system for the detection of the compounds that intercalate within DNA is reported. A derivative of 9,10-anthraquinone has been used as the reference compound for photoelectrochemical detection. The sodium salts of 9,10-anthraquinone-2,6-disulfonic acid and 9,10-anthraquinone-2-sulfonic acid are photochemically activated and then reduced in the presence of an electron donor (glucose). The electrochemical signal is based on the measurement of the anodic current resulting from the oxidation of the reduced form of 9,10-anthraquinone. The reduced form of the 9,10-anthraquinone is oxidized through a mediated mechanism at the surface of a tetracyanoquinodimethane-(TCNQ)-modified graphite paste electrode covered by a Nucleopore membrane. TCNQ acts as an efficient mediator for the oxidation of reduced 9,10-anthraquinone. Cyclic voltammetry, photocyclic voltammetry, and the photoelectrochemical FIA response of 9,10-anthraquinone are reported. Experimental results show that these anthraquinones can be intercalated within the helix of double-stranded calf thymus DNA. The anthraquinone molecules that are intercalated within DNA cannot be oxidized due to their limited transport to the modified electrode surface. This results in a decrease in the anodic current at a constant concentration of anthraquinone after intercalation. There is a linear relation between the decrease in electrochemical response and the DNA concentration at a constant concentration of anthraquinone. The intercalated anthraquinone molecules can be completely replaced by another intercalating agent (i.e., ethidium bromide) that is more strongly intercalated within DNA, thereby regenerating the electrochemical response.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

[Determination of dopamine hydrochloride by a reverse flow injection chemiluminescence method].

A novel chemiluminescence system coupled with a reverse flow injection analysis for the determination of dopamine hydrochloride was presented. It is based on th e strong quench effect of dopamine hydrochloride on the chemiluminescence reaction between luminol and hexacyanoferrate(III) under alkaline condition. Various factors affecting the chemiluminescence intensity of the system were investigated. The possible mechanism of the proposed method was also studied. The decrease of chemiluminescence intensity was linear with the dopamine hydrochloride content in the range of 2.0 x 10(-9) -8.0 x 10(-7) g x mL(-1), the detection limit of the method was 1.14 x 10(-9) g x mL(-1), and the relative standard deviation was 0.99% (4.0 x 10(-7) g x mL(-1), n = 11). It was successfully used for the determination of the content of dopamine hydrochloride in dopamine hydrochloride injection.

Dopamine↗
PubMed2004

Fabrication of carbon microelectrodes with a micromolding technique and their use in microchip-based flow analyses.

In this paper, we report a new technique to pattern carbon microelectrodes for use in microfluidics. This technique, termed micromolding of carbon inks, uses poly(dimethylsiloxane)(PDMS) microchannels to define the size of the microelectrode. First, PDMS microchannels of the approximate dimensions desired for the microelectrode are made by soft lithography. The PDMS is then reversibly sealed to a substrate and the microchannels are filled with carbon ink. After a heating step the PDMS mold is removed, leaving a carbon microelectrode with a size slightly smaller than the original PDMS microchannel. The resulting microelectrode (27 microm wide and 6 microm in height) can be reversibly sealed to a PDMS-based flow channel. Fluorescence microscopy showed that no leakage occurred around the chip/electrode seal, even up to flow rates of 10 microL min(-1). The electrode was characterized by microchip-based flow injection analysis. Injections of catechol in Hank's Balanced Salt Solution (pH 7.4), showed a linear response from 2 mM to 10 microM (r(2)= 0.995), with a sensitivity of 56.5 pA microM(-1) and an estimated limit of detection of 2 microM (0.27 picomole, S/N=3). Reproducibility of the electrode response was shown by repeated injections (n= 10) of a 500 microM catechol solution, resulting in a RSD of 4.6%. Finally, selectivity was demonstrated by coating the microelectrode with Nafion, a perfluoronated cation exchange polymer. Dopamine exhibited a response at the modified microelectrode while ascorbic acid was rejected by the Nafion-coating. These electrodes provide inexpensive detectors for microfluidic applications while also being viable alternatives to use of other carbon microelectrode materials, such as carbon fibers. Furthermore, the manner in which the microelectrodes are produced will be of interest to researchers who do not have access to state of the art microfabrication facilities.

Carbon↗
PubMed1991

An FIA biosensor system for the determination of phosphate.

A flow injection analysis (FIA) biosensor system for the determination of phosphate was constructed using immobilized nucleoside phosphorylase and xanthine oxidase and an amperometric electrode (platinum vs silver/silver chloride, polarized at 0.7 V). When a phosphate-containing sample was injected into the detection cell, phosphate reacted with inosine in the carrier buffer to produce hypoxanthine and ribose-1-phosphate in the presence of nucleoside phosphorylase. Hypoxanthine was then oxidized by xanthine oxidase to uric acid and hydrogen peroxide, which were both detected by the amperometric electrode. The response of the FIA biosensor system was linear up to 100 microM phosphate, with a minimum detectable concentration of 1.25 microM phosphate. Each assay could be performed in 5-6 min and the system could be used for about 160 repeated analyses. This system was applicable for the determination of phosphate in various food products and plasma, and the results obtained agreed well with those of the enzymatic assay.

Biosensing Techniques↗
PubMed2007

Carbon film resistor electrode for amperometric determination of acetaminophen in pharmaceutical formulations.

Flow injection analysis (FIA) with amperometric detection was employed for acetaminophen quantification in pharmaceutical formulations using a carbon film resistor electrode. This sensor exhibited sharp and reproducible current peaks for acetaminophen without chemical modification of its surface. A wide linear working range (8.0x10(-7) to 5.0x10(-4) mol L(-1)) in phosphate buffer solution as well as high sensitivity (0.143 A mol(-1) L cm(-2)) and low submicromolar detection limit (1.36x10(-7) mol L(-1)) were achieved. The repeatability (R.S.D. for 10 successive injections of 5.0x10(-6) and 5.0x10(-5) mol L(-1) acetaminophen solutions) was 3.1 and 1.3%, respectively, without any memory effect between injections. The new procedure was applied to the analyses of commercial pharmaceutical products and the results were in good agreement with those obtained utilizing a spectrophotometric method. Consequently, this amperometric method has been shown to be very suitable for quality control analyses and other applications with similar requirements.

Acetaminophen↗
PubMed2004

Chemiluminescent immunosensor for CA19-9 based on antigen immobilization on a cross-linked chitosan membrane.

A novel chemiluminescent immunosensor for carbohydrate antigen 19-9 (CA19-9) based on the immobilization of CA19-9 on the cross-linked chitosan membrane was developed. The different membranes were characterized by atomic force microscopy (AFM) and infrared spectrum, respectively. Based on a noncompetitive immunoassay format, this proposed chemiluminescent immunosensor enabled a low-cost, flexible and rapid determination for CA19-9 in combination with flow injection analysis (FIA). After an off-line incubation of the analyte CA19-9 with horseradish peroxidase (HRP)-labeled anti-CA19-9, the mixture was injected into the immunosensor, which led to the trapping of free HRP-labeled anti-CA19-9 by the immobilized antigen in the immunosensor. The trapped HRP-labeled antibody was detected by chemiluminescence due to its catalytic activity following the reaction of luminol and H2O2. Under optimal conditions, the decreased chemiluminescent signal of the immunosensor was proportional to the CA19-9 concentration in the range of 2.0-25 U/ml with a detection limit of 1.0 U/ml. The immunosensor showed an acceptable accuracy and good reproducibility. The results of 20 human serum samples detected by this method were in acceptable agreement with those obtained by immunoradiometric assay. The proposed immunosensor provided a new promising tool for practical clinical detection of the serum CA19-9 level.

Antibodies↗
PubMed2004

Electro-oxidation and amperometric detection of chlorinated phenols at boron-doped diamond electrodes: a comparison of microcrystalline and nanocrystalline thin films.

We report on the electro-oxidation and amperometric detection of phenol and chlorinated phenols, the latter coupled with flow injection analysis (FIA) and high performance liquid chromatography (HPLC), using boron-doped microcrystalline and nanocrystalline diamond thin-film electrodes. The low background current, good response without extensive pretreatment, and low susceptibility to fouling are properties that make diamond an attractive new electrode for monitoring this class of pollutants. Cyclic voltammetric studies were performed to evaluate the redox response of phenol, 2-chlorophenol, 3-chlorophenol,4-chlorophenol, and pentachlorophenol (PCP) in phosphate buffer, pH 3.5, as a function of the potential scan rate and cycle number. The diamond electrode performance for the amperometric detection of these contaminants in FIA-EC and HPLC-EC was evaluated in terms of the linear dynamic range, limit of quantitation, sensitivity, response precision, and response stability. Both diamond types yielded low mass limits of quantitation of 100-1000 pg for all the phenolic compounds in FIA-EC, except PCP which was 3 ng, and 100-600 pg for all the compounds in HPLC-EC. In all cases, the S/N was 3 or greater. Both electrode types also exhibited good sensitivity, excellent response reproducibility (av 2.7% for FIA-EC and av 4.2% for HPLC-EC), and superb response stability for all the analytes. The electrodes could be used from days to weeks in the measurement with only a periodic soak in distilled 2-propanol required to maintain optimum performance. Both types of diamond outperformed glassy carbon, which exhibited short-lived responsiveness as a consequence of fouling by reaction products and potential-dependent changes in the electrode's physiochemical properties. The use of the HPLC-EC assay for the determination of 2-chlorophenol in a contaminated soil sample is also demonstrated.

Boron↗
PubMed2000

Flow injection monitoring and analysis of mixtures of hydrazine compounds using filter-supported bilayer lipid membranes with incorporated DNA.

This work describes a technique for the rapid and sensitive electrochemical flow injection monitoring and analysis of mixtures of hydrazine compounds using stabilized systems of filter-supported bilayer lipid membranes (BLMs) composed of egg phosphatidylcholine (egg PC) with incorporated DNA. Injections of hydrazines were made into flowing streams of a carrier electrolyte solution, and a transient current signal with a duration of seconds reproducibly appeared in less than one min after exposure of the DNA-modified lipid membranes to the hydrazines. The magnitude of this signal was linearly related to the concentration of hydrazines, which could be determined at sub-micromolar levels. Repetitive cycles of injection of hydrazines have shown no signal degradation during each cycle (30 sequential injections). The time of appearance of the transient response was different for each hydrazine and increased in the order of hydrazine, methylhydrazine or dimethylhydrazine, and phenylhydrazine. The difference in time of response has allowed selective detection and analysis of these hydrazines in mixtures.

DNA↗
PubMedDate not supplied

Flow-injection chemiluminescence determination of catecholamines based on their enhancing effects on the luminol-potassium periodate system.

A rapid and sensitive chemiluminescence (CL) method using flow injection analysis is described for the determination of four catecholamines, dopamine, adrenaline, isoprenaline and noradrenaline, based on their greatly enhancing effects on the CL reaction of luminol-potassium periodate in basic solutions. The optimized chemical conditions for the chemiluminescence reaction were 1.0 x 10(-4) mol/L luminol and 1.0 x 10(-5) mol/L potassium periodate in 0.2 mol/L sodium hydroxide (NaOH). Under the optimized conditions, the calibration graphs relating the CL signal intensity (peak height) to the concentration of the analytes were curvilinear and they were suitable for determining dopamine, adrenaline, isoprenaline, and noradrenaline in the range 0.1-10 ng/mL, 0.1-100 ng/mL, 1-100 ng/mL and 5-50 ng/mL, respectively, with the relative standard deviations of 0.8-1.7%. The detection limits of the method are 0.02 ng/mL for dopamine, 0.01 ng/mL for adrenaline, 0.1 ng/mL for isoprenaline and 2.0 ng/mL for noradrenaline. The sampling frequency was calculated to be about 60/h. The selectivity of the method was good, because a series of common ions or excipients, such as K(+), Ba(2+), CO(3)(2-), NO(3)(-), SO(4)(2-), PO(4)(3-), sodium citrate, sodium bisulphite, oxidate dopamine, starch, lactose, carbamide and gelatin, could not produce interference when their concentrations were 1000-fold than those of dopamine. The present method was successfully applied to the determination of the four catecholamines in pharmaceutical injections.

Catecholamines↗
PubMed2003

Amperometric and spectrophotometric determination of carbaryl in natural waters and commercial formulations.

The work presented describes the development and evaluation of two flow-injection analysis (FIA) systems for the automated determination of carbaryl in spiked natural waters and commercial formulations. Samples are injected directly into the system where they are subjected to alkaline hydrolysis thus forming 1-naphthol. This product is readily oxidised at a glassy carbon electrode. The electrochemical behaviour of 1-naphthol allows the development of an FIA system with an amperometric detector in which 1-naphthol determination, and thus measurement of carbaryl concentration, can be performed. Linear response over the range 1.0 x 10(-7) to 1.0 x 10(-5) mol L(-1), with a sampling rate of 80 samples h(-1), was recorded. The detection limit was 1.0 x 10(-8) mol L(-1). Another FIA manifold was constructed but this used a colorimetric detector. The methodology was based on the coupling of 1-naphthol with phenylhydrazine hydrochloride to produce a red complex which has maximum absorbance at 495 nm. The response was linear from 1.0 x 10(-5) to 1.5 x 10(-3) mol L(-1) with a detection limit of 1.0 x 10(-6) mol L(-1). Sample-throughput was about 60 samples h(-1). Validation of the results provided by the two FIA methodologies was performed by comparing them with results from a standard HPLC-UV technique. The relative deviation was <5%. Recovery trials were also carried out and the values obtained ranged from 97.0 to 102.0% for both methods. The repeatability ( RSD, %) of 12 consecutive injections of one sample was 0.8% and 1.6% for the amperometric and colorimetric systems, respectively.

Carbaryl↗