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PubMed1995

Electrochemical dehydrogenase-based homogeneous assays in whole blood.

An electrochemical method has been developed for determining NADH in whole blood for dehydrogenase-based assays by flow-injection analysis. NADH generated by dehydrogenase is oxidized by an electron-transfer coupling reagent, 2,6-dichloroindophenol (DCIP). The reduced form of DCIP (DCIPH2) is measured amperometrically by flow-injection analysis. Endogenous interferents were inhibited by p-hydroxymercuribenzoate. Electrode fouling by proteins was not observed under assay conditions. The Emit theophylline enzyme immunoassay and the hexokinase glucose assay were used as models. For the glucose assay, the intraassay CVs were 15% at 0.31 g/L and 3.5% at 1.82 g/L. Recoveries of glucose from whole blood (compared with that for aqueous standards) were 109%, 97.9%, and 101% at 0.050, 2.00, and 5.00 g/L glucose, respectively, and 104%, 101%, and 102% for theophylline at concentrations of 5.0 (low), 16.4 (medium), and 30.2 (high) mg/L, respectively, with corresponding precisions of 12%, 9.5%, and 8.8%. Both assays correlated well with results by reference methods. These studies demonstrate that this method can measure NADH in whole blood without prior separation and that it is potentially applicable to other dehydrogenase-based assays in whole blood.

2,6-Dichloroindophenol↗
PubMed2002

Electrochemical analysis of acetaminophen using a boron-doped diamond thin film electrode applied to flow injection system.

The electrochemistry of acetaminophen in phosphate buffer solution (pH 8) was studied at a boron-doped diamond (BDD) thin film electrode using cyclic voltammetry, hydrodynamic voltammetry, and flow injection with amperometric detection. Cyclic voltammetry was used to study the reaction as a function of concentration of analyte. Comparison experiments were performed using a polished glassy carbon (GC) electrode. Acetaminophen undergoes quasi-reversible reaction at both of these two electrodes. The BDD and GC electrodes provided well-resolved cyclic voltammograms but the voltammetric signal-to-background ratios obtained from the diamond electrode were higher than those obtained from the GC electrode. The diamond electrode provided a linear dynamic range from 0.1 to 8 mM and a detection of 10 microM (S/B approximately 3) for voltammetric measurement. The flow injection analysis results at the diamond electrode indicated a linear dynamic range from 0.5 to 50 microM and a detection limit of 10 nM (S/N approximately 4). Acetaminophen in syrup samples has also been investigated. The results obtained in the recovery study (24.68+/-0.26 mg/ml) were comparable to those labeled (24 mg/ml).

Acetaminophen↗
PubMed2006

Cost-effective flow cell for the determination of malachite green and leucomalachite green at a boron-doped diamond thin-film electrode.

An electrooxidation and a cost-effective flow-based analysis of malachite green (MG) and leucomalachite green (LMG) were investigated at a boron-doped diamond thin-film (BDD) electrode. Cyclic voltammetry as a function of the pH of the supporting electrolyte solution was studied. Comparison experiments were performed with a glassy carbon electrode. A well-defined cyclic voltammogram, providing the highest peak current, was obtained when using phosphate buffer at pH 2. The potential sweep-rate dependence of MG and LMG oxidation (peak currents for 1 mM MG and LMG linearly proportional to v 1/2, within the range of 0.01 to 0.3 V/s) indicates that the oxidation current is a diffusion-controlled process on the BDD surface. In addition, hydrodynamic voltammetry and amperometric detection using the BDD electrode combined with a flow injection analysis system was also studied. A homemade flow cell was used, and the results were compared with a commercial flow cell. A detection potential of 0.85 V was selected when using a commercial flow cell, at which MG and LMG exhibited the highest signal-to-background ratios. For the homemade flow cell, a detection potential of 1.1 V was chosen because MG and LMG exhibited a steady response. The flow analysis results showed linear concentration ranges of 1-100 microM and 4-80 microM for MG and LMG, respectively. The detection limit for both compounds was 50 nM.

Aniline Compounds↗
PubMed2003

Real time kinetic analysis of the interaction between immunoglobulin G and histidine using quartz crystal microbalance biosensor in solution.

Quartz crystal microbalance (QCM) biosensor integrated in a flow injection analysis (FIA) system was used for the investigation of the specific interaction between immunoglobin G (IgG) and histidine. The histidine was immobilized on the gold electrodes of the piezoelectric crystal using appropriate procedures based on self-assembling of the dithiothreitol (DTT). The specific interaction of the immobilized ligand with IgG in solution was followed as a change in the resonant frequency of the modified crystal and studied in real time without any additional labels. With the mass sensitive biosensor system, the differences in affinity of three different species of IgG: human IgG, goat IgG and mouse IgG were easily distinguished and their respective kinetic rate constants (kass and kdiss) and equilibrium association constants (KA) were determined from the curves of frequency versus time. For the interactions, KA were 2.92 x 10(4), 3.23 x 10(4) and 4.08 x 10(4) M(-1) for human IgG, goat IgG and mouse IgG, respectively.

Adsorption↗
PubMed2003

Mobile phase compensation to improve NMR spectral properties during solvent gradients.

A solvent compensation method based on flow injection analysis is used to obtain high quality nuclear magnetic resonance (NMR) spectra during solvent gradients. Using a binary solvent system containing D2O and CD3OD, NMR line broadening and chemical shift changes are observed with a 10% methanol per min solvent composition gradient. However, by creating a second equal but reverse gradient and combining the two solvent gradients before the NMR detector, the composition of solvent reaching the NMR flow cell is kept constant. We demonstrate a system using flow injection analysis of combining solvent gradients and show constant NMR spectral performance as a function of time as the combined flow has a constant solvent composition irrespective of the initial solvent gradient. Using this approach, methods can be developed to measure high quality NMR spectra during on-flow gradient LC-NMR experiments. The ultimate ability of this approach depends on the ability to compensate for the disturbance of the solvent gradient and reverse gradient by a pair of LC columns (the analytical and reverse gradient columns).

Chromatography, High Pressure Liquid↗
PubMed1996

On-line competitive immunoassay for insulin based on capillary electrophoresis with laser-induced fluorescence detection.

An on-line competitive immunoassay for insulin has been developed and applied to monitoring insulin concentration in a flowing stream. In the assay, solutions of fluorescein-labeled insulin (FITC-insulin), monoclonal anti-insulin, and sample containing insulin are pumped into a cross where they begin to mix. The mixture flows through a fused silica reactor capillary to a flow-gated interface. During transfer to the interface, insulin and FITC-insulin compete to form a complex with the antibody. At the interface, a plug of the mixture is injected into a separation capillary, where the bound and free FITC-insulin are separated and detected by capillary electrophoresis with laser-induced fluorescence detection. The amount of bound FITC-insulin, amount of free FITC-insulin, or bound/free ratio can be used to quantify insulin concentration. Typical relative standard deviations of bound over free ratio are 5%. The detection limit of the immunoassay in the on-line mode is < 0.3 nM. Each separation requires as little as 3 s, and over 1600 consecutive assays can be acquired with no need to rinse the separation capillary. Thus, the system can be used to monitor insulin in a flowing stream for flow injection analysis or for sensor-like monitoring. Dilution and zone broadening during transfer of sample to the interface limit the response time of the on-line system to about 25 s. As a demonstration of the on-line immunoassay, the insulin content of single islets of Langerhans was determined by flow injection analysis.

Electrophoresis, Capillary↗
PubMed1996

Lactate solid-state biosensor with multilayer of electrodeposited polymers for flow-injection clinical analysis.

In the lactate biosensor, electrodeposited poly(o-phenylenediamine) serves as a convenient matrix for the immobilization of lactate oxidase, but does not provide sufficient discrimination from several interfering species present in physiological fluids. Their effect, however, can be eliminated by additional modification of the working Pt electrode with a bilayer of electrodeposited polypyrrole/polyphenol. Despite continued decrease in biosensor sensitivity, the newly developed three-layer solid-state biosensor was successfully applied in flow-injection determination of lactate in both undiluted and diluted human blood serum samples over a 10 day period. For the lactate concentration range 0.2-5.0 mM in several series of measurements the correlation coefficient values for comparison with photometric determination using a DuPont dimension clinical analyzer were between 0.96 and 0.99. The reproducibility measured for 1:10 diluted serum was 0.6%. The detection limit was estimated as 2 microM.

Acetaminophen↗
PubMed2006

A near real-time system for continuously monitoring airborne subtilisin-type enzymes in the industrial atmosphere.

We describe the development and validation of a portable system comprising an air sampler coupled to an automated flow injection analysis device. The system is able to monitor airborne concentrations of subtilisin-type enzymes in the workplace atmosphere on a continuous basis. Sampling is in two stages: using a sampling head that is designed to mimic human respiration at approx. 1 m s(-1) at a sampling rate of 600 l min(-1). In the second stage, the captured particles are deposited by impaction from the air stream onto the inner surface of a cyclone that is continuously washed with a jet of buffer solution. Deposited particles are then washed into a reservoir from which samples are taken every 5-6 min and injected automatically into a continuous flow injection analysis system. Proteolytic enzyme in the sample passes through a bioreactor maintained at about 40 degrees C. This contains a cellulose solid phase matrix on which is covalently immobilised Texas Red-labelled gelatin as substrate. The passing enzyme partially digests the substrate releasing fluorophore that is detected down stream in a flow cell coupled to a fluorimeter. The system is calibrated using enzyme standards and the intensity of the resulting peaks from the ex-air samples is converted to airborne concentrations using a mathematical model programmed into a PC. The system has a limit of detection of 4.8 ng m(-3) and a dynamic range of 5-60 ng m(-3). The within assay precision (RSD) is 6.3-9.6% over this range. The within batch precision is 20.3% at 20 ng m(-3) and the corresponding between batch value is 19.5%. The system has been run for periods up to 8 h in the laboratory and for up to 4 h at a factory site and the values obtained compared with time-averaged values obtained from a conventional Galley sampler and in-house analysis when reasonable agreement of the results was observed. The stability of the system over 21 days of continuous use with standards injected periodically was studied. Linearity was observed for all the standard plots throughout. At the end of 21 days, after a total exposure equivalent to 2395 ng ml(-1) of Savinase, the signal due to the 5.0 ng ml(-1) standard was still easily detectable.

Air Pollutants, Occupational↗
PubMed2000

[Development of trace metal ion analysis].

Analyses of trace biologically essential or toxic ionic compounds found in the environment are very important. However, the lack of sensitivity and interference caused by coexisting components are often serious problems. To determine trace levels of metal ions without the above problems, new preconcentration and analytical methods have been developed. Firstly, three methods for the selective preconcentration of metal ions are shown below: 1) 3-Chloropyridazine-6-carbohydrazide was immobilized on glass beads supports to be used as a column packing material. Multi-metal ions were concentrated on the column and eluted selectively with several buffers and hydrochloric acid. The eluate was analyzed off-line by flame atomized-atomic absorption spectrometry (AAS). This method was able to determine sub-ppb levels of cupper- and cadmium-ions in environmental samples. 2) Salicylideneamino-2-thiophenol was immobilized on the supports. Aluminum ion was concentrated selectively on the column and eluted with nitric acid. The eluate was analyzed off-line by flameless-AAS or on-line by flow injection analysis using pyrocatechol violet for a post-column colorimetric reagent. These methods were able to determine ppb-ppt levels of aluminium in environmental samples and were suitable for its state-analysis. 3) Bathocuproinesulfonic acid was immobilized on the supports. Copper ion was concentrated selectively on the column and eluted with nitric acid. The eluate was analyzed on-line by flow injection analysis using bathocuproinesulfonic acid. This method was able to determine sub-ppb levels of copper in environmental samples. On the other hand, to analyze simultaneously trace metal ions and anions, capillary electrophoresis was performed using ethylenediaminetetraacetic acid as an electrolyte component. Simultaneous determination of several ions in mineral waters was achieved by the system.

Chelating Agents↗
PubMed2006

Consequences of vapor enhancement on selenium speciation analysis by HPLC/ICPMS.

Recent work has shown the presence of volatile selenium metabolites in human urine and suggested that these compounds could compromise quantitative selenium analyses by ICPMS. We show that with a commonly used sample introduction system (pneumatic nebulizer and spray chamber), two volatile selenium species recently identified in urine, namely, dimethyl selenide and dimethyl diselenide, gave greatly increased ICPMS responses (up to 58-fold) relative to selenite, an effect related to their volatilization in the spray chamber resulting in enhanced transport to the plasma. The quantitative consequences of this effect were demonstrated by measurement of total selenium and selenium species in certified reference material, NIES CRM 18 human urine. Direct flow injection analysis of the urine gave a total selenium concentration more than 2-fold higher than the certified value. These data suggested that NIES CRM 18 may contain part of its selenium as volatile species, and subsequent reversed-phase HPLC/ICPMS showed the presence of dimethyl selenide in addition to selenosugars and trimethylselenonium ion. Although the practice of quantifying unidentified chromatographic peaks against those of known compounds is common in speciation analysis, this approach when applied to NIES CRM 18 gave a value for the sum of selenium species which was twice the certified total selenium concentration. This work shows that the presence of volatile selenium species in urine precludes the use of flow injection analysis for total selenium measurements and imposes severe restrictions on the quantification of urinary selenium metabolites. In addition, it raises broader issues of the validity of the "dilute and shoot" approach to the determination of metals in clinical analysis of biological fluids.

Chromatography, High Pressure Liquid↗
PubMed2002

Development and testing of a detection method for liquid chromatography based on aerosol charging.

Aerosol-based detection methods for HPLC in which HPLC effluent is converted to an aerosol and detected optically have been employed in the past. This paper describes a new aerosol-based detection method for HPLC, which we name aerosol charge detection. This detection method also involves generation of an aerosol but with aerosol detection by charging aerosol particles and measuring the current from the charged particle flux. A commercial electrical aerosol size analyzer was used for the aerosol detection. The constructed detector was tested using flow injection analysis with water as the mobile phase, and the signal response was found to be linear for sodium sulfate over the concentration ranges of 0.2-100 microg mL(-1) using one of the nebulizers. Minimum mass and concentration detection limits using the more efficient nebulizer were estimated to be 0.2 ng and 10 ng mL(-1), respectively. Behavior for most of the other compounds tested was similar with some differences in sensitivity. Testing the detector using reversed phase HPLC for glucose gave a range of linear response and detection limits that were similar to the flow injection analysis studies. Under most HPLC conditions, the noise will primarily be a function of solvent impurities; however, the electrical aerosol size analyzer allows the removal of small charged particles to improve the signal-to-noise ratio.

Journal Article↗
PubMed2006

Spectrophotometric determination of fluoxetine by batch and flow injection methods.

A rapid, simple, and accurate spectrophotometric method is presented for the determination of fluoxetine by batch and flow injection analysis methods. The method is based on fluoxetine competitive complexation reaction with phenolphthalein-beta-cyclodextrin (PHP-beta-CD) inclusion complex. The increase in the absorbance of the solution at 554 nm by the addition of fluoxetine was measured. The formation constant for fluoxetin-beta-CD was calculated by non-linear least squares fitting. Fluoxetine can be determined in the range 7.0 x 10(-6)-2.4 x 10(-4) mol l(-1) and 5.0 x 10(-5)-1.0 x 10(-2) mol l(-1) by batch and flow methods, respectively. The limit of detection and limit of quantification were respectively 4.13 x 10(-6) mol l(-1) and 1.38 x 10(-5) mol l(-1) for batch and 2.46 x 10(-5) mol l(-1) and 8.22 x 10(-5) mol l(-1) for flow method. The sampling rate in flow injection analysis method was 80+/-5 samples h(-1). The method was applied to the determination of fluoxetine in pharmaceutical formulations and after addition to human urine samples.

Antidepressive Agents↗
PubMed1998

A theoretical equation describing the time evolution of the concentration of a selected range of substrate molecular weights in depolymerization processes mediated by single-attack mechanism endo-enzymes.

Monitoring the time evolution of the concentration of a selected range of molecular weights of substrate, referred to as "detectable" substrate, has been used to determine endo-enzymic activities in polysaccharide depolymerizing processes. In the methodologies based on the use of dye-labeled substrates, the "detectable" substrate extends from a given molecular weight threshold downward. On the contrary, in the fluorescent probe-flow injection analysis methodology, initially developed to determine (1 --> 3)-(1 --> 4)-beta-D-glucanase activities, the "detectable" substrate extends from a given molecular weight threshold upward. Assuming that the time evolution of the molecular weight distribution of the substrate follows the most probable distribution (the enzymic attack is random and its mechanism is single attack), a theoretical equation describing the time evolution of the concentration of "detectable" substrate (from a given molecular weight threshold upward or downward) has been deduced. This equation, Wd = Wo. (1 + alphat). e-alphat, where Wd is the concentration of "detectable" substrate, Wo is the initial concentration of the substrate, t is the depolymerization time, and alpha is a parameter correlated through a hyperbola with the initial concentrations of enzyme and substrate and the Michaelis-Menten constant, Km, has been tested against different (1 --> 3)-(1 --> 4)-beta-D-glucan/(1 --> 3)-(1 --> 4)-beta-D-glucanase systems using the fluorescent probe-flow injection analysis methodology and Calcofluor as the fluorescent probe. The most important predictions of the theoretical equation, which allow accurate determination of both endo-enzymic activities and kinetic constants, have been experimentally confirmed.

Benzenesulfonates↗
PubMed1994

Flow injection determination of glutamate in human serum and rat brain samples with immobilized glutamate oxidase and glutamate dehydrogenase reactors.

Two methods are proposed for the determination of regional concentrations of glutamate in the rat brain as well as in human serum. Glutamate oxidase was immobilized on non-porous glass beads and glutamate dehydrogenase was immobilized on glass derivatives. These supports were employed for the construction of Single Bead String Reactors and Packed Bed Reactors, respectively, which in turn were linked to Flow Injection Analysis systems with either photometric or fluorometric detection. Analytical working curves are linear in the range 1-200 mumol/l for packed bed reactors and 10-500 mmol/l for single bead string reactors. The samples were pretreated depending on their origin and the applied measuring system. Optimal dilution factors were established for the two techniques. Optimal dilution ratios were established and the influence of several added substances was investigated. Recovery and method comparison studies including high performance liquid chromatography verified the accuracy of the proposed methods. Results from within-day and between-day measurements gave relative standard deviations of 4.7 and 5.9% for serum samples and 2.5 and 4.0% for brain samples, respectively.

Amino Acid Oxidoreductases↗
PubMed2004

Determination of SCH 211803 by nanoelectrospray infusion mass spectrometry: evaluation of matrix effect and comparison with liquid chromatography-tandem mass spectrometry.

A high throughput assay for SCH 211803, an M2 muscarinic receptor antagonist in human plasma using nanoelectrospray infusion tandem mass spectrometry is described. Sample processing consisted of protein precipitation followed by solid phase extraction using octadecasilyl resin-filled pipette tips on a liquid handling robotic system. The sample extracts were infused directly to the mass spectrometer using a nanoelectrospray interface in a silicon chip format. SCH 211803 was quantified in plasma over the concentration range of 1-1000 ng/mL. In comparison with a liquid chromatography-tandem mass spectrometry assay, the nanoelectrospray method has comparable accuracy, precision and limit of quantitation, with a nine-fold improvement in sample throughput. Using the nanoelectrospray assay, ion suppression was evaluated and found to be 15%. This represented a four-fold reduction in matrix suppression when compared to a conventional electrospray source operating in the flow injection analysis mode at a flow rate common for LC-MS/MS analysis.

Animals↗
PubMed1998

Cefuroxime selective electrodes for batch and FIA determinations in pharmaceutical preparations.

Different cefuroxime selective electrodes, without internal reference solution and comprising PVC membranes, were constructed and evaluated. Membranes were prepared with cefuroxime tetraoctylammonium (A) or cefuroxime bis(triphenylphosphoranylidene)ammonium (B) as ion-exchanger, 2-nitrophenyl octyl ether (X) or bis(2-ethylhexyl)sebacate (Y) as plasticizing mediator solvent and 4-tert-otcylphenol (TOP) as additive. From the comparative evaluation of the described electrodes, membranes comprising 2-nitrophenyl octyl ether, cefuroxime tetraoctylammonium and 4-tert-otcylphenol presented better working characteristics. For these electrodes (type XA-TOP), with a lifetime > 5 months, a lower limit of linear range of 2.8 x 10(-4) M, a practical detection limit of 1.3 x 10(-4) M, a reproducibility of approximately +/-0.6 mV day(-1) and a slope of -50.4 mV decade(-1), under H3PO4/NaH2PO4 solutions (pH 3.5; I =0.1 M), were found. The presence of the additive on the membranes was of crucial importance for the electrodes good characteristics. Interference from sulphate, chloride, nitrate, iodide, cefaclor, cefadroxil, cefazolin and cephradine, on the electrodes behaviour was evaluated. Only a slight interference from nitrate and iodide was recorded, being type XA-TOP electrodes the most selective units. Electrodes with a tubular configuration prepared with type XA-TOP membranes, aiming flow injection analysis, were also constructed. When these tubular potentiometric detectors were evaluated in a double-channel flow injection manifold, with 3.5 pH and 0.1 M ionic strength conditions, significantly better working characteristics than those of the corresponding conventional electrodes, namely higher slopes (-54.6 mV decade(-1)) and better reproducibilities (+/-0.2 mV day(-1)), were found. Both conventional and tubular type XA-TOP electrodes were used for injections analyses by batch and FIA, respectively, presenting low consumption of samples and reagents. Relative error deviations to the reference procedures <3.0% were found.

Cefuroxime↗
PubMed2002

Validation of the Willems badge diffusive sampler for nitrogen dioxide determinations in occupational environments.

The Willems badge, a diffusive sampler for nitrogen dioxide, has previously been validated for ambient air measurements. This paper describes the laboratory and field validation of the Willems badge for personal sampling under working environment conditions. The mean sampling rate in the laboratory tests was 46 ml min(-1), with an RSD of 12%. No statistically significant effects on sampling rate of the sampling time, concentration of NO2 or relative humidity were found. A slightly decreased sampling rate was observed at low wind velocity. This was also confirmed during static sampling, which makes the sampler less appropriate for static sampling indoors. No back diffusion was observed. Storage of the samplers for two weeks before or after exposure did not affect the sampling rate. Our analysis is based on a modified colorimetric method, performed by FIA (flow injection analysis). This technique was compared to ion chromatography analysis. The use of ion chromatography lowered the detection limit from 11 to 2 microg m(-3) for an 8 h sample, and furthermore enabled the detection of other anions. In conclusion, the diffusive sampler was found to perform well for personal measurements in industrial environments.

Air Pollutants↗
PubMed2000

Simultaneous monitoring of glucose and lactate by an interference and cross-talk free dual electrode amperometric biosensor based on electropolymerized thin films.

An interference and cross-talk free dual electrode amperometric biosensor integrated with a microdialysis sampling system is described, for simultaneous monitoring of glucose and lactate by flow injection analysis. The biosensor is based on a conventional thin layer flow-through cell equipped with a Pt dual electrode (parallel configuration). Each Pt disk was modified by a composite bilayer consisting of an electrosynthesised overoxidized polypyrrole (PPYox) anti-interference membrane covered by an enzyme entrapping gel, obtained by glutaraldehyde co-crosslinking of glucose oxidase or lactate oxidase with bovine serum albumin. The advantages of covalent immobilization techniques were coupled with the excellent interference-rejection capabilities of PPYox. Ascorbate, cysteine, urate and paracetamol produced lactate or glucose bias in the low micromolar range; their responses were, however, completely suppressed when the sample was injected through the microdialysis unit. Under these operational conditions the flow injection responses for glucose and lactate were linear up to 100 and 20 mM with typical sensitivities of 9.9 (+/- 0.1) and 7.2 (+/- 0.1) nA/mM. respectively. The shelf-lifetime of the biosensor was at least 2 months. The potential of the described biosensor was demonstrated by the simultaneous determination of lactate and glucose in untreated tomato juice samples; results were in good agreement with those of a reference method.

Animals↗