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PubMed2000

Determination of cadmium by flow injection-chemical vapor generation-atomic absorption spectrometry.

A method was developed for the generation of a "cold vapor" of cadmium by means of flow injection-chemical vapor generation from aqueous samples, the determination being conducted with an atomic absorption spectrometer (Pyrex glass T-cell). Several gas-liquid separator designs, atomizer designs, and the effect of several reagents previously reported as sensitivity enhancers (including cobalt, nickel, thiourea and didodecyl-dimethylammonium bromide) were investigated. The limit of detection, calculated as the concentration giving a signal equal to three times the standard deviation of the blank, was 16 ng L(-1), and the relative standard deviation was 1.4% for a concentration of 2 microg L(-1) and 3.8% for 0.1 microg L(-1). The addition of nickel and thiourea to the samples provided improved tolerance to the interference of coexisting ions. Two NIST certified reference materials, Montana Soil and Apple Leaves (respectively containing 41.7+/-0.25 mg kg(-1) Cd and 0.013+/-0.002 mg kg(-1) Cd) were accurately analyzed. The interference of lead was overcome by coprecipitation with barium sulfate, and the experimental values obtained were 41+/-1 mg kg(-1) Cd and 0.013+/-0.002 mg kg(-1) Cd, respectively.

Cadmium↗
PubMed2001

Flow-injection spectrophotometric multidetermination of metallic ions with a single reagent exploiting multicommutation and multidetection.

A flow system designed by computer-controlled discrete commutation devices is proposed for the multidetermination of metallic ions with a single chromogenic reagent. Intermittent addition of masking agents and changes of the reaction pH were exploited to implement selective determination of four species. Multidetection with an optical-fiber CCD-array spectrophotometer enabled simultaneous measurements at different wavelengths for multidetermination. The proposed system was applied to the determination of iron, copper, nickel and zinc in alloys and pharmaceutical preparations, yielding results in agreement with those obtained by flame atomic absorption spectrophotometry at the 95% confidence level. The sampling rate was estimated to be 80 determinations per hour. Coefficients of variation lower than 2% (n = 20) were achieved for all species.

Alloys↗
PubMed2001

Mercury speciation by HPLC--cold-vapour radiofrequency glow-discharge optical-emission spectrometry with on-line microwave oxidation.

Hollow-cathode (HC) radiofrequency glow-discharge (rf-GD) optical-emission spectrometry (OES) has been used as detector for the determination of inorganic mercury by cold-vapour (CV) generation in a flow-injection (FI) system. Both NaBH4 and SnCl2 were evaluated as reducing reagents for production of mercury CV. The conditions governing the discharge (pressure, He flow rate, and delivered power) and Hg CV generation (NaBH4 or SnCl2 concentration and reagent flow rate) were optimized using both reducing agents. The analytical performance characteristics of FI-CV-rf-GD-OES for mercury detection were evaluated at the 253.6 nm emission mercury line. Detection limits (DL) of 0.2 ng mL(-1) using SnCl2 and 1.8 ng mL(-1) using NaBH4 were obtained (100 microliter sample injections were used). When the optimized experimental conditions using SnCl2 had been determined, the analytical potential of this CV-rf-GD-OES method was investigated as on-line detector for high-performance liquid chromatographic (HPLC) speciation of mercury (Hg(II) and methylmercury). The HPLC-CV-rf-GD-OES detection limits for 100 microliter sample injections were found to be 1.2 and 1.8 ng mL(-1) (as mercury) of inorganic mercury and methylmercury, respectively. The reproducibility observed was below +/- 8% for both species. Finally, the HPLC-CV-rf-GD-OES system developed was successfully applied to the determination of methylmercury (speciation) in two certified reference materials, Dorm-2 and Dolt-2.

Borohydrides↗
PubMed2004

Anion interactions with Na,K-ATPase: simultaneous binding of nitrate and eosin.

Nucleotide binding affinity to Na,K-ATPase is reduced by a number of anions such as nitrate and perchlorate in comparison with affinity in the presence of chloride (all with sodium as the cation). The reduction correlates with the position of these anions in the Hofmeister series. Transient kinetic experiments using the fluorescent dye eosin-which binds to the nucleotide site of the Na,K-ATPase-show that simultaneous anion binding, exemplified with nitrate, and eosin binding is possible. The effect of nitrate on eosin binding is reflected in a decreased binding-rate constant and an increased dissociation rate constant, leading to a decreased equilibrium binding constant for eosin. Since eosin binding is analogous with nucleotide binding to Na,K-ATPase, the results suggest the simultaneous presence of nucleotide and anion binding sites.

Adenosine Diphosphate↗
PubMed2006

The study of neural network-based controller for controlling dissolved oxygen concentration in a sequencing batch reactor.

The design and development of the neural network (NN)-based controller performance for the activated sludge process in sequencing batch reactor (SBR) is presented in this paper. Here we give a comparative study of various neural network (NN)-based controllers such as the direct inverse control, internal model control (IMC) and hybrid NN control strategies to maintain the dissolved oxygen (DO) level of an activated sludge system by manipulating the air flow rate. The NN inverse model-based controller with the model-based scheme represents the controller, which relies solely upon the simple NN inverse model. In the IMC, both the forward and inverse models are used directly as elements within the feedback loop. The hybrid NN control consists of a basic NN controller in parallel with a proportional integral (PI) controller. Various simulation tests involving multiple set-point changes, disturbances rejection and noise effects were performed to review the performances of these various controllers. From the results it can be seen that hybrid controller gives the best results in tracking set-point changes under disturbances and noise effects.

Algorithms↗
PubMed2005

Segmenting fluid effect on PCR reactions in microfluidic platforms.

This paper evaluates the compatibility of segmenting fluids for two phase flow applications in biomedical microdevices. The evaluated fluids are chosen due to the variations in fluid properties and cost, while also reflecting their use in the recent literature. These segmenting fluids are examined to determine their compatibility with the Polymerase Chain Reaction (PCR), through controlled experiments. The results are the first to provide a quantitative measure of segmenting fluid compatibility with PCR.

Chemical Fractionation↗
PubMed1993

Enzyme reactor for urinary acylcarnitines assay by reversed-phase high-performance liquid chromatography.

An immobilized enzyme reactor, made up acylcarnitine hydrolase, carnitine dehydrogenase and diaphorase in sequence, was developed for the sensitive and selective determination of urinary free and individual acylcarnitines by a reversed-phase high-performance liquid chromatography. A 100-microliter urine sample was directly injected onto the TSKgel ODS 80Ts column and eluted by a step-gradient procedure. The eluent was mixed with the substrate solution of beta-NAD+ (1.0 mmol/l), resazurin (25 mumol/l) and Tris acetate (0.2 mol/l, pH 9.0). The mixture was passed through the immobilized enzyme reactor at 40 degrees C. Acylcarnitines were hydrolyzed and the converted to rezorufin which was measured by monitoring the fluorescence intensity at lambda EX = 560 nm and lambda EM = 580 nm. Free, acetyl-, glutaryl-, propionyl-, butyryl-, isobutyryl-, valeryl- and isovalerylcarnitine were determined within 55 min with detection limits (< 1 mumol/l) and within-run and day-to-day imprecision (C.V. < 6%). Free, acetyl- and isobutyrylcarnitine were found in normal urine. On the other hand, propionylcarnitine was detected in the urine of children with propionic aciduria and methylmalonic aciduria and multiple acylcarnitines were found in the urine of children with glutaric aciduria (type II).

Acetylcarnitine↗
PubMed1992

Process monitoring by flow-injection immunoassay. Evaluation of a sequential competitive binding assay.

A new variation on the theme of flow-injection binding assays is presented, namely the sequential competitive binding assay, in which the sample containing the native antigen is first introduced into the flow system followed by a pulse of labelled antigen. The flow-injection binding assay was used in monitoring the effluent from column chromatographic separations of proteins. By applying a computer-based evaluation system, concentrations are automatically read and compensation is made for denaturation in the affinity sorbent.

Binding, Competitive↗
PubMed1994

Cyanide dissociation from the hemoglobin of Parascaris equorum.

The reduction of cyanomethemoglobin by dithionite leads to the appearance of an intermediate, the complex of cyanide with ferrous hemoglobin, whose dissociation is easily followed in a stopped flow apparatus. This reaction was studied in the hemoglobin from the parasitic nematode Parascaris equorum, whose extremely high oxygen affinity is due to a very low dissociation rate. The rate of cyanide dissociation from ferrous Parascaris hemoglobin is not so dramatically different from that of other hemoglobins and myoglobins. Other features of the reaction are: (i) the rate constant of cyanide release is pH independent, an observation which is agreement with the possible absence of the distal histidine, given the mechanism suggested in a previous study (Bellelli, A., Antonini, G., Brunori, M, Springer, B.A. and Sligar, S.G. (1990) J. Biol. Chem. 265, 18898-18901), and (ii) the time-course shows no kinetic cooperativity. The structural basis of the extremely high oxygen affinity of Parascaris hemoglobin cannot be explained on the basis of the results here reported. This study also confirms that, even though cyanide binding to ferrous hemoglobins is controlled by distal interactions, the functional behaviour of this ligand is characteristic and differs from the behaviour of oxygen.

Allosteric Regulation↗
PubMed1996

Glucose uptake kinetics of Saccharomyces cerevisiae monitored with a newly developed FIA.

The glucose content of the culture liquid during shift experiments and synchronized cultures of Saccharomyces cerevisiae H1022 (ATCC 32167) was monitored using a greatly improved and highly precise FIA. During shift-up experiments on the dilution rate, an overshoot of the glucose-concentration was observed. The amplitude of the overshoot showed a dependency on the duration of undisturbed cultivation before application of the shift. Mutarotational non-equilibrium was excluded as the cause of the observed overshoot. For the first time glucose measurements of oscillating cultures of Saccharomyces cerevisiae are demonstrated with high accuracy and reproducibility. The data strongly support the proposals by Münch et al. (1992a, b) that faint oscillations in glucose concentration are responsible for the persistence of the synchronization. Analytical subsystems prove to be a powerful tool for investigation of the dynamics of metabolic pathways of microbial organisms. Accurate glucose measurements at low concentrations point out the limits and allow refinements of commonly used models.

Biological Transport, Active↗
PubMed1991

Flow injection immunoassay using a protein A immunoreactor.

Competitive immunoassays have been developed for the immunosuppressant cyclosporin A and the anti-asthmatic drug theophylline utilizing identical controlled pore glass-protein A microcolumns and flow injection techniques. For cyclosporin A the assay was based on a monoclonal antibody with fluorescence detection whilst for theophylline sheep antiserum and electrochemical detection was used.

Cyclosporine↗
PubMedDate not supplied

Spectrophotometric determination of promazine with an oxidative column in FIA manifolds.

A simple flow-injection spectrophotometric method for the determination of promazine is described. The two proposed procedures are based on the oxidation of analyte with a manganese dioxide column. Concentrations of promazine in the ranges 2-20 and 1-6 are determined with a relative standard deviation of 1.0%. The injection rates are 62 and 80 samples h-1, respectively. The influence of foreign species and the determination of promazine in a pharmaceutical formulation are also reported.

Calibration↗
PubMedDate not supplied

Liquid chromatographic separation of phenolic drugs using catalytic detection: comparison of an enzyme reactor and enzyme electrode.

A catalytic detection system based on the use of immobilized tyrosinase and two different transducers (photometric and electrochemical) is described. Comparison between tyrosinase immobilized in a packed-bed reactor and at the surface of a graphite electrode is discussed in terms of sensitivity in a flow injection system. The enzyme electrode configuration gives the highest sensitivity for the quantitation of dopamine. For the immobilized tyrosinase reactor with photometric detection the range for dopamine is linear up to 0.75 mM (136 micrograms ml-1) and the immobilized tyrosinase reactor with electrochemical detection and the tyrosinase electrode extends this dynamic range to 1 mM (181 micrograms ml-1). Liquid chromatographic separation and post-column detection using the tyrosinase electrode is shown for spiked samples of serum.

Biosensing Techniques↗
PubMed1991

Kinetic determination of aspartate aminotransferase in human serum with a flow-injection/multidetection system.

Photometric-kinetic methods for the determination of activity of aspartate aminotransferase are proposed. The flow-injection manifold used for this purpose includes a selecting valve which allows the sample to be trapped in a closed circuit where a solid reactor housing an auxiliary enzyme and a conventional single detector allows a multipeak recording to be obtained for each sample. This record represents a typical kinetic curve from which much information can be obtained to develop fixed-time and reaction-rate methods for the determination of the analyte based on its catalytic action on the L-aspartic acid-2 oxoglutarate system. The linear range is found to be between 1 and 500 U l-1, with relative standard deviation less than 1%. The utility of the methods is illustrated by the determination of the analyte in human serum from healthy and sick individuals.

Aspartate Aminotransferases↗