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Results for “Flow Injection Analysis”

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At least 1,747 records · Page 97Linked to original sources
PubMed1993

Flow injection chemiluminometric determination of epinephrine, norepinephrine, dopamine and L-dopa.

A method is proposed for the determination of 0.0500-1.00 microgram ml-1 of epinephrine and L-dopa and 0.100-1.00 micrograms ml-1 of norepinephrine and dopamine by their chemiluminogenic oxidation with potassium permanganate in acidic medium, in the presence of formaldehyde, which greatly improves the sensitivity. Flow injection allows the measurement of 80 solutions per hour. The method was also optimized for a continuous-flow system. Comparative results from numerous organic compounds proved the necessity for electron-donating groups on the benzene ring for sensitive chemiluminescent characteristics.

Dopamine↗
PubMed1993

Automated determination of peroxides in olive oil by flow injection.

A method for the determination of the peroxide value of olive oil based on flow injection principles is proposed. The method requires no pre-treatment of samples that have undergone natural or forced oxidation as the sensitivity can be accommodated over wide margins (determination range 3.4-537 mequiv kg-1). The precision of the method, expressed as relative standard deviation, ranges from 0.7 to 2.4% and the sampling frequency is 15 h-1.

Flow Injection Analysis↗
PubMed1993

Characterization of planar concentration gradients in a sequential-injection system for cell-perfusion studies.

This paper describes the characterization of a perfusion chamber that is coupled with a sequential-injection system and is being designed for live-cell perfusion. The apparatus consists of a multi-port valve, a peristaltic pump, a perfusion chamber and an epifluorescence microscope. The entire system is computer controlled and temperature regulated. The parameters discussed are the concentration-time profiles with regard to the volume of reagent used and the position of the cell in the perfusion chamber. Other parameters discussed include the stopped-flow compliance, reproducibility and symmetry of the concentration gradients formed. The system is shown to be suitable for two modes of perfusion; the first in which all cells are exposed to the same concentration of reagent, and the second in which cells are exposed to a gradient of concentrations. All characterization is performed with use of bulk fluorescein as a tracer, and a correlation is made between the bulk flow and the response within the cellular environment by using 5-[N-(octadecanoyl)amino]fluorescein.

Cells↗
PubMed1993

Simultaneous determination of ammonia nitrogen and L-glutamine in bioreactor media using flow injection.

A novel split stream flow injection (FI) system suitable for the simultaneous determination of L-glutamine and ammonia nitrogen (ammonia-N) in cell culture media is described. Potentiometric detection of ammonia-N in one portion of the manifold is achieved using a commercial ammonia gas-sensing electrode fitted with a wall-jet cap. L-Glutamine is quantified in the other part of the split sample by potentiometric detection of ammonium ions (by an ammonium-selective polymer membrane electrode), liberated from the hydrolysis of glutamine after the sample flows through a glass bead reactor containing immobilized glutaminase. Endogenous ammonia-N and potassium ions that would normally interfere with the glutamine measurement are removed upstream using a unique tubular cation-exchange unit. Using 50 microliters sample volumes and mixed solutions of ammonium chloride and L-glutamine in Iscove's Modified Dulbecco's Medium to calibrate the FI measuring system, values for ammonia-N and L-glutamine determined for 22 media samples obtained from a bioreactor growing retroviral producer cells correlate well with those measured with commercial, manual enzymic-spectrophotometric assay kits.

Ammonia↗
PubMed1993

Trace metal determination in tears by anodic stripping voltammetry in a capillary flow injection system.

The adaptation of a fused silica capillary system to flow injection is described. The incorporated electrochemical cell, consisting of a microelectrode arrangement, is demonstrated to be well suited for conductivity and voltammetric measurements. Microanalytical studies with injection volumes within the nanolitre range were performed. Analytical characteristics of the method, such as accuracy, precision, sensitivity and limit of detection, are discussed. By using capillary flow injection, tear samples were investigated with respect to conductivity and trace-metal concentration. The last was performed via anodic stripping voltammetry at mercury-coated platinum microdisc electrodes. Lead, cadmium and copper were found to be present at concentrations in the lower microgram l-1 range.

Child↗
PubMed1994

Discovering flow injection: journey from sample to a live cell and from solution to suspension.

Twenty years after its inception, flow injection is seen as an ever-expanding method, as new modifications are discovered such as flow injection cytoanalysis and the flow injection on renewable surfaces technique. In this review, a personal view of the future rather than the history of flow injection is given, with comment on how research is actually being conducted.

Cytological Techniques↗
PubMed1994

Flow injection spectrophotometric determination of aspartame in dietary products.

A flow injection spectrophotometric method has been developed for the determination of aspartame in dietary products using ninhydrin as a colorimetric reagent. The reaction was conducted in a 1 + 1 v/v methanol-isopropanol medium also containing potassium hydroxide. The absorbance measurements were made at 603 nm. The results obtained for the determination of aspartame in table sweetener, pudding, gelatin, and refreshment (i.e., a powder dissolved in water for drinking) are in good agreement with the results obtained using a conventional manual procedure (correlation coefficient, r = 0.9984). Thirty-six results were obtained per hour, and the relative standard deviation was less than 3.5% (n = 6) for all samples. The detection limit (three times the signal blank/slope) was 3.8 x 10(-5) mol l-1 of aspartame.

Aspartame↗
PubMed1995

Simultaneous determination of copper and zinc in the hair of children by pH gradient construction in a flow-injection system.

A flow-injection method is described for the simultaneous determination of copper and zinc with a single detector using the pH gradient technique. Zincon is used as the colour reagent for the spectrophotometric determination. The linear range for the determination of zinc is 0.4-12 micrograms ml-1 and for copper is 0.1-3.0 micrograms ml-1. About 20-30 samples can be determined in one hour. The proposed method has been applied to the determination of zinc and copper in childrens' hair.

Child↗
PubMed1995

Determination of substrates using poly(ethylene glycol)-stabilized dehydrogenase enzymes by microlitre per minute flow injection.

Flow injection (FI), at a flow rate of microliter min-1, is an effective method for enzymic substrate determination using low concentrations of poly(ethylene glycol) (PEG)-stabilized soluble enzymes. PEG stabilizes dehydrogenase enzymes for at least several days by promoting sub-unit association. Band broadening of knitted open tubular reactors is reduced as flow rate decreases below 300 microliter min-1 and a small tubing diameter is important for a faster rate of absorbance signal increase with residence time. Small (0.5 microliter) sample injections also ensure narrow FI peaks. The determination of several substrates such as pyruvate, lactate, and cortisone using appropriate PEG-stabilized enzymes is demonstrated with this FI instrument at 25 or 50 microliters min-1 with sample throughputs of the order of 2-3 min per sample. The determination of lactate in serum samples is also possible. The advantage of this method, sample throughput, is not sacrificed but enzyme consumption is considerably less, compared to standard ml min-1 FI.

Animals↗
PubMed1995

Automated determination of microbial peroxidase activity in fermentation samples using hydrogen peroxide as the substrate and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) as the electron donor in a flow injection system.

An automated flow injection method has been developed for the determination of microbial peroxidase activity. The substrate used was hydrogen peroxide and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate (ABTS) was used as the electron donor. In the presence of hydrogen peroxide, peroxidase catalyses the dehydrogenation of ABTS, resulting in the formation of a resonance-stabilized radical cation of ABTS. The green-blue colour formed, recorded at 418 nm, is taken as a measure of the peroxidase activity. The general technical conditions and the general enzymic kinetics have been optimized. Conditions for activation and stabilization of the enzyme were found, e.g., ammonium sulfate acts as a peroxidase activator. The resulting method has a good precision, sensitivity and speed.

Autoanalysis↗
PubMed1995

Flow injection spectrofluorimetric method for the determination of magnesium in blood serum.

A flow injection configuration for the spectrofluorimetric determination of magnesium is proposed. The method is based on the formation of a strongly fluorescent complex of magnesium ion with 2-hydroxy-1-naphthaldehyde salicyloylhydrazone in alkaline, aqueous-ethanolic (50% v/v) solutions. The optimal chemical conditions for complex formation in the mixed solvent were studied and the flow injection manifold was optimized and used for the determination of magnesium in 1000-fold diluted serum samples without any other pre-treatment. The measurement throughput was 120 h-1. The detection limit of the method was 2 micrograms l-1 (2 mg l-1 for serum). The concentration range of application is 4.8-120 micrograms l-1 (0.2-5.0 mumol l-1). Within-run relative standard deviations for the method at 4.8, 24 and 120 micrograms l-1 of magnesium were 3.5, 1.2 and 0.7%, respectively. Analytical recoveries range from 96.2 to 102% (mean 98.8%).

Drug Stability↗
PubMed1996

Flow injection microscopy: a novel tool for the study of cellular response and drug discovery.

Studying responses of live cells to agonists, antagonists and other physical stimuli offers insight into their complex membrane and internal biochemistry. An experimental technique has been developed in which responses of living cells in an inverted radial flow chamber are continuously monitored while being repeatedly stimulated using controlled pulses of a biologically active ligand. Precisely defined flow conditions result in reproducible peaks which can be numerically analysed by comparison with a tracer curve obtained by substituting a dye for the stimulus. Exploratory studies have demonstrated that the flow injection technique can provide a novel method for kinetics of receptor binding and cellular responses. Flow injection microscopy (FIM) allows identification of biologically active ligands and their ranking based on measurement of the cellular responses in a short time frame. The use of FIM for rapid drug screening, through monitoring of the initial kinetics of cellular responses, is demonstrated on a model system.

Cell Line↗
PubMed1996

Simultaneous assay of nitrite, nitrate and chloride in meat products by flow injection.

A flow injection (FI) analytical method for the simultaneous assay of nitrite, nitrate and chloride in meat products is reported. The method is based on the potentiometric determination of chloride using a tubular ISE and on the spectrophotometric determination of nitrite. The FI system consisted in splitting the flow after potentiometric detection using a tubular detector and the subsequent confluence of the flow before reaching the spectrophotometric detector. This allowed the reduction of nitrate to nitrite in part of the sample plug on an on-line copper cadmium reductor column. Since each channel had a different residence time, two peaks were obtained for nitrite and nitrite plus nitrate. Spectrophotometric determination was made after a diazotization-coupling reaction. The results obtained were in good agreement with reference procedures and showed adequate precision (RSDs less than 6% for chloride and nitrite and 2% for nitrate). A high sampling rate was obtained (120 determinations per hour corresponding to 40 samples per hour).

Chlorides↗
PubMed2000

Flow injection-pulse amperometric detection of ephedrine at a cobalt phthalocyanine modified carbon paste electrode.

Direct detection of ephedrines and other underivatized amino compounds (amines, alicyclic amines, alkanolamines, and amino acids) can be carried out via electrocatalytic oxidation at a carbon paste electrode (CPE) modified with cobalt phthalocyanine (CoPC) in alkaline solution (0.10 mol L-1 NaOH). Most of the amino compounds tested could be determined using the CoPC/CPE in an amperometric flow detector. The analytical signal of ephedrine was stabilised by alternating the potential between an anodic detection potential of +0.30 V (+0.45 V for other amino compounds) applied for 220 ms and a cathodic reactivation potential of -0.30 V applied for 100 ms (potentials versus SCE). The linear response range for ephedrine was within 1-100 mumol L-1 and the detection limit was 0.8 mumol L-1 with a 100 microL sample loop and a typical sampling ra 60 h-1. The signal (oxidation peak current) reproducibility was 2-3%. The method was applied to the determination of ephedrine in pharmaceutical formulations with results comparable to those obtained with a standard spectrophotometric method.

Carbon↗
PubMed2000

Chemiluminometric determination of reserpine and related alkaloids.

The determination of the alkaloids reserpine, rescinnamine and yohimbine based on a chemiluminogenic reaction with potassium permanganate in the presence of polyphosphoric acid is described. The investigation was carried out using a batch and a flow injection chemiluminometer. Both approaches were accurate and precise, allowing the measurement of reserpine within the ranges 0.100-3.00 and 0.050-3.00 micrograms ml-1 with RSD values for 1.00 microgram ml-1 of 1.91 and 0.33% (n = 8) with the batch and the flow injection manifold, respectively. The procedure was successfully applied to formulations after extraction of reserpine with chloroform, with recoveries from commercial formulations within the range 95.2-99.0%.

Adrenergic alpha-Antagonists↗
PubMed2000

Dual analyte flow injection fluorescence immunoassays using thiophilic gel reactors and synchronous scanning detection.

Heterogeneous fluorescence immunoassays have been automated using flow injection manifolds incorporating thiophilic gel solid phase reactors to separate antibody-bound and unbound analyte molecules. Antibody elution is achieved by changes in ionic strength, thus allowing the use of pH sensitive fluorescent labels. This facilitates the development of dual analyte systems, in which two competitive immunoassays with separate labels are monitored in parallel. Detection of the fluorophores by high speed synchronous fluorescence scanning while the flow is briefly stopped utilises either one synchronous interval which detects both fluorophores, or two separate scans at different wavelength intervals, one for each fluorophore. Simultaneous analyses of serum albumin and transferrin exemplify these novel approaches. Spectroscopic interferences are very small, analyte recoveries are close to 100%, with a relative standard deviation of 5-6% and a sampling rate of 20 h-1.

Animals↗