Selective Flow Injection Analysis Research Articles

An electrochemical in-vitro tool for study of in-vivo relevant biochemical oxidation/reduction of sulfide ion by human whole blood: Evidence for the biological detoxification of hydrogen sulfide

Studies related to redox reaction of human whole blood with hydrogen sulfide is highly important in biological system (e.g., detoxification of sulfide ion) and there have been several indirect experimental evidences for their interaction. This is the first and direct report for electrochemical oxidation and reduction of sulfide ion on a human whole blood chemically modified electrode system in physiological solution. A specific diffusion controlled electrochemical oxidation signal at 0V vs Ag/AgCl and reduction signal at −0.5V vs Ag/AgCl corresponding to the electrochemical conversion of sulfide ion to sulfate and sulfide to sulfur atom respectively by the Blood-Hemoglobin-FeIII/II redox site were noticed. These reactions are similar to the red blood cell functional behaviours with hydrogen sulfide (exist as HS− in a neutral solution) as detoxification mechanism in the human body. Control results of electrochemical sulfide oxidation/reduction reactions with commercial hemoglobin and heme derivative (hematin) modified electrodes support the observation. Calculated electrochemical sulfide oxidation parameters such as Tafel slope, transfer coefficient (α) and heterogeneous rate constant (Andrieux and Saveant model) values are 120mVdecade−1, 0.5 and 4.77±1.51×10−6mol−1cm3s−1 respectively. Selective flow injection analysis of sulfide ion (HS−) using the blood chemically modified electrode was demonstrated as a proof of concept for the applicability of the working electrode to analytical application.

MWCNT-chitosan composite chemically modified electrode as an electrochemical detector for highly selective flow injection analysis of H2O2

MWCNT-chitosan composite chemically modified electrode as an electrochemical detector for highly selective flow injection analysis of H2O2

Selective flow injection analysis of iodate in iodized table salts by riboflavin immobilized multiwalled carbon nanotubes chemically modified electrode

Riboflavin (vitamin B2) immobilized multiwalled carbon nanotubes modified electrode (GCE/MWCNT@RB) has been prepared and demonstrated as a selective and sensitive electrocatalytic flow injection analysis electrochemical sensor for iodate detection. The GCE/MWCNT@RB modified electrode showed a highly stable and well defined surface confined redox peak at an E1/2=155±20mV vs. Ag/AgCl with a surface excess value of 4.72nmolcm−2. Physicochemical and electrochemical characterizations reveal the presence of surface confined riboflavin sites on GCE/MWCNT system. At an applied potential=−0.1V vs Ag/AgCl, hydrodynamic flow rate=800μLmin−1 and phosphate buffer (pH 2) as a carrier solution condition, the analytical characteristics such as stability, repeatability, linear range and detection limit were described. The relative standard deviation of successive 29 injections of 25μM of iodate was 3.61%. Iodate calibration plot was linear in a range of 25–750μM with regression coefficient, sensitivity and limit of detection (S/N=3) of 0.9998, 0.77μAmM−1 and 2.7μmolL−1 (9.4ng/20μL) respectively. The new system showed absence of interference with iodide, chloride, nitrate, bromate and perchlorate. Quantitative detection of iodate in iodized table salts was further demonstrated.

Rapid and Sensitive Online Determination of Some Selective α1-Blockers by Flow Injection Analysis with Micelle-Enhanced Fluorescence Detection

A rapid, sensitive and selective flow injection analysis (FIA) method was developed for the determination of some selective α1-blockers including; terazosin (TER), doxazosin (DOX), prazosin (PRZ), and alfuzosin (ALF). The method was based on enhancement of the native fluorescence of the studied drugs in the presence of sodium dodecyl sulfate (SDS). The method was optimized for the buffer type, concentration and pH, surfactant type and concentration, flow rate and detection wavelengths in order to achieve the maximum sensitivity. The results showed that the best sensitivity was obtained by using SDS (10mM) in phosphate buffer (20mM, pH = 3), flow rate was 0.5ml/min and the detector was set at λex = 250 and λem = 389. Under these optimum conditions there was a linear relationship between the concentration and the fluorescence intensity in the range from 5-400ng ml(-) with correlation coefficient of more than 0.998. The detection and quantitation limits for the studied drugs by the proposed method were 3.2-11.9ng ml(-1) and 10.8-39.7ng ml(-1), respectively. The method was validated in accordance with the requirements of ICH guidelines and shown to be suitable for intended applications. Moreover, the binding constants for α1-blockers -SDS system were determined using the adduct model. The proposed method has been applied successfully for the analysis of the pure forms for studied drugs and also their pharmaceutical formulations and the results were compared with official methods.

Flow Injection Analysis of Hydrazine in the Aqueous Streams of Purex Process by Liquid Chromatography System Coupled with UV-Visible Detector

Present study describes the development of a rapid, sensitive and selective flow injection analysis of hydrazine in the aqueous streams of purex process by liquid chromatography system coupled with UV-Visible detector. The method is based on the formation of yellow coloured azine complex by reaction of hydrazine with para-dimethy laminobenzaldehyde (pDMAB). The formed yellow coloured complex is stable in acidic medium and has a maximum absorption at 460 nm. The presence of uranium in hydrazine solution is not interfering in the analysis. Under optimum condition, the absorption intensity linearly increased with the concentration of hydrazine in the range from 0.05-10 mg?L–1 with a correlation coefficient of R2=0.9999 (n=7). The experimental detection limit is 0.05mgL–1. The sampling frequency is 15 samples h–1 and the relative standard deviation was 2.1% for 0.05 mg?L–1. This method is suitable for automatic and continuous analysis and successfully applied to determine the concentration of hydrazine in the aqueous stream of nuclear fuel reprocessing.

Sensitive and selective flow-injection analysis coupled with solvent-extraction for the determination of pharmaceuticals and environmental pollutants

Sensitive and selective flow-injection analysis coupled with solvent-extraction for the determination of pharmaceuticals and environmental pollutants

Sensitive and selective flow injection analysis of hydrogen sulfite/sulfur dioxide by fluorescence detection with and without membrane separation by gas diffusion.

Highly sensitive and selective FIA flow injection analysis procedures for the determination of sulfite/hydrogen sulfite/sulfur dioxide were developed on the basis of an in situ-generated o-phthalaldehyde (OPA)/ammonium reagent and fluorescence detection. The highest sensitivity was achieved at an excitation wavelength of 330 nm, an emission wavelength of 390 nm, and at pH 6.5. Sulfite concentrations between 2.5 nM and 5 microM can be determined with relative standard deviations between 10.5 and 1.0% (n = 5, confidence level alpha = 0.05) by utilization of a reagent that contains 0.2 mM OPA and 0.4 M NH4Cl in 50 mM potassium phosphate buffer. A concentration of 0.1 mM sulfite can be selectively detected in the presence of thiosulfate, thioglycolate, tetrathionate, cysteine, and ascorbate. The fluorometric sulfite detection was combined with a membrane gas diffusion step to improve the selectivity with respect to nonvolatile fluorescing substances. The total sulfite content can be quantitatively separated as sulfur dioxide into an acceptor solution before its flow detection. Between 40 nM and 0.1 mM sulfite can be determined. After 1,000-fold dilution, the total sulfite content can be determined in white and red wines.

Zr(iv)‐spadns flow analysis procedure for determination of fluoride in surface and groundwater

A simple, fast and selective flow injection analysis (FIA) procedure for monitoring of fluoride in surface and ground water has been developed. The method is based on destruction of Zr(IV)‐SPADNS [2‐(p‐sulphophenylazo)1,8‐dihydroxynaphthalene‐3,6‐disulphonic acid trisodium salt] complex with fluoride ions in the presence of neutral surfactants i.e., TX‐100, TX‐300. The apparent molar absorptivity of the complex in term of fluoride lies in the range of (2.70‐ 5.20) × 103 Lmole‐1cm‐1 at absorption maximum 580 nm, depending upon acidity. The detection limit is 9 ppb F‐ at 4M HCl. The sample throughput is 80 samples/hr. Optimization of FIA variables and detailed studies of interferences of sulfate and phosphate with respect to acidity and sample volume injected were carried out. None of the tested ions interfere in the determination of F‐. The levels of fluoride pollution in the surface and groundwater of central India and their sources have been delineated.

Selective flow injection analysis of ultra-trace amounts of Cr(VI), preconcentration of it by solvent extraction, and determination by electrothermal atomic absorption spectrometry (ETAAS)

A rapid, robust, sensitive and selective time-based flow injection (FI) on-line solvent extraction system interfaced with electrothermal atomic absorption spectrometry (ETAAS) is described for analyzing ultra-trace amounts of Cr(VI). The sample is initially mixed on-line with isobutyl methyl ketone (IBMK). The Cr(VI) is complexed by reaction with ammonium pyrrolidine dithiocarbamate (APDC), and the non-charged Cr(VI)–PDC chelate formed is extracted into IBMK in a knotted reactor made from PTFE tubing. The organic extractant is separated from the aqueous phase by a gravity phase separator with a small conical cavity and delivered into a collector tube, from which 55 μl organic concentrate is subsequently introduced via an air flow into the graphite tube of the ETAAS instrument. The operations of the FI-system and the ETAAS detector are synchronously coupled. A significant advantage of the approach is that matrix constituents, such as high salt contents, effectively are eliminated. The extraction procedure was optimized by a simplex approach. A central composite design was subsequently employed to verify the estimated operational optimum. An 18-fold enhancement in sensitivity of Cr(VI) was achieved after preconcentration for 99 s at a sample flow rate of 5.5 ml min −1, as compared to direct introduction of 55 μl of sample, yielding a detection limit (3σ) of 3.3 ng l −1. The sampling frequency was 24.2 samples h −1. The proposed method was successfully evaluated by analyzing a NIST Cr(VI)-reference material, synthetic seawater and waste waters, and waste water samples from an incineration plant and a desulphurization plant, respectively.

Flow injection analysis of Zn and Co in beverages, biological, environmental and pharmaceutical samples

A new, simple, rapid and selective flow injection analysis (FIA) method for the spectrophotometric quantification (speciation of inorganic and organic form) of Zn and Co with ammonium thiocyanate and malachite green (MG) in the presence of surfactants (CPC and TX-100) is described. The value of apparent molar absorptivity of the Zn- and Co- complexes are (1.23) × 104 and (8.67) × 103 L mol–1cm–1 at absorption maximum, 635 nm, respectively. The detection limit (amount causing a peak height > 3 s) is 15 ppb Zn and 20 ppb Co, whereas their optimum working ranges for the quantitative determinations are 0.05–2.0 ppm Zn and 0.07–2.5 ppm Co in the real samples. The sample thoughput of the method is 120 samples/h at the flow rate of 5.0 mL/min with rel. std. dev. of < ± 1%. The method is free from interferences of almost all ions which are commonly associated with these metals in the complex materials. The composition of the complexes and their reaction mechanism involved are discussed. The effect of FIA and analytical variables for the determination of the metals are optimized. The method has been applied to the quantification of Zn and Co in beverages, biological, environmental, and pharmaceutical samples.

Novel chemiluminometric H 2O 2 sensors for the selective flow injection analysis

Hydrogen peroxide can be detected chemiluminometrically in the presence of luminol at cobalt and copper foils. The chemiluminescence signal can also be induced electrochemically. The linear determination ranges are 0.1–200 μM on cobalt and 5–2000 μM on copper under flow injection conditions. To improve the selectivity the chemiluminescence detector was combined with a thin layer gas dialysis cell. Hydrogen peroxide was detected in the range between 0.5 and 100 mM. The interference by a more than 100-fold excess of EDTA, α-ketocarboxylic acids and peroxodisulfate can be excluded. Peroxomonosulfate concentrations greater than a ten-fold excess of hydrogen peroxide cause a significant bias, which resulted from the hydrolysis of peroxomonosulfate.

Flow Injection-Spectrophotometric Determination of Trace Amounts of Iron with 2-Pyridyl-3′-sulfophenylmethanone 2-Pyrimidylhydrazone and Possibility of Sensitization by Analogue-Derivative Spectrophotometric Monitoring

A selective flow injection analysis (FIA) system has been proposed for the spectrophotometric determination of trace amounts of iron based on the 1:2 (metal:ligand) complex formation between iron(II) and 2-pyridyl-3′-sulfophenylmethanone 2-pyrimidylhydrazone(PSPmH). The system permits high throughput of 70 solutions per hour. The lower limit of determination is 10ppb of iron. The procedure has been applied successfully to the determination of iron in water samples. Possibility of further enhancement in the sensitivity in FIA by introducing analogue-derivative spectrophotometric monitoring is also suggested.