Flow‐Injection Pulsed‐Amperometric Determination of Free Glycerol in Biodiesel at a Gold Electrode

This work reports the highly‐sensitive amperometric determination of free glycerol in biodiesel at a gold electrode adapted in a flow‐injection analysis (FIA) cell. The amperometric method involved the continuous application of three sequential pulses to the working electrode (+250 mV, +700 mV, and ?200 mV, for 100 ms each). This sequence of potential pulses eliminated electrode passivation and dramatically increased the analytical signal. The proposed FIA‐amperometric method presented low relative standard deviation between injections (1.5 %, n=15), high analytical frequency (85 h^?1), satisfactory recovery values (93–118 %) for spiked samples, wide linear range (from 1 to 300 µmol L^?1), and low detection limit (0.5 µmol L^?1).     

Applications of Amperometric Silica Sol-Gel Modified Enzyme Biosensors

ABSTRACT

The applications of amperometric sol-gel modified enzyme biosensors in numerous analyses of clinical, industrial and environmental importance have been demonstrated. Certain biosensors have been employed as the sensor in a FIA amperometric detector. The results obtained by the biosensors generally corroborate well with the classical or official method. In many cases, the recovery results obtained by the biosensor have been satisfactory.     

Amperometric determination of hydrogen peroxide with a manganese dioxide film-modified screen printed carbon electrode

A carbon thick film electrode modified with an MnO₂-film is investigated as an amperometric detector for hydrogen peroxide in flow-injection analysis (FIA). At an operating potential of +0.48 V vs. Ag/AgCl catalytic oxidation of the analyte is exploited for amperometric monitoring. Experimental parameters, such as pH of the carrier, working potential, flow rate and injection volume, are optimized. The amperometric signals are linearly proportional to the concentration of H₂O₂ in the range from 0.005 to 10 mg/L, showing a detection limit (3σ) of 2.3 μg/L. The method is applied to the determination of H₂O₂ in rain water and to a simple assay to quantify glucose in human plasma.     

A Novel Thin‐Film Copper Array Based on an Organic/Inorganic Sensor Hybrid: Microfabrication,Potentiometric Characterization,and Flow‐Injection Analysis Application

A first step towards the microfabrication of a thin‐film array based on an organic/inorganic sensor hybrid has been realized. The inorganic microsensor part incorporates a sensor membrane based on a chalcogenide glass material (Cu‐Ag‐As‐Se) prepared by pulsed laser deposition technique (PLD) combined with an PVC organic membrane‐based organic microsensor part that includes an o‐xylyene bis(N,N‐diisobutyl‐dithiocarbamate) ionophore. Both types of materials have been electrochemically evaluated as sensing materials for copper(II) ions. The integrated hybrid sensor array based on these sensing materials provides a linear Nernstian response covering the range 1×10^?6–1×10^?1 mol L^?1 of copper(II) ion concentration with a fast, reliable and reproducible response. The merit offered by the new type of thin‐film hybrid array includes the high selectivity feature of the organic membrane‐based thin‐film microsensor part in addition to the high stability of the inorganic thin‐film microsensor part. Moreover, the thin‐film sensor hybrid has been successfully applied in flow‐injection analysis (FIA) for the determination of copper(II) ions using a miniaturized home‐made flow‐through cell. Realization of the organic/inorganic thin‐film sensor hybrid array facilitates the development of a promising sophisticated electronic tongue for recognition and classification of various liquid media.     

Amperometric determination of hydrogen peroxide with a manganese dioxide film-modified screen printed carbon electrode

A carbon thick film electrode modified with an MnO₂-film is investigated as an amperometric detector for hydrogen peroxide in flow-injection analysis (FIA). At an operating potential of +0.48 V vs. Ag/AgCl catalytic oxidation of the analyte is exploited for amperometric monitoring. Experimental parameters, such as pH of the carrier, working potential, flow rate and injection volume, are optimized. The amperometric signals are linearly proportional to the concentration of H₂O₂ in the range from 0.005 to 10 mg/L, showing a detection limit (3σ) of 2.3 μg/L. The method is applied to the determination of H₂O₂ in rain water and to a simple assay to quantify glucose in human plasma. Received: 29 January 1998 / Revised: 4 May 1998 / Accepted: 13 May 1998     

Ruthenium Oxide Hexacyanoferrate Modified Electrode for Hydrogen Peroxide Detection

A sensor for H₂O₂ amperometric detection based on a Prussian blue (PB) analogue was developed. The electrocatalytic process allows the determination of hydrogen peroxide at 0.0 V with a limit of detection of 1.3 μmol L^?1 in a flow injection analysis (FIA) configuration. Studies on the optimization of the FIA parameters were performed and under optimal FIA operational conditions the linear response of the method was extended up to 500 μmol L^?1 hydrogen peroxide with good stability. The possibility of using the developed sensor in medium containing sodium ions and the increased operational stability constitute advantages in comparison with PB‐based amperometric sensors. The usefulness of the methodology was demonstrated by addition‐recovery experiments with rainwater samples and values were in the 98.8 to 103% range.     

Simple and Fast Determination of Warfarin in Pharmaceutical Samples Using Boron‐doped Diamond Electrode in BIA and FIA Systems with Multiple Pulse Amperometric Detection

This paper proposes the use of the boron‐doped diamond electrode (BDDE) in flow and batch injection analysis (FIA and BIA) systems with multiple‐pulse amperometric (MPA) detection for the determination of warfarin (WA) in pharmaceutical formulations. The electrochemical behavior of WA obtained by cyclic voltammetry (CV) in 0.1 mol L⁻¹ phosphate buffer shows an irreversible oxidation process at +1.0 V (vs Ag/AgCl). The MPA was based on the application of two sequential potential pulses as a function of time on BDDE: (1) for WA detection at +1.2 V/100 ms and; (2) for electrode surface cleaning at −0.2 V/200 ms. Both hydrodynamic systems (FIA‐MPA and BIA‐MPA) used for WA determination achieved high precision (with relative standard deviations around 2 %, n =10), wide linear range (2.0−400.0 μmol L⁻¹), low limits of detection (0.5 μmol L⁻¹) and good analytical frequency (94 h⁻¹ for FIA and 130 h⁻¹ for BIA). The WA determination made by the proposed methods was compared to the official spectrophotometric method. The FIA‐MPA and BIA‐MPA methods are simple and fast, being an attractive option for WA routine analysis in pharmaceutical industries.     

Internal standard in flow injection analysis with amperometric detection

In this work, we describe for the first time the use of the internal standard method in flow injection analysis (FIA) with amperometric detection. The method is based on the application of sequential potential pulses to the working electrode in an electrochemical flow cell. The sequence of potential pulses is selected in such a way that the analyte and internal standard compound are detected and monitored individually and independently at the same working electrode. This approach compensates for random errors associated with variations of flow rate, injection volume, ionic strength difference between standards and samples, and accidental insertion or formation of air bubbles in the carrier stream. In addition, this method can overcome the major drawback of amperometric detection using solid electrodes, which is gradual electrode passivation. To illustrate the potential of this method, the flow-injection amperometric detection of uric acid using [Fe(CN)₆]^3? as an internal standard (IS) is presented as an example.     

Batch‐injection versus Flow‐injection Analysis Using Screen‐printed Electrodes: Determination of Ciprofloxacin in Pharmaceutical Formulations

This article highlights the potential use of multi‐walled carbon‐nanotube modified screen‐printed electrodes (SPEs) for the amperometric sensing of ciprofloxacin and compares the association of batch‐injection analysis (BIA) and flow‐injection analysis (FIA) with amperometric detection. Both analytical systems provided precise (RSD<5 %) and sensitive determination of ciprofloxacin (LOD<0.1 μmol L^?1) within wide linear range (up to 200 μmol L^?1). Accuracy of both methods was attested by recovery values (93–107 %) and comparison with capillary electrophoresis. The BIA system is completely portable (especially due to association with SPEs) and provided faster analyses (130 h^?1) and more sensitive detection than the FIA system due to the higher flow rates of injection.     

Flow Injection Photoamperometric Investigation of Ascorbic Acid Using Methylene Blue Immobilized on Titanium Phosphate

Abstract

Methylene blue (MB) was incorporated into titanium phosphate (TiP) after pretreatment of TiP with the gas, n‐butyl amine. The dye is strongly retained and not easily leached from the layered host matrix. The adsorbed MB on TiP was used to prepare modified carbon paste electrodes (MCPE), which were studied voltammetrically and in amperometric flow injection (FI) mode for the electrocatalytic oxidation of ascorbic acid (AA). The electrochemical behavior of the immobilized dye was investigated with cyclic voltammetry, at a pH 7.0 phosphate buffer containing 0.5 M KCl, at different potential scan rates. The MB immobilized on the support underwent a quasi‐reversible electrochemical redox reaction. A homemade flow‐through electrochemical cell with a suitable transparent window for irradiation of the electrode surface was constructed and used for amperometric FI studies. The photoamperometric‐FI conditions were optimized for sensitivity and reproducibility at a flow rate of 1.5 mL/min, a transmission tubing length of 25 cm, a sample injection volume of 100 µL, and a constant applied potential of +100 mV vs. SCE. The calibration curve for AA was linear over the concentration range from 1.0×10^?6 to 2.5×10^?5 mol l^?1 for both amperometric and photoamperometric studies. But the slope of the photoelectrocatalytic FIA procedure was improved about 52% compared with those obtained without irradiation. The results obtained for AA determination in some pharmaceutical products are in good agreement with those obtained using the procedure involving the reaction between triiodide and AA.     

A Simple Strategy for Simultaneous Determination of Paracetamol and Caffeine Using Flow Injection Analysis with Multiple Pulse Amperometric Detection

In this work, we report a simple and novel strategy for simultaneous analysis using flow injection analysis with multiple pulse amperometric (FIA‐MPA) detection. The proposed strategy was successfully used for simultaneous determination of paracetamol and caffeine (model analytes) in pharmaceutical formulations. A sequence of potential pulses (waveform) was selected in such a way that PA is selectively oxidized at E₁ (+1.20 V/50 ms) and both compounds (PA+CA) are simultaneously oxidized at E₂ (+1.55 V/50 ms); hence, current subtraction (using a correction factor) can be used for the selective determination of CA. The proposed FIA method is simple, cheap, fast (140 injections h^?1), and present selectivity for the determination of both compounds in pharmaceutical samples, with results similar to those obtained by HPLC at a 95 % confidence level.     

Microfluidic Setup for Simultaneous Separation and Electrochemical Determination of Hg2+ and Ag+ Ions in Water

Here is presented a setup made of a combination of an injection valve, a hand-made chromatographic microcolumn and an electrochemical detector for the simultaneous separation of Hg²⁺ and Ag⁺ ions in water. The microcolumns were packed with exchanger resin and used for the separation of Hg²⁺ and Ag⁺ ions, whereas a screen-printed carbon electrode (SPCE) was the amperometric detector. The performances of the SPCE towards ions were firstly studied in a FIA setup. The efficiency of ion separation was then evaluated. The reproducibility, stability, and the regeneration of the obtained microcolumns were also studied and discussed.     

Novel Amperometric Sensor Based on Rigid Near‐Percolation Composite

A novel amperometric sensor based on a rigid graphite‐epoxy composite of which composition is near to the percolation is reported. The electrochemical response of the novel transducer material was evaluated in terms of reproducibility of the fabrication process and reproducibility and repeatability of the analytical signal. The signal to noise ratio was improved. atomic force microscopy (AFM) technique was used to obtain qualitatively information. Amperometric detection of chlorine in water was carried on at a set potential of ?250 mV vs. Ag/AgCl. The developed flow injection analysis (FIA) system responded linearly to chlorine concentration between 0.15 mg L^?1 and 4 mg L^?1with a sensitivity of ?0.20 μA L mg^?1. The proposed system was applied to real samples from swimming‐pool water. No significant difference was observed regarding the standard method.     

Homogeneous Amperometric Immunoassay for Digoxin

Abstract

A homogeneous spectrophotometric EMIT immunoassay for the measurement of digoxin has been converted to an amperometric immunoassay format capable of analysing digoxin in diluted serum. NADH produced by glucose-6-phosphate dehydrogenase (G6PDH) labelled digoxin was detected amperometrically by its rapid, efficient oxidation at platinized activated carbon electrodes (PACE) poised at +150 mV vs Ag/AgCl. The new amperometric procedure resulted in a simplified assay protocol with a decreased overall assay time, enhanced NADH detection and minimal sample pretreatment.     

Electroimmobilization of MAO into a Polypyrrole Film and Its Utilization for Amperometric Flow Detection of Antidepressant Drugs

The preparation of a biosensor based on the enzymatic immobilization in polypyrrole polymer for the detection of antidepressant drugs is described. The enzyme monoamine oxidase (MAO) was immobilized by electropolymerization of pyrrole around a platinum electrode, at a constant potential of +0.75 V (vs. Ag/AgCl) in such a way to obtain a membrane thickness, which was constant and equal to 100 mC/cm². The biosensor was obtained from a 0.1 M KCl saline solution containing pyrrole at a concentration equal to 0.4 M and 2.5 mU/mL of MAO. The biosensor was adapted to a continuous flow injection analysis system (FIA) with the amperometric detection of hydrogen peroxide produced by enzymatic reaction carried out at a potential of +0.7 V (vs. Ag/AgCl), pH 7.4 and temperature of 37 °C. In optimized flow conditions, the biosensor presented an analytical response for fluoxetine in the interval between 0.67 and 4.33 mM, with a detection limit of 0.10 mM. The analytical use of the biosensor developed was evaluated through analysis of commercial pharmaceutical products containing fluoxetine, available on the Portuguese market. The amperometric flow results obtained do not differ significantly from the values resulting from analysis of the same products by the method proposed by the US Pharmacopeia, with sampling rates of 20–25 samples/hour.     

Electroanalytical Study of the Pesticide Asulam

The electrochemical behaviour of the herbicide Asulam was studied by cyclic and square wave voltammetry. Asulam may be irreversibly oxidised at a glassy carbon electrode. Maximum currents were obtained at pH = 1.9 in aqueous electrolyte solution. Based on the electrochemical behaviour of Asulam, two analytical methodologies were developed for its determination in water samples, using square wave voltammetry (SWV) and flow injection analysis (FIA) coupled with an amperometric detector. Limits of detection of 7.1 2 10 m 6 mol L m 1 and 1.2 2 10 m 8 mol L m 1 for SWV and FIA respectively, were achieved. Repeatability was calculated by assessing the relative standard deviation (%) for 10 consecutive determinations of one sample. The found values were 2.1% for SWV and 5.0% for FIA. Validation of the results provided by SWV and FIA methodologies was performed by comparison with results from an HPLC-DAD technique. Good relative deviations were found (< 5%). Recovery trials were performed to assess the accuracy of the results and the obtained values were between 84% and 107% for both methods.     

Development of an FIA system with amperometric detection for determination of bentazone in estuarine waters

On the basis of its electrochemical behaviour a new flow-injection analysis (FIA) method with amperometric detection has been developed for quantification of the herbicide bentazone (BTZ) in estuarine waters. Standard solutions and samples (200 microL) were injected into a water carrier stream and both pH and ionic strength were automatically adjusted inside the manifold. Optimization of critical FIA conditions indicated that the best analytical results were obtained at an oxidation potential of 1.10 V, pH 4.5, and an overall flow-rate of 2.4 mL min(-1). Analysis of real samples was performed by means of calibration curves over the concentration range 2.5x10(-6) to 5.0x10(-5) mol L(-1), and results were compared with those obtained by use of an independent method (HPLC). The accuracy of the amperometric determinations was ascertained; errors relative to the comparison method were below 4% and sampling rates were approximately 100 samples h(-1). The repeatability of the proposed method was calculated by assessing the relative standard deviation (%) of ten consecutive determinations of one sample; the value obtained was 2.1%.     

Amperometric Immunosensor for the Determination of 2′,3′-dideoxyinosine

Abstract

An amperometric immunosensor, based on carbon paste impregnated with solubilized antidideoxyinosine (from rabbit lyophilized powder, whole antiserum) has been constructed for the assay of anti-HIV agent dideoxyinosine (didanosine, DDI). The amperometric immunosensor was reliably used for dideoxyinosine assay in the 900 pmol/L to 9 nmol/L concentration range, with a detection limit of 180 pmol/L, at E = +1.04 V vs. Ag/AgCl. The construction of the immunosensor is reproducible. Its surface can be easily renewed by simple polishing on an aluminium paper. The new amperometric immunosensor is reliable for the assay of 2′,3′-dideoxyinosine in raw material as well as in its pharmaceutical formulation (Videx tablets).     

An improved FIA biosensor for the determination of aspartame in dietary food products

A flow injection analysis (FIA) biosensor system was developed for the determination of the artificial sweetener aspartame (l-aspartyl-l-phenylalanine methyl ester). The system consisted of an enzyme column of pronase immobilized on activated arylamine glass beads and al-amino acid oxidase electrode connected in series. The dipeptide bond of aspartame was cleaved by immobilized pronase to release phenylalanine, which was in turn monitored by the enzyme electrode that usedl-amino acid oxidase, immobilized on a preactivated nylon membrane in combination with an amperometric electrode (platinum vs silver/silver chloride, 700 mV). The response of the FIA biosensor was linear up to 1 mM aspartame with a lower detection limit of 25 μM and had good reproducibility (rsd 0.3%). The FIA biosensor was stable for at least 30 h of continuous use atT _r .Each assay takes 4 min giving a sample throughput of 15 h^?1 When applied to aspartame in dietary food products the results obtained agreed well with those reported by the product manufacturers.     

Flow injection,amperometric determination of ethanol in wines after solid-phase extraction

Ethanol in wines was determined by flow injection analysis with an amperometric detector using an oxidized nickel wire. Solid-phase extraction with a strong anion exchanger was used to remove interferences such as organic acids from the matrix, and the residue of the extraction was injected directly into the FIA system. The recoveries of ethanol from wines spiked with standards ranged from 101% to 103%. The response of the nickel electrode to ethanol is dependent on the applied potential and the pH of the carrier. The optimal conditions for the detection of ethanol were an applied potential of +0.60 V (vs. Ag/AgCl) in a carrier of 100 mM sodium hydroxide solution. The electrode exhibited a linear response from 10⁻⁵ to 10⁻³ M, with a detection limit of 1 × 10⁻⁶ M. The method was demonstrated by the determination of ethanol in wines.