Flow Injection Analysis Detection Research Articles

Voltammetric Detection of Ascorbic Acid at Organic Conducting Polymers Electrodes and Flow Injection Analysis

In this paper, a sensitive and rapid modified electrode for the determination of Ascorbic Acid (AA) is proposed. In this study, active compound AA was determined from commercial drug form based on electrochemical oxidation properties at various conducting polymer electrodes by voltammetric methods. Electrodes modified by the electrodeposition of conducting organic polymers such as poly(3-methylthiophene, PMT), polypyrrole (PPY) and polyaniline (PAN) were used as chemical sensors for voltammetric analysis and flow injection detection of AA. The electrochemical behavior of AA at conducting polymer electrodes was compared and the effects on behavior of electrolyte type and its pH and the film thickness were systematically examined. The results showed that the proposed modified surface catalyzes the oxidation of AA. Electrocatalytic efficiency decreases in order of PMT > PPY > PAN. Voltammetric peak positions were affected by the nature of the electrolyte and its pH. Also, the effect of increasing film thickness was to observe increased peak heights for oxidation potential of AA. The best results for the determination of AA were obtained by DPV in Na2SO4 (pH 2.0) and PMT electrodes. Polymer coated electrodes were also used in an amperometric detector for flow injection analysis of AA. The responses of the polymer electrode were 5–15 times larger as compared to those of bare platinum. PMT showed improved performance as an amperometric detector for flow injection analysis systems over other types of polymer electrodes. Detection limits as low as 1×10−9 M were achieved using the PMT, compared to 1×10−6 M using platinum electrodes.

Novel dual-sensor for creatinine and 8-hydroxy-2'-deoxyguanosine using carbon-paste electrode modified with molecularly imprinted polymers and multiple-pulse amperometry

Abstract We present a novel amperometric dual-imprinted sensor for simultaneous determination of creatinine (Cre) and 8-hydroxy-2′-deoxyguanosine (8-OHdG) in human urine and serum. The sensor used multiple-pulse amperometric detection in flow injection analysis (MPA-FIA). Copper oxide nanoparticles were coated with the Cre molecularly-imprinted polymer (CuO@MIP), using methacrylic acid as the functional monomer and N, N′-(1,2-dihydroxyethylene) bis-acrylamide as cross-linker. For 8-OHdG sensing, we embedded platinum nanoparticles in reduced graphene oxide and then coated it with guanosine poly-dopamine MIP (PtNPs-rGO@MIP). A carbon-paste electrode (CPE) was then formed containing both nanocomposites to give the dual MIP sensor (CuO@MIP and PtNPs-rGO@MIP/CPE). We developed a dual-potential waveform as a function of time, with Edet.1 (+0.4 V/150 ms) to determine Cre selectively and Edet.2 (+0.6 V/250 ms) to analyze both compounds simultaneously (Cre and 8-OHdG). Subtracting the two signals at 0.6 V and 0.4 V (using a correction factor), respectively, from each other allowed for quantifying 8-OHdG without interference from Cre. The MIP sensor has a linear range of 0.5–150 μM for creatinine and 0.005–50 μM for 8-OHdG, with limits of detection in nano-molar level. The proposed method is successfully applied for the simultaneous determination of Cre and 8-OHdG in urine and serum samples.

Analytical Capabilities of Coulometric Sensor Systems in the Antioxidants Analysis

The definition of antioxidants (AOs), their classification and properties as well as electrochemical sensor systems for AOs analysis are briefly discussed. The analytical capabilities of coulometric titration with electrogenerated titrants as sensor systems for AOs determination have been considered in detail. The attention focused on the individual AO quantification that was mainly used in the pharmaceutical analysis and estimation of total antioxidant parameters (total antioxidant capacity (TAC), ferric reducing power (FRP) and ceric reducing/antioxidant capacity (CRAC)) allowing the fast screening of the target samples including their quality control. The main advantages of coulometric sensor systems are pointed out. The selective quantification of individual AO in a complex matrix using a combination of chromatography with coulometric or coulometric array detection under potentiostatic mode is discussed. The future development of coulometric sensor systems for AOs analysis is focused on the application of novel coulometric titrants and the application of coulometric detection in flow injection analysis.

A Review: Square Wave Adsorptive Stripping Voltammetry Determination ofPesticide and Ultra-trace Inorganic Ions in Environmental Samples

Environmental pollution caused by pesticides and ultra-trace amounts of inorganic ions in the different environmental samples has become an issue of serious concern in the last years. Thus, the development of novel, simple, fast, sensitive, and cheap methods for the detection of pesticide residues and ultra-trace inorganic ions in the environmental sample is very significant task now days. The SWAdSV can be conjuncted with different modified electrode such as SWAdSV with modified Hanging mercury drop electrode, SWAdSV with multi-walled carbon nanotube paste electrode, SWAdSV with boron-doped diamond electrode, SWAdSV with flow-injection analysis detection and etc. SWAdSV can be used to perform an experiment much faster than normal and differential pulse techniques, which typically run at scan rates of 1 to 10 mV/sec. Square wave voltammetry employs scan rates up to 1 V/sec or faster, allowing much faster determinations. A typical experiment requiring three minutes by normal or differential pulse techniques can be performed in a matter of seconds by square wave voltammetry. The aim of the review was the use of square wave adsorptive stripping voltammetry in conjunction with different modified electrode for the determination of pesticide and ultra-trace inorganic ions in environmental samples.

Investigation of the Electrochemical Behavior of Hydroquinone at Some Conducting Polymer Electrodes and Amperometric Detection

In this paper, a rapid and sensitive modified electrode for the determination of hydroquinone (HQ) is proposed. In this study, active compound HQ was determined from commercial drug form based on electrochemical oxidation properties at various electrodes by voltammetric methods. Electrodes modified by the electrodeposition of conducting organic polymers such as poly(3-methylthiophene, PMT), polypyrrole (PPY) and polyaniline (PAN) were used as chemical sensors for voltammetric analysis and flow injection detection of HQ. The electrochemical behavior of HQ at conducting polymer electrodes was compared and the effects on behavior of electrolyte type and its pH and the film thickness were systematically examined. The results showed that the proposed modified surface catalyzes the oxidation of HQ. Electrocatalytic efficiency decreases in order of PMT > PPY > PAN. Voltammetric peak positions were affected by the nature of the electrolyte and its pH. Also, the effect of increasing film thickness was to observe increased peak heights for oxidation potential of HQ. The best results for the determination of HQ were obtained by DPV in Na2SO4 (pH 2.0) and PMT electrodes. Polymer coated electrodes were also used in an amperometric detector for flow injection analysis of HQ. The responses of the polymer electrode were 5–15 times larger as compared to those of bare platinum. PMT showed improved performance as an amperometric detector for flow injection analysis systems over other types of polymer electrodes. Detection limits as low as 1 × 10–9 M were achieved using the PMT, compared to 1 × 10–6 M using platinum electrodes.

Electrochemical Detection of Epinephrine at Organic Conducting Polymers Electrodes

In this paper, a rapid and sensitive modified electrode for the determination of Epinephrine (EP) is proposed. In this study, active compound EP was determined from commercial drug form based on electrochemical oxidation properties at various electrodes by voltammetric methods. Electrodes modified by the electrodeposition of conducting organic polymers such as poly(3-methylthiophene, PMT), polypyrrole (PPY) and polyaniline (PAN) were used as chemical sensors for voltammetric analysis and flow injection detection of EP. The electrochemical behavior of EP at conducting polymer electrodes was compared and the effects on behavior of electrolyte type and its pH and the film thickness were systematically examined. The results showed that the proposed modified surface catalyzes the oxidation of EP. Electrocatalytic efficiency decreases in order of PMT > PPY > PAN. Voltammetric peak positions were affected by the nature of the electrolyte and its pH. Also, the effect of increasing film thickness was to observe increased peak heights for oxidation potential of EP. The best results for the determination of EP were obtained by DPV in Na2SO4 (pH 2.0) and PMT electrodes. Polymer coated electrodes were also used in an amperometric detector for flow injection analysis of EP. The responses of the polymer electrode were 5–15 times larger as compared to those of bare platinum. PMT showed improved performance as an amperometric detector for flow injection analysis systems over other types of polymer electrodes. Detection limits as low as 1× 10–9 M were achieved using the PMT, compared to 1 × 10–6 M using platinum electrodes.

Determination of Iron in Environmental Water Samples by FIA-TLS

The determination of low concentration of iron in natural waters can be difficult due to the complexity of natural water, but primarily because it requires preconcentration of the sample with solvent extraction. In this work we report on results of thermal lens spectrometry (TLS) coupled to flow injection analysis (FIA) as a highly sensitive FIA-TLS method of iron detection. The concentration of iron redox species was determined using 1,10-phenanthroline (PHN), that forms stable complexes with Fe(II) ions which are characterized by an absorption maximum at 508 nm. The TLS system using a 633 nm probe laser and 530 nm pump laser beam was exploited for on-line detection in flow injection analysis, where a PHN solution was used as the carrier solution for FIA. The concentration of the complexing agent affects the quality of the TLS signal, and the optimal concentration was found at 1 mM PHN. The achieved limits of detection (LODs) for Fe(II) and total iron were 33 nM for Fe(II) and 21 nM for total iron concentration. The method was further validated by determining the linear concentration range, specificity in terms of analytical yield and by determining concentration of iron in a water sample from a local water stream.

Pyridoxal 5'-phosphate assay based on lucigenin chemiluminescence.

The authors describe the first chemiluminescence (CL) based method for determination of pyridoxal 5'-phosphate (PLP). PLP is found to generate intense CL with lucigenin higher than that of the conventional lucigenin-H2O2 system by a factor of about 9.0. This new finding is used to be in a detection method for PLP via flow injection analysis (FIA). Response is linear in the 50nM to 200μM PLP concentration range with a correlation coefficient of 0.998, and the detection limit (at an S/N of 3) is 6.9nM. The assay is highly selective over various amino acids, vitamins, sugars, coenzymes and metal ions cofactors. It exhibits advantages over the commonly employed HPLC methods in that it is rapid, more economic, eco-friendly and high throughput FIA detection of PLP without the need for toxic derivatization reagents, organic solvents, and HPLC instrumentation. The method was successfully applied to the determination of PLP in (spiked) human blood samples with recoveries in the range from 96.2-101.6% with % RSD < 4.0. The new system is also employed to determine lucigenin in the linear range of 0.3 to 100.0μM with a correlation coefficient of 0.994 and the limit of detection is 0.04μM. Graphical abstract Schematic of the chemiluminescent assay for pyridoxal 5'-phosphate (PLP). Lucigenin-PLP demonstrates 9-fold strongerchemiluminescence intensity than the lucigenin-H2O2 system. The detection limit of PLP is 6.9nM. The method can detect PLP in human serum with good recoveries.

Feedback-amplified electrochemical dual-plate boron-doped diamond microtrench detector for flow injection analysis.

An electrochemical flow cell with a boron‐doped diamond dual‐plate microtrench electrode has been developed and demonstrated for hydroquinone flow injection electroanalysis in phosphate buffer pH 7. Using the electrochemical generator‐collector feedback detector improves the sensitivity by one order of magnitude (when compared to a single working electrode detector). The diffusion process is switched from an analyte consuming “external” process to an analyte regenerating “internal” process with benefits in selectivity and sensitivity.

Fe&lt;sup&gt;3+&lt;/sup&gt; - Ion Selective Electrode Developed as a Detector in Flow Injection Analysis

Fe&lt;sup&gt;3+&lt;/sup&gt; - Ion Selective Electrode Developed as a Detector in Flow Injection Analysis

Design of a novel magnetic particles based electrochemical biosensor for organophosphate insecticide detection in flow injection analysis

The fabrication of transducer interfaces with improved electroanalytical performance is still a challenge in the field of advanced flow based electrochemical biosensors. The use of magnetic nanoparticles for such a purpose to replace the routinely used immobilization matrix including glass, membrane, polymer, gel beads, sol–gel supports, porous silicon matrix, and porous monolithic materials is well documented in the recent literature. However, the application of magneto-based methods is restricted due to lack of reproducibility and renewal of the sensor surface. To overcome these limitations, the present work described a novel configuration strategy to integrate magnetic nanobeads into the flow based system to achieve the reproducible and renewable sensing surface. The designed flow based sensor was demonstrated for the detection of organophosphate insecticides using acetylcholinesterase (AChE) enzyme. System parameters such as optimal bead injection and flow rate were studied prior to insecticides analysis. The system can be potentially applied for on-line assessment in a sensitive, automatic, inexpensive, continuous and simple way for any other analyte of interest.

Quercetin tethered pristine-multiwalled carbon nanotube modified glassy carbon electrode as an efficient electrochemical detector for flow injection analysis of hydrazine in cigarette tobacco samples

Hydrazine is one of the hazardous chemicals present in tobacco and known to be human carcinogen. It is highly challenging to detect hydrazine present in the tobacco selectively. Since, hydrazine molecule didn’t have any chromophore, indirect methods like separation coupled derivatization technique have been reported for the detection. Herein, we report a direct and separation-less flow injection analysis (FIA) coupled electrochemical detection technique (ECD) for hydrazine in tobacco. Quercetin (Qn, a plant-derived flavonoid found in fruits, vegetables, leaves and grains) tethered pristine-multiwalled carbon nanotube modified glassy carbon electrode (GCE/pristine-MWCNT@Qn) has been developed as a selective electrochemical detector for FIA and characterized by electro-chemical and physico-chemical techniques. At an optimal condition the new FIA-ECD showed a hydrazine calibration plot in a range 5–3000μM with a detection limit value 136nM/20μL. This electrochemical detector is found to be tolerable to several electro-active chemical entities such as ascorbic acid, uric acid, dopamine, cysteine, nitrite, benzene, ammonium chloride, nitrate, citric acid, oxalic acid (negligible interferences), aromatic amine and sulfide. The applicability of this technique is further tested by analyzing the hydrazine content in different brand of cigarettes with appreciable recovery values.

Polyion Selective Polymeric Membrane-Based Pulstrode as a Detector in Flow-Injection Analysis

A method for the detection of polyions using fully reversible polyion selective polymeric membrane type pulstrodes as detectors in a flow-injection analysis (FIA) system is examined. The detection electrode consists of a plasticized polymeric membrane doped with 10 wt % of tridodecylmethylammonium-dinonylnaphthalene sulfonate (TDMA/DNNS) ion-exchanger salt. The pulse sequence used involves a short (1 s) galvanostatic pulse, an open-circuit pulse (0.5 s) during which the EMF of the cell is measured, and a longer (15 s) potentiostatic pulse to return the membrane to its original chemical composition. It is shown that total pulse sequence times can be optimized to yield reproducible real-time detection of injected samples of protamine and heparin at up to 20 samples/h. Further, it is shown that the same membrane detector can be employed for FIA detection of both polycations at levels ≥10 μg/mL and polyanions at levels of ≥40 μg/mL by changing the direction of the galvanostatic pulse. The methodology described may also be applicable in the detection of polyionic species at low levels in other flowing configurations, such as in liquid chromatography and capillary electrophoresis.

Cucurbit[8]uril-based electrochemical sensors as detectors in flow injection analysis. Application to dopamine determination in serum samples

The results of the development of cucurbit[8]uril (CB[8]) electrochemical sensors and their performance as electrochemical transducers in a flow injection analysis (FIA) system are described. Two electrodes were designed, using either PVC or Nafion, to immobilise the macrocyclic receptor on a glassy carbon electrode (GCE) surface and used for dopamine (Dop) determination. 1H NMR and MS experiments were conducted to corroborate the formation of the CB[8]–Dop complex formation. Once all of the experimental variables were optimised, the developed methodologies achieved Dop detection limits of as low as 9.9×10−8M in the case of the Nafion-CB[8] based electrode and 2.6×10−8M for the case of the PVC-CB[8] electrode. For both sensors, the relative error values, Er (%), were lower than 13.9% and the relative standard deviation, RSD (%), ranged from 1.0% to 9.3% across the concentration range assayed, indicating that the methods proposed under flow conditions were of acceptable accuracy and precision. The electrodes were sufficiently durable to be used under flow conditions with no loss of reproducibility for approx. 85 successive analyses. Under optimised conditions, we were able to obtain sampling frequencies of 55 and 72samplesh−1 for the Nafion-CB[8] and PVC-CB[8]-modified electrodes, respectively. The elimination of any interference from ascorbic acid (Asc) in the Dop analysis demonstrates that the use of CB[8] leads to an additional selectivity in the method.

Oligonucleotide-functionalized silver nanoparticle extraction and laser-induced fluorescence for ultrasensitive detection of mercury(II) ion

This study describes the development of a simple, sensitive, and selective detection system for Hg2+ ion by combining nanoparticle extraction, fluorescent dye labeling, and flow injection analysis (FIA) detection. Repeats of 33 thymine nucleotides-functionalized silver nanoparticles (T33–AgNPs) specifically capture Hg2+ from aqueous solution through the coordination between T33 and Hg2+. Meanwhile, Hg2+ ion drives a T33 conformational change from a random coil to a folded structure. The T33–Hg2+complexes adsorbed on the NP surface were collected from the initial sample by centrifugation, and they were then detached from the NP surface by addition of H2O2. The T33–Hg2+ complexes preferentially bind to SYBR Green I (SG), enhancing the SG fluorescence. By contrast, SG fluoresces only weakly in the presence of T33 alone. The extraction efficiency of Hg2+ was highly dependent on polythymine length, the concentration of T33–AgNPs, and the incubaton time of T33–AgNPs with Hg2+. Under optimal extraction and labeling conditions, FIA detection showed the limit of detection (at a signal-to-noise ratio of three) for Hg2+of 3pM. The selectivity of our analytical system is more than 1000-fold for Hg2+ over any metal ions. We validated the applicability of this system for the determination of Hg2+ concentrations in tap water.

Electrochemical Detection of Sugar-related Compounds Using Boron-doped Diamond Electrodes

Electrochemical detection of sugar-related compounds was conducted using a boron-doped diamond (BDD) electrode as a detector for flow-injection analysis (FIA). Sugar-related compounds oxidize at high applied potentials, for which the BDD electrode is suitable for electrochemical measurements. Conditions for an FIA system with a BDD detector were optimized, and the following detection limits were achieved for sugar-related compounds: monosaccharides, 25-100 pmol; sugar alcohols, 10 pmol; and oligosaccharides, 10 pmol. The detection limit for monosaccharide D-glucose (Glu) was 105 pmol (S/N = 3). A linear range was acquired from the detection limit to 50 nmol, and the relative standard deviation was 0.65% (20 nmol, n = 6). A high-performance liquid chromatography (HPLC) column was added to the system between the sample injector and the detector and detection limits to the picomole level were achieved, which is the same for the HPLC system and the FIA system. The electrochemical oxidation reaction of Glu was examined using cyclic voltammetry with the BDD detector. The reaction proved to be irreversible, and proceeded according to the following two-step mechanism: (1) application of a high potential (2.00 V vs. Ag/AgCl) to the electrode causes water to electrolyze on the electrode surface with the simultaneous generation of a hydroxyl radical on the surface, and (2) the hydroxyl radical indirectly oxidizes Glu. Thus, Glu can be detected by an increase in the oxidation current caused by reactions with hydroxy radicals.

An electrochemical gas sensor based on paper supported room temperature ionic liquids

A sensitive and fast-responding membrane-free amperometric gas sensor is described, consisting of a small filter paper foil soaked with a room temperature ionic liquid (RTIL), upon which three electrodes are screen printed with carbon ink, using a suitable mask. It takes advantage of the high electrical conductivity and negligible vapour pressure of RTILs as well as their easy immobilization into a porous and inexpensive supporting material such as paper. Moreover, thanks to a careful control of the preparation procedure, a very close contact between the RTIL and electrode material can be achieved so as to allow gaseous analytes to undergo charge transfer just as soon as they reach the three-phase sites where the electrode material, paper supported RTIL and gas phase meet. Thus, the adverse effect on recorded currents of slow steps such as analyte diffusion and dissolution in a solvent is avoided. To evaluate the performance of this device, it was used as a wall-jet amperometric detector for flow injection analysis of 1-butanethiol vapours, adopted as the model gaseous analyte, present in headspace samples in equilibrium with aqueous solutions at controlled concentrations. With this purpose, the RTIL soaked paper electrochemical detector (RTIL-PED) was assembled by using 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide as the wicking RTIL and printing the working electrode with carbon ink doped with cobalt(II) phthalocyanine, to profit from its ability to electrocatalyze thiol oxidation. The results obtained were quite satisfactory (detection limit: 0.5 μM; dynamic range: 2-200 μM, both referring to solution concentrations; correlation coefficient: 0.998; repeatability: ±7% RSD; long-term stability: 9%), thus suggesting the possible use of this device for manifold applications.

Studies of the Electrochemical Degradation of Acetaminophen Using a Real‐Time Biomimetic Sensor

AbstractReal‐time monitoring of the electrochemical degradation of acetaminophen was performed using a biomimetic sensor coupled to a flow injection analysis (FIA) system. Degradation of the drug was carried out at constant current density (24 to 180 mA cm−2) in an electrolyte consisting of 0.1 mol L−1 K2SO4/5.0×10−4 mol L−1 FeSO4⋅7H2O. Two commercial DSA anodes (DSA‐Cl2 and DSA‐O2) were compared. The degradation process was monitored on‐line using an amperometric sensor based on the biomimetic catalyst iron(III) tetrapyridinoporphyrazine (FeTPyPz), coupled to the degradation cell. The optimized FIA detection system employed the electrolyte solution as carrier, a flow rate of 1.25 mL min−1 and an injected sample volume of 75 µL. The real‐time data obtained showed, as expected, that acetaminophen degradation followed pseudo‐first order kinetics, with the DSA‐Cl2 anode showing a higher efficiency according to the calculated apparent rate constant values. The advantage of the proposed on‐line system is that a larger number of points can be monitored in a shorter time compared to other off‐line methods, which improves the accuracy of estimates of electrochemical degradation constants.

Microfabricated Electrochemical Detector for High-Performance Liquid Chromatography

A microfabricated electrochemical cell has been developed as a disposable detector for flow injection analysis (FIA) and high-performance liquid chromatography (HPLC). The simplicity of the fabrication process allows this detector to be used as a low-cost, disposable device that can be replaced easily if its performance degrades rather than disassembling the detector and polishing the electrode surface, which is the usual procedure. The detector consists of thin film-metal electrodes-platinum working electrode, platinum auxiliary electrode, and silver/silver chloride coated on Pt reference electrode-deposited on a polyimide substrate with a locking layer of chromium in between. A microfluidic cover made of polyimide directs the solution flow across the electrodes. The detector was evaluated with FIA of ferrocyanide and HPLC of ascorbic acid and acetaminophen and a mixture of two pharmaceutical compounds-dextrorphan and levallorphan-with acetaminophen internal standard. The HPLC calibration curves showed good linearity (R(2) > 0.99). Limits of detection were 1 nM for acetaminophen, 1 nM for ascorbic acid, 50 nM for dextrorphan, and 80 nM for levallorphan. When detected with a commercial detector dextrorphan and levallorphan had lower limits of detection, 3 and 5 nM, respectively. Chromatograms of the mixture were comparable to those obtained with a commercial detector. The detector could be used continuously for about 48 h with FIA and about 10-20 h with HPLC after which performance gradually degraded as the AgCl on the reference electrode dissolved causing loss of potential control.

Characterization of BSA unfolding and aggregation using a single-capillary viscometer and dynamic surface tension detector

A dynamic surface tension detector (DSTD) has been equipped with an additional pressure sensor for simultaneous viscosity measurements, as a detector for flow injection analysis. The viscosity measurement is based on a single capillary viscometer (SCV) placed in parallel configuration with the DSTD. The viscometer in the optimized conditions consists of a PEEK capillary (i.d.=0.25mm, L=75cm) kept at constant temperature using a thermostatic bath, which leads on the two sides to the two arms of a differential piezoelectric pressure transducer with a range of 0–35psi. The DSTD, described previously, measures the changing pressure across the liquid/air interface of 2μL drops repeatedly forming at the end of a capillary.SCV performance has been evaluated by measuring dynamic viscosity of water/glycerol mixtures analysed in flow injection and comparing the results with the values reported in the literature. The detection limits of SCV and DSTD, calculated as 3σ of the blank, were 0.012cP and 0.6dyncm−1, respectively.The FI-SCV-DSTD system has been applied to the study of temperature-induced denaturation/aggregation process in bovine serum albumin (BSA).The results have been supported and discussed with respect to BSA conformational analysis performed using Fourier Transform infrared spectroscopy.