Electrochemical Determination of Bisphenol A at Multi-walled Carbon Nanotubes/Poly (Crystal Violet) Modified Glassy Carbon Electrode

Bisphenol A (BPA) can disrupt endocrine system. In this study, a novel and sensitive electrochemical senor based on multi-walled carbon nanotubes (MWCNTs) and poly crystal violet (PCV) modified glass carbon electrode (GCE) was developed for determination of BPA. The morphologies and properties of modified electrode were characterized by scanning electron microscopy and electrochemical impedance spectra. Compared with bare GCE and other modified electrodes, this MWCNTs/PCV/GCE exhibited an excellent electrocatalytic role for the oxidation of BPA by significantly enhancing the current response and decreasing the BPA oxidation overpotential. Under optimum conditions, the electrochemical sensor can be applied to the quantification of BPA by linear sweep voltammetry (LSV) with a linear range covering 5 × 10^?8–1 × 10^?4 mol L^?1 (with a correlation coefficient of 0.9969), and the limit detection was 1 × 10^?8 mol L^?1 (S/N = 3). The recovery was between 98.38 and 103.51% in real plastic samples. This strategy might enable more opportunities for the electrochemical determination of BPA in practical applications.     

Study on the Electrochemical Properties of Kojic Acid at a Poly(glutamic Acid)-Modified Glassy Carbon Electrode and Its Analytical Application

A poly(glutamic acid)-modified glassy carbon electrode (PGA/GCE) for the electrochemical determination of kojic acid was developed. The polymerization mechanism of glutamic acid at the glassy carbon electrode, the electrocatalytic mechanism of the poly(glutamic acid) film toward kojic acid, and the electrochemical behavior of kojic acid at the PGA/GCE were investigated. The studies revealed that the oxidation of kojic acid at the PGA/GCE is greatly facilitated, which is attributed to the weakening of the bond energy between oxygen and hydrogen due to the formation of hydrogen bond between hydroxyl group in kojic acid and the nitrogen atom in poly(glutamic acid). The oxidation of kojic acid at the PGA/GCE is a one proton–one electron process. The catalytic effect was further used to determine kojic acid by cyclic voltammetry. The oxidation peak current shows a linear relationship with the concentrations of kojic acid in the range of 8.00?×?10^?6 to 6.60?×?10^?4 mol L^?1 with the detection limit of 8.00?×?10^?7 mol L^?1. The modified electrode shows excellent sensitivity, selectivity, and stability and has been applied to detect kojic acid in a variety of food products with satisfactory results.     

SWCNT-modified carbon paste electrode as an electrochemical sensor for histamine determination in alcoholic beverages

In this work, a simple and rapid electrochemical method is presented for the voltammetric determination of histamine based on carbon paste electrodes bulk-modified with single-walled carbon nanotubes. As monitored in cyclic voltammetry histamine undergoes an irreversible electrochemical oxidation with a peak potential of ca. +1.25 V (vs. Ag/AgCl, 3 mol L^?1 KCl) in phosphate buffer solution (PBS, 0.1 mol L^?1, pH 6.0). At optimized differential pulse voltammetric parameters, the current response of histamine was linearly proportional to its concentration in the range from 4.5 to 720 μmol L^?1. A low limit of detection of 1.26 μmol L^?1 and a limit of quantification of 3.78 μmol L^?1 of histamine, as well as good reproducibility (RSD?=?0.48–3.40 %) were obtained using the carbon paste electrode modified with single-walled carbon nanotubes. The proposed sensor was successfully applied to the determination of histamine in commercial beer and wine samples.     

Determination of Rutin in Black Tea by Adsorption Voltammetry (AdV) in the Presence of Morin and Quercetin

This paper presents a sensitive method to rutin determination on a screen-printed multi-walled carbon nanotube electrode modified with poly(3,4-ethylenedioxythiophene) and ionic liquid (SMWCNT-PEDOT-IL). Several studies show that rutin may be absorbed onto the surface of electrodes modified with PEDOT. On the other hand, the presence of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) on the surface of the modified electrode increased the oxidation current by nearly 30 % and facilitates the oxidation of rutin to values less positive potential compared with the modified electrode only with PEDOT. Cyclic voltammetry was used to quantify and characterize the modified electrode. pH and electrochemical parameters, potential adsorption, time adsorption, and scan rate were optimized based on the oxidation of rutin to obtain the following values: pH 6.0; Eads, ?0.10 V; tads, 80 s; and scan rate 50 mV s^?1. The detection limit (3σ) was 7.7?×?10^?8 mol L^?1 and the RSD was 1.5 %. The new method was used to quantify rutin in black tea samples in the presence of others flavones with consistent results.     

Sensitive and Selective Determination of Riboflavin in Milk and Soymilk Powder by Multi-walled Carbon Nanotubes and Ionic Liquid [BMPi]PF<Subscript>6</Subscript> Modified Electrode

A novel electrochemical method to detect riboflavin was proposed using a multi-walled carbon nanotubes and ionic liquid N-butyl-N-methyl-piperidinium hexafluorophosphate composite film modified glassy carbon electrode (MWNTs-[BMPi]PF₆/GCE). A well-defined CV behavior with a pair of sensitive and well-shaped redox peak was observed, and the response value of riboflavin at MWNTs-[BMPi]PF₆/GCE is much higher than that at MWNTs/GCE in 0.1 mol L^?1 HAc-NaAc buffer solution (pH 4.5). The electrochemical approach based on a sensitive DPV analytical signal exhibits an excellent analytical performance with a wide linear range (2.6 × 10^?8 to 1.3 × 10^?6 mol L^?1) and low detection limit (4.7 × 10^?9 mol L^?1) for the riboflavin. Moreover, the proposed method possesses a potential practical application value and can be employed for the quantitative analysis of trace riboflavin with a recovery of 95.8–102.4 % in food samples such as milk and soymilk powder.     

Electrochemical Determination of Tert-Butyl Hydroquinone in Edible Oil Samples at Poly (Crystal Violet) Modified Glassy Carbon Electrode

The synthetic phenolic antioxidant tert-butyl hydroquinone (TBHQ) is frequently associated to adverse health effects. A polymerized film of crystal violet (CV) was prepared on the surface of a glass carbon electrode (GCE) by electropolymerization in alkaline solution, and then the modified electrode was successfully used to determine TBHQ. This electrode was characterized by scanning electron microscopy and electrochemical impedance spectra. The voltammetric behavior of TBHQ over an extended pH range using cyclic voltammetry at poly (crystal violet) modified glassy carbon electrode (PCV/GCE) was also studied. The resulting electrode exhibited excellent electrocatalytic activity towards the oxidation of TBHQ, and this was confirmed by the observed increased redox peak currents and shifted potentials. The electrochemical sensor can be applied to the quantification of TBHQ with a linear range covering 5?×?10^?7–1?×?10^?4 mol?·?L^?1 (with a correlation coefficient of 0.9969) and the limit detection was 3?×?10^?8 mol?·?L^?1(S/N?=?3). The recovery was between 97.1 and 102 % in edible oil samples. The electrochemical sensor method was also compared with a HPLC method, which proves its capability in commercial market surveillance.     

Electrochemical determination of Sudan I in food products using a carbon nanotube-ionic liquid composite modified electrode

A sensitive and convenient electrochemical method was developed for the determination of Sudan I using a carbon nanotube-ionic liquid composite modified electrode with the enhancement effect of cetyltrimethyl ammonium bromide (CTAB). The modified electrode exhibited an obvious electrocatalytic activity towards the oxidation of Sudan I, and the oxidation peak current significantly increased in the presence of CTAB. The experimental parameters, such as solution pH, concentration of CTAB and accumulation time, were optimised for Sudan I determination. The oxidation peak current showed a linear relationship with the concentration of Sudan I in the range of 3.0 × 10^?8 to 3.1 × 10^?6 mol l^?1, with a detection limit of 8.0 × 10^?9 mol l^?1. The proposed method was successfully applied for the determination of Sudan I in food products of ketchup and chilli sauce.     

Electrochemical detection of pyrosine with electrochemically reduced graphene oxide modified glassy carbon electrode

Pyrosine detection and quantification was reported by voltammetry with the electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode (GCE). The differential pulse voltammograms of pyrosine on the modified GCE showed that pyrosine can be sensitively detected, which may be attributed to the large surface area of ERGO and the improved electron transfer ability of ERGO compared to graphene oxide. The effect of supporting electrolyte and its concentration on the detection of pyrosine was also investigated in this paper. The ERGO modified GCE showed a linear concentration range between 1.6 and 374 μmol L^?1 of pyrosine with a correlation coefficient of 0.9972, and the detection limit was as low as 1.2 × 10^?8 mol L^?1 (signal-to-noise ratio of 3).     

Sensitive Determination of Toxic Clenbuterol in Pig Meat and Pig Liver Based on a Carbon Nanopolymer Composite

The acidified single-walled carbon nanotubes (SWCNTs) were self-assembled on graphene oxide (GO) and then ultrasonically dispersed in a copolymer, Nafion solution, to form a GO/SWCNTs-Nafion polymer nanocomposite, which was employed to modify glassy carbon electrode (GCE). The surface morphological characteristics of different modified electrodes including bare GCE, GO-Nafion/GCE, and GO/SWCNTs-Nafion/GCE were imaged by scanning electron microscopy. For comparison, the differential pulse voltammetry and cyclic voltammetry behaviors were investigated, showing that the GO/SWCNTs-Nafion polymer composite has strong enhancement effect towards oxidation of clenbuterol (CLB). And the corresponding mechanism has been well discussed. During the reaction process, the anilino group of CLB molecule (1) was firstly oxidized to form a radical cation (2), exhibiting a characteristic oxidation peak (I) at 0.95 V, then two radical cations reacting via head-to-head coupling to form a diphenylamine intermediate (3), which was transformed into a CLB dimmer (4) through an azo bond by intramolecular electrons transferring under low potential, exhibiting a pair of reversible oxidation peak (II) and reduction peak (III). Under the optimum conditions, the composite modified electrode showed linear response to CLB in a concentration range of 1.0 × 10^?8~6.0 × 10^?6 mol/L with a detection limit of 6.0 × 10^?9 mol/L. The modified electrode possessed good selectivity, reproducibility, and stability. In comparison with two routine analytical methods like ELISA kit and high-performance liquid chromatography (HPLC), the electrode can be successfully applied to determination of content of CLB in pig meat and pig liver samples with a recovery rate of 96.4~104.2%, suggesting a promising application in food security field.     

Sensitive and Simple Voltammetric Detection of Sudan I by Using Platinum Nanoparticle-Modified Glassy Carbon Electrode in Food Samples

A highly sensitive and simple voltammetric method is developed for determination of Sudan I by using platinum nanoparticles modified the glassy carbon electrode. With the optimized experimental conditions, the anodic peak currents of Sudan I are proportional to its concentration in the range of 0.002–0.3 μmol L^?1 and 0.3–7.0 μmol L^?1, and the limit of detection of 0.7 nmol L^?1 is obtained. Some dynamic parameters are also investigated in this research. This proposed method is successfully applied to the detection of Sudan I in food, such as ketchup, chili powder, duck egg yolk, and chafing dish foodstuffs, which indicates its applicability and reliability.     

Carbon Nanotube–Ionic Liquid (CNT–IL) Nanocamposite Modified Sol-Gel Derived Carbon-Ceramic Electrode for Simultaneous Determination of Sunset Yellow and Tartrazine in Food Samples

Carbon-ceramic electrode modified with multi-walled carbon nanotubes–ionic liquid (MWCNTs–IL) nanocomposite was constructed. This electrode was used for electrochemical determination of food dyes Sunset Yellow (SY) and tartrazine (Tz). The modified electrode based on high surface area and high ionic conductivity of nanocomposite exhibited electrocatalytic effect for oxidation of SY and Tz; also, oxidation peak potentials of SY and Tz effectively separated on modified electrode, and their simultaneous determination was possible. Operational parameters, such as the amount of MWCNTs in suspension, IL volume, solution pH, and scan rate, which affect the analytical performance of determination, were optimized. The present electrode behaved linearly to Sunset Yellow and tartrazine in the concentration range of 4?×?10^?7 to 1.1?×?10^?4?M and 3?×?10^?6 to 0.7?×?10^?4?M with a detection limit of 10^?7?M (0.045 mg?L^?1) and 1.1?×?10^?6?M (0.59 mg?L^?1), respectively. The proposed method was successfully utilized for simultaneous determination of SY and Tz in different food samples, and the obtained results were in good agreement to those obtained by HPLC method.     

Simple Voltammetric Determination of Rhodamine B by Using the Glassy Carbon Electrode in Fruit Juice and Preserved Fruit

This paper reported an innovative simple voltammetric approach for determination of rhodamine B based on a glassy carbon electrode. Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behavior of rhodamine B. After optimizing the experimental conditions, the anodic peak current of rhodamine B was linear to its concentration in the range of 4.78–956.1 μg?L^?1, and the limit of detection was 2.93 μg?L^?1 in pH 4.0 buffer solution. The electrode showed good repeatability and acceptable selectivity. This method was successfully applied to the detection of rhodamine B in preserved fruit and fruit juice samples, which has shown good reliability.     

Electrochemical Determination of Phoxim in Food Samples Employing a Graphene-Modified Glassy Carbon Electrode

Employing a graphene-modified glassy carbon electrode, a sensitive and convenient electrochemical method for the determination of phoxim by linear sweep voltammetry was developed. The electrochemical behavior of phoxim at the modified electrode was studied by cyclic voltammetry. In citric acid–phosphate buffers, the modified electrode exhibited excellent electrocatalytical effect on the reduction of phoxim and this was further used for the determination of phoxim. Under optimized analytical conditions, the reduction peak current showed a linear relationship with the concentration of phoxim in a range of 5.97 to 5,966 μg L^?1, with a correlation coefficient of 0.9993 and a detection limit of 2.39 μg L^?1. The proposed method shows excellent sensitivity, selectivity, and linearity and has been successfully applied for the determination of phoxim in a variety of food samples with satisfactory results.     

Glucose Biosensor Based on a Glassy Carbon Electrode Modified with Multi-Walled Carbon Nanotubes-Chitosan for the Determination of Beef Freshness

In this study, the glucose biosensor was developed for the determination of the beef meat freshness based on a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and chitosan (Chi). Glucose oxidase (GOx) was immobilized onto the MWCNTs-Chi/GCE surface by cross-linking the enzyme through glutaraldehyde with bovine serum albumin (BSA). Glutaraldehyde solution (0.25%, w/w) was also added to prevent enzyme release. The properties of the developed biosensor were characterized with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) using [Fe (CN)₆]^3?/4?as the supporting electrolyte. The influence of various parameters was investigated, and 0.1 mol L^?1 PBS with pH = 6.4 was chosen as the optimal supporting electrolyte for this experiment. The linear relationship between the current and the concentration of glucose was obtained from 0.2 to 1.2 mmol L^?1, with a detection limit of 0.05 mM at a signal-to-noise ratio of 3 and displayed good linearity (R ² = 0.9902), while the biosensor showed a rapid response to glucose. In addition, the developed glucose biosensor was applied in the determination of glucose in beef as an indicator of beef freshness compared to the total volatile basic nitrogen (TVB-N) method. The glucose level was decreased with increasing beef storage time.     

Carbonaceous Materials-12: a Novel Highly Sensitive Graphene Oxide-Based Carbon Electrode: Preparation,Characterization, and Heavy Metal Analysis in Food Samples

Graphene oxide (GO) was covalently attached to glassy carbon (GC) electrode (GC–O–GO) for fabricating nanosensors to determine trace Pb²⁺ and Cd²⁺ using differential pulse anodic stripping voltammetry (DPASV). Surface characterization of the nanofilm-covered electrode was performed via electrochemical cyclic voltammetry (CV), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) techniques. Surface pKa of the GO covalent attached GC (GC–O–GO) was calculated via CV. Under optimal conditions, a linear response was found for Pb²⁺ and Cd²⁺ in the range from 1?×?10^?8 to 1?×?10^?12 M. The limit of detections (LODs) of Pb²⁺ and Cd²⁺ were 0.25 pM and 0.28 pM, respectively. The method shows good reproducibility, and stability was successfully applied to measure Pb²⁺ and Cd²⁺ levels in rice, soya, milk, and tap water samples, with good agreement with those obtained by the standard inductively coupled plasma optical emission spectrometry (ICP-OES) method. The method was evaluated by application with the simultaneous determination of the ions in food samples (n?=?6) using the standard addition method. The recoveries of the Pb²⁺ and Cd²⁺ were up to 98 %.     

Development of an Electrochemical Sensor for the Determination of Amaranth: a Synthetic Dye in Soft Drinks

The voltammetric behaviour of synthetic food colourant, amaranth, was studied using a multiwalled carbon nanotube (MWCNT) thin film-modified gold electrode in 0.1 M acetate buffer solution of pH 5.0. A well-defined oxidation peak was obtained for amaranth at 0.792 V with the modified electrode. The diffusion controlled oxidation of amaranth at the modified electrode can be attributed to the electrocatalytic nature of MWCNT, since the bare electrode has not produced an electrochemical signal under the same experimental conditions. The operational parameters such as supporting electrolyte, pH of the solution and amount of MWCNT–Nafion suspension were optimised. Under optimum conditions, the oxidation peak current varies linearly with concentration in the range from 1.0?×?10^?5 M to 1.0?×?10^?6 M with a limit of detection at 6.8?×?10^?8 M. The developed sensor has good sensitivity and selectivity towards oxidation of amaranth. The sensor was successfully employed for the determination of amaranth in three different samples of soft drinks, and the results were in good agreement with the standard spectrophotometric method.     

Determination of Glucose in Food by the Ionic Liquid and Carbon Nanotubes Modified Dual-Enzymatic Sensors

A sensitive electrochemical glucose biosensor based on chitosan (CS)/glucose oxidase (GOx)/catalase (CAT)/CS?+?carboxylic multi-walled carbon nanotubes (MWCNTs-COOH)?+?ionic liquid (IL) film modified glassy carbon electrode has been developed and its characteristics were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Hydrogen peroxide (H₂O₂) generated during the enzymatic reaction of GOx with glucose could be decomposed by catalase, resulting in the higher sensitivity. The linear range and detection limit were found to be 0.5–100 and 0.2 μmol L^?1, respectively. The proposed biosensor was successfully applied for the determination of glucose in drink and food samples with the spiked recoveries in the range of 95.5 to 101.5 %.     

Application of Molecularly Imprinted Polymer Appended onto CdSe/ZnS Quantum Dots for Optosensing of Tocopherol in Rice

Acting as a fluorescence sensing material, the molecularly imprinted polymer (MIP) appended onto quantum dots (QDs) was constructed through anchoring the MIP layer on CdSe/ZnS QDs by simple embedding for highly selective and sensitive optosensing of tocopherol (TP) in rice. The resulting composite of QDs with MIP showed higher template selectivity versus that of non-imprinted polymer (NIP). Under optimal conditions, the relative fluorescence intensity of MIP appended onto QDs decreased linearly (r ²?>?0.99) with the increasing TP in the concentration in the range of 1.16?×?10^?7–1.74?×?10^?3 mol L^?1 with a detection limit of 5.80?×?10^?8 mol L^?1, and the precision for five replicate detections of 1.0?×?10^?4 mol L^?1 TP was 2.17 % (relative standard deviation). Recoveries of 90.40 to 100.20 % were achieved by direct detection when MIP appended onto QDs was used for the selective separation of TP in rice samples.     

Application of ZnO/CNTs Nanocomposite Ionic Liquid Paste Electrode as a Sensitive Voltammetric Sensor for Determination of Ascorbic Acid in Food Samples

In this study, a simple and rapid analytical method development for ascorbic acid (AA) determination in food samples by using differential pulse voltammetry (DPV) method on ZnO/CNTs nanocomposite ionic liquid modified carbon paste electrode. For this, several parameters, such as ZnO/CNTs nanocomposite, ionic liquid ratio, and pH, have been studied. The cyclic voltammogram showed an irreversible oxidation peak at 0.61 V (vs. Ag/AgCl_sat), which corresponded to the oxidation of AA. Compared to common carbon paste electrode, the electrochemical response was greatly improved. Under the optimized conditions, the oxidation peak current of AA showed linear dynamic range 0.1–450 μmol l^?1 with a detection limit of 0.07 μmol l^?1, using the DPV method. The proposed sensor was successfully applied to the determination of AA in fresh vegetable juice, fruit juices and food supplement samples without previous preparation and was compared with a published electrochemical method.     

Electrochemical Behaviors of 2-Amino-3-Hydroxypyridine onto the Glassy Carbon Sensor Electrode: Simultaneous and Independent Determinations of Quercetin, Galangin, 3-Hydroxyflavone, and Chrysin

Flavonoids, with high antioxidant activity in fruits and vegetables, are natural vegetable dyes synthesized from phenylalanine. They are very essential for human health due to their activity as free radical acceptors. In this paper, the availability in the determination of quercetin (Que), galangin (Gal), 3-hydroxyflavone (3HF), and chrysin (Chr) of a modified glassy carbon (GC) sensor electrode using 2-amino-3-hydroxypyridine (AHP) was examined separately and simultaneously by cyclic voltammetry (CV). Surface characterization of modified electrodes was performed using CV, electrochemical impedance spectroscopy, and scanning electron microscopy techniques. The modification of AHP onto the GC electrode surface was carried out between ?150 and +600 mV potential range using 100 mV?s^?1 scanning rate with 30 cycles. The binding of flavonoid derivatives onto the modified surface was performed between +300 and +1,700 mV potential range using 100 mV?s^?1 scanning rate with 10 cycles. The usability of the modified electrode was examined in the determination of some flavonoids by square wave voltammetry. From the experimental results, it was found out that Que, 3HF, and Chr; Gal, 3HF, and Chr; and 3HF and Chr can be determined simultaneously by using an AHP-modified GC sensor electrode. Also, these molecules can easily be determined separately by using the modified electrode.