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.     

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.     

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.     

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.     

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 %.     

High Sensitive Method for Determination of the Toxic Bisphenol A in Food/Beverage Packaging and Thermal Paper Using Glassy Carbon Electrode Modified with Carbon Black Nanoparticles

A voltammetric method for fast and high sensitive determination of Bisphenol A (BPA) using glassy carbon electrode (GC) modified with carbon black nanoparticles (CB) was developed. Cyclic voltammetry study in the 0.1 M phosphates of pH = 7.0 gave single anodic peak at 578 mV. Adsorption-controlled oxidation of BPA was found to be irreversible with the participation of two electrons and two protons. The proposed CB/GC electrode significantly improved the oxidation peak current of BPA compared to the bare electrode. Under the optimum conditions, calibration curve was linear in the concentration of BPA from 0.01 to 3 × 10^?6 mol L^?1 with the detection limit of 3.4 × 10^?9 mol L^?1. Moreover, the proposed method was successfully validated by studying the recovery of BPA in commonly available samples: thermal paper (receipt, ticket) and food/beverages packaging. This paper introduces carbon black as a new, perspective material for electrode modification used in voltammetry.     

Novel Sensor Fabrication for the Determination of Nanomolar Concentrations of Hg2+ in Some Foods and Water Samples Based on Multi-walled Carbon Nanotubes/Ionic Liquid and a New Schiff Base

The air and water stable room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [BMP]Tf₂N, multi-walled carbon nanotubes (MWCNTs), graphite powder and also a new synthesized Schiff base have been used to fabricate a new carbon composite electrode with very attractive sensing behavior. The new Schiff base was synthesized to apply as a selective agent in electrochemical responses of the voltammetric sensor for the determination of mercury (II) ions in aqueous solutions. The proposed sensor allowed the determination of mercury (II) in the wide linear dynamic range of 0.2–260.0 nmol l^?1. The limit of detection (LOD) was noticed to be 0.05 nmol l^?1. The prepared electrode was used for mercury (II) determination in the real 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 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.     

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.     

Simultaneous pre-concentration of Pb and Sn in food samples and determination by atomic absorption spectrometry

A cloud point extraction (CPE) method has been developed for the pre-concentration and simultaneous determination of lead [Pb(II)] and tin [Sn(II)] using Acridine Orange as complexing reagent and mediated by nonionic surfactant (Triton X-114) by flame atomic absorption spectrometry (FAAS). The main factors affecting analytical performance of CPE have been investigated in detail. The extracted surfactant-rich phase was diluted with (1.0 mol L^?1) nitric acid in methanol, prior to subjecting FAAS. The calibration graphs obtained from Pb(II) and Sn(II) were linear in the concentration ranges of 5–1,000 and 10–5,000 μg L^?1 with detection limits of 1.40 and 2.86 μg L^?1, respectively. The relative standard deviations for 10 replicates containing 25 μg L^?1 of Pb(II) and Sn(II) were 2.15 and 2.50 %, respectively. The analytical procedure was verified by the analysis of the standard reference materials NWTMDA-61.2 (water-trace elements) and NIST SRM 1548a (typical diet). The developed method has been applied to the simultaneous determination of total Pb and Sn in canned food samples including juices, tomato paste, corn, and green pea.     

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).     

A non-diazotization-coupling reaction-based colorimetric determination of nitrite in tap water and milk

A non-diazotization-coupling reaction-based colorimetric method was developed and validated for the determination of nitrite in tap water and milk samples. Under acidic condition, nitrite could selectively react with pyrrole, resulting in the emerging of a new absorption peak at 509 nm and a distinct color change from clear to red, with which the concentration of nitrite can be determined indirectly. Excellent linear range was achieved from 0.72 to 40.0 μmol L^?1 with a detection limit of 0.22 μmol L^?1. The detection limit was lower than or comparable to most of the recently published methods. The experimental conditions were optimized, and effects of coexisting substances were evaluated, and the results showed excellent priority since a certain amount of other anions, including SO₃ ^?, SeO₃ ^? and other acid radicals, would not interfere with the measurement. We highlighted the simplicity and efficiency of this method as no diazotization-coupling procedure and toxic aniline were involved. Determination of nitrite in tap water and milk samples was performed.     

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.     

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.     

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.     

Characterization of Chlorogenic Acids in Coffee by Flow-Through Chronopotentiometry

In this study, flow-through chronopotentiometry (FTCP) has been developed as an electroanalytical method for characterization (identification and quantification) of chlorogenic acids (CGAs) in coffees. The characterization of CGAs in coffee was based on the electrochemical behavior of the main chlorogenic acid (CGAs) isomers presented in coffee (caffeoylquinic acids (CQAs), dicaffeoylquinic acids (diCQAs), and feruloylquinic acids (FQAs)) and the spiking of CGAs standards in coffee samples. The FTCP study has shown that electrochemical properties of CGAs strongly depend on their chemical structure and electronic properties, particularly on the presence of electron-donating ?OH, ?CH═CH? and ?OCH₃ groups and strong electron-withdrawing ester (?COOR) group presented in their structure. The FTCP measurements of coffee samples show that their electrochemical behavior is very similar to that of CGAs. Therefore, FTCP can be used for characterization of CGAs and determination of their content in coffees. 5-O-Caffeoylquinic acid (5-CQA), prevailed CGAs in coffees, was used as a standard for quantification of total CGA content in coffee. The linear calibration curve of 5-CQA was observed within the concentration range of 5 to 100 μmol L^?1 with the limit of detection 5.7·10^?7 mol L^?1. The total CGA content of coffees has been expressed in 5-CGA equivalents per 100 g of coffee. It was shown that FTCP is a very sensitive, precise, and acurate method for determination of total CGA content in coffee. It should be noted that in presented investigation, FTCP was for the first time used for the study of electrochemical properties of polyphenolic antioxidants (including CGAs) and their characterization in some of the food samples.     

Amperometric Determination of Quercetin in Some Foods by Magnetic Core/Shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@ZnO Nanoparticles Modified Glassy Carbon Electrode

In this paper, Fe₃O₄@ZnO core/shell magnetic nanoparticles (MNPs) have been synthesized by a simple method, to modify carbon paste/glassy carbon electrode and improve its efficiency for determination of quercetin. The synthesized MNPs were characterized by X-ray powder diffraction (XRD), transmission electronic microscope (TEM), and scanning electronic microscope (SEM). SEM and TEM results show that the prepared Fe₃O₄@ZnO MNPs are made of the spherical shape particles with an average size of about 15 nm. The electrochemical behavior of quercetin at the surface of modified electrode was investigated. Under the optimal conditions, a linearity range of quercetin was 7.9?×?10^?7 to 6.1?×?10^?5 mol/L (0.24–18.44 mg/L) with detection limit (S/N?=?3) and sensitivity of 0.16 μmol/L (0.048 mg/L) and 0.04 μA/μM, respectively. The validated method was applied successfully for determination of quercetin in some foods and human breast milk.     

Amperometric Photosensor Based on Acridine Orange/TiO<Subscript>2</Subscript> for Chlorogenic Acid Determination in Food Samples

The authors describe a novel sensor for chlorogenic acid (CGA) detection/quantification in food samples. The photosensor is based on a composite of titanium dioxide (TiO₂) and acridine orange (AO). The synergism between AO and TiO₂ was revealed under visible LED light irradiation by high photocurrents for CGA, when compared to each component of the composite material. A detection limit of 0.54 μmol L^?1 and a linear response range from 2 to 200 μmol L^?1 for CGA detection were achieved. The selectivity of the sensor was tested by using common interferents on samples containing chlorogenic acid and results suggested that there is no significant interference in the analyte response, indicating a good selectivity. Finally, the photosensor was successfully applied in the determination of CGA in samples of coffee, tea, and apple juice, with recoveries ranging from 100.9 to 102.4%, suggesting a good accuracy for the proposed method.     

Ultra-Trace Determination of Co (ІІ) in Real Samples Using Ion Pair-Based Dispersive Liquid-Liquid Microextraction Followed by Electrothermal Atomic Absorption Spectrometry

Ion pair-based dispersive liquid-liquid microextraction technique was used for preconcentration and determination of ultra-trace levels of Co (??) followed by electrothermal atomic absorption spectrometry (ETAAS). Thiocyanate (SCN^?) forms an anionic complex with Co (??) followed by addition of cetylpyridinium chloride (CPC) as a positive counterion to produce hydrophobic cobalt-thiocyanate-CPC complex. The resulting hydrophobic complex was extracted into the fine droplets of carbon tetrachloride by dispersive liquid-liquid microextraction (DLLME). In DLLME, a mixture of 1.5 mL of acetone (as disperser solvent) containing 40 μL of carbon tetrachloride (as extraction solvent) was rapidly injected into the sample solution to extract the hydrophobic cobalt-thiocyanate-CPC complex. Under the optimum conditions, the calibration curve was linear in the range of 0.08–1.5 μg L^?1 of Co (??) with a correlation coefficient of 0.9997. The relative standard deviation (RSD, %) based on six replicate analyses of 0.5 μg L^?1 of Co (??) was 3.7 %, and the limit of detection (LOD) was 0.02 μg L^?1. The accuracy of the proposed method was evaluated by the analysis of a certified reference material and spike method. The proposed method was successfully applied for determination of ultra-trace levels of Co (??) in different water samples and spinach leaves.