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.     

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.     

A novel nanosensor based on Pt:Co nanoalloy ionic liquid carbon paste electrode for voltammetric determination of vitamin B9 in food samples

In this work we describe a novel nanoalloy (Pt:Co) room temperature ionic liquid (RTIL) modified carbon paste electrode as a high sensitive sensor for voltammetric determination of vitamin B₉ in food samples. The sensor exhibits an enhanced effectiveness for the electro-oxidation of vitamin B₉ in aqueous solution. The oxidation peak potential for this matter at a surface of the ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) Pt:Co carbon paste electrode (Pt:Co/IL/CPE) appeared at 685 mV that was about 110 mV lower than the oxidation peak potential at the surface of the traditional carbon paste electrode (CPE) under similar condition. The mechanism of the electro-oxidation process on the surface of the modified electrode was analyzed. Square wave voltammetry (SWV) was applied as a very sensitive electrochemical method for the determination of sub-micro-molar amounts of vitamin B₉. The linear response range and detection limit were found to be 1.0 × 10⁻⁷ to 5.0 × 10⁻⁴ M and 4.0 × 10⁻⁸ M, respectively. The prepared modified electrode shows several advantages such as simple preparation method, high stability, high sensitivity, and excellent catalytic activity, long-term stability and remarkable voltammetric reproducibility for eletrooxidation of vitamin B₉. The proposed sensor was successfully applied for the determination of vitamin B₉ in food samples.     

An Electrochemical Nanosensor for Simultaneous Voltammetric Determination of Ascorbic Acid and Sudan I in Food Samples

In this work, we describe application of a high-sensitive electrochemical sensor for determination of ascorbic acid (AA) in the presence of high concentration of Sudan I in food samples. In the first step, we study synthesis and characterization of NiO/NPs with X-ray diffraction (XRD) method. In the second step, application of NiO/NPs describe in the preparation of carbon-paste electrode modified with (9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboximido)-4-ethylbenzene-1,2-diol (DEDED) as a high-sensitive and selective voltammetric sensor for determination of AA and Sudan I. The electrocatalytic oxidation of AA at the modified electrode was investigated by cyclic voltammetry, chronoamperometry and square wave voltammetry (SWV). For the mixture containing AA and Sudan I, the peaks potential was well separated from each other. Their square wave voltammetrics peaks current increased linearly with their concentration at the ranges of 0.01–600 and 0.5–1,000 μM, with the detection limits of 0.006 and 0.2 μM, respectively. Finally, the proposed method was also examined as a selective, simple, and precise electrochemical sensor for the determination of AA and Sudan I in real samples such as fruit juices, fresh vegetable juice, chilli sauce and tomato sauce.     

Simultaneous Determination of TBH<Subscript>2</Subscript>Q and BHA Antioxidants in Food Samples Using Eosin Y Film Modified Electrode

A glassy carbon electrode (GCE) was modified with eosin Y that was electrodeposited on GCE via continuous cycling between ??1.6 and 1.5 V (vs Ag/AgCl). This electrode was characterized by scanning electron microscopy and electrochemical impedance spectra. The resulting electrode exhibited excellent electrocatalytic activity toward the oxidation of butylated hydroxyanisole (BHA) and tert-butyl hydroquinone (TBH₂Q); in addition, the oxidation products of BHA and TBH₂Q were found to be the same, which was studied by CV and in situ FT-IR spectroelectrochemistry. Under the optimized condition, the oxidation peak currents were linear to BHA/TBH₂Q in the range from 0.10 to 7.00 μg mL^?1 with the detection limits of 0.01 μg mL^?1 (S/N?=?3) for BHA and 0.015 μg mL^?1 (S/N?=?3) for TBH₂Q, respectively. Moreover, the reproducibility and repeatability of the electrode were determined. The proposed method was successfully applied in the simultaneous determination of BHA and TBH₂Q in several edible oil samples, and satisfactory results when compared with those obtained using high-performance liquid chromatography.     

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 behaviour of Sudan I at Fe3O4 nanoparticles modified glassy carbon electrode and its determination in food samples

In this work, a simple and sensitive electrochemical method was developed to determine Sudan I based on magnetic Fe₃O₄ nanoparticles modified glassy carbon electrode using cyclic voltammetry and differential pulse voltammetry. The sensor exhibited an obviously electrocatalytic activity towards the oxidation of Sudan I, which can be confirmed by the increased oxidation peak current and the decreased oxidation peak potential when compared with the bare GCE. The determination conditions, such as pH, modifier amount, accumulation time and accumulation potential, were optimised. And some kinetic parameters were calculated. Under the optimum experimental conditions, the oxidation current of Sudan I was proportional to its concentration from 0.01 to 1 μM and 1 to 20 μM. The detection limit was estimated to be 0.001 μM (S/N = 3). The developed method was successfully applied to determine Sudan I content in food samples with satisfactory 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.     

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.     

Enhanced-Oxidation and Highly Sensitive Detection of Tartrazine in Foodstuffs via New Platform Based on Poly(5-Sulfosalicylic Acid)/Cu(OH)<Subscript>2</Subscript> Nanoparticles

Poly(5-sulfosalicylic acid) (PSSA)/Cu(OH)₂ nanoparticle–graphite (Gr) nanocomposite-modified glassy carbon electrode (PSSA/Cu(OH)₂–Gr/GCE) was utilized for sensitive determination of tartrazine using squarewave voltammetry (SWV). The structure of the nanocomposite was investigated by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM(. PSSA/Cu(OH)₂–Gr/GCE exhibited an enhancement in anodic peak current, electron transfer kinetics, effective surface area, and reactive sites and indicated good electrocatalytic activity toward the oxidation of tartrazine. The as-proposed modified electrode achieved a satisfactory dynamic range between the anodic peak current and the concentration of tartrazine at two concentration ranges of 0.01–0.6 and 0.6–10 μmol/L, and the detection limit was obtained to be 8 nmol/L (S/N = 3). The resulting sensor was successfully used to determine tartrazine in real samples such as candy, softdrink, orange juice powder, banana-flavored jelly powder, and candy-coated chocolate.     

A novel potentiometric pH electrode based on sulfated natural Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and analytical application in food samples

A novel solid state potentiometric pH electrode based on sulfated natural Fe₃O₄ silicone was fabricated. The optimum potentiometric performances such as Nernstian response, response time, selectivity, life-time and reproducibility of pH electrodes were investigated by using a computer-controlled potentiometric device. Moreover, the potentiometric performance of the solid state pH electrodes was studied with different mixtures sulfated natural Fe₃O₄, silicone and graphite powder. The best potentiometric behavior of proposed pH electrode was obtained with a composition of 20% (w/w) sulfated natural Fe₃O₄, 40% (w/w) graphite powder and 40% (w/w) silicone. The sub-Nernstian response for pH electrode was exhibited with a slope of 30.8?±?1.4 mV/pH (r?=?0.9963) from pH 2 to pH 12. In addition, the dynamic response time was found as 10 s in acidic medium and further the proposed pH electrode can be used for at least 1 year without any significant slope of the pH–potential curve. The selectivity coefficient of pH electrode was interpreted according to fixed interference method in the presences of Na⁺, Li⁺, K⁺, NH₄⁺, SO₄^2?, CH₃COO^? and NO₃^? ions. The reproducibility of pH electrode was calculated in pH 4 and pH 6 phosphate buffers and it was found as 0.24 RSD (%) and 0.27 RSD (%) respectively. The proposed pH electrode was used to determine of pH in acid?bases titration compared with glass pH electrode and is highly stable in corrosive systems including HF solution. Terminally, the pH value was successfully determined in some soft drinks and milk samples by proposed solid state pH electrode at 95% confidence level with satisfactory agreement compared with glass pH electrode.     

Electrochemical Determination of Vitamin B-12 in Food Samples by Poly(2,2′-(1,4-phenylenedivinylene) Bis-8 hydroxyquinaldine)/Multi-Walled Carbon Nanotube-Modified Glassy Carbon Electrode

Poly(2,2′-(1,4-phenylenedivinylene) bis-8-hydroxyquinaldine)/multi-walled carbon nanotube-modified glassy carbon electrode (poly(PBHQ)/MWCNTs/GCE) was developed and applied for the electrochemical estimation of vitamin B-12 (VB-12). Compared to multi-walled carbon nanotube-modified glassy carbon electrode, well-defined redox peaks were observed in phosphate buffer solution at pH 2.5. In contrast with the ill-defined redox peaks observed with unmodified glassy carbon electrode surfaces. The poly(2,2′-(1,4-phenylenedivinylene) bis-8-hydroxyquinaldine-based electrode displayed a good linear range of 0.1 to 10 μM VB-12 with a low detection limit of 0.01 μM. To further study the practical applicability of the proposed sensing procedure, the estimation of real samples was employed with satisfactory consequences. In addition, MWCNTs were used as sorbent for solid phase extraction (SPE) of vitamin B-12 from cereal food samples. Solid phase extraction parameters, such as the amount of MWCNTs, sample volume, pH, and type and amount of the eluent, were optimized.     

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 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 %.     

Optimization of UV irradiation conditions for the vitamin D<Subscript>2</Subscript>-fortified shiitake mushroom (<Emphasis Type="Italic">Lentinula edodes</Emphasis>) using response surface methodology

The aim of this study was to investigate the optimal conditions to process vitamin D₂-fortified shiitake mushrooms through UV irradiation for industrial processing. Response surface methodology was used to identify the optimum conditions of the following highly influential factors on vitamin D₂ synthesis: temperature, UV dosage, and moisture content. The optimal conditions of those variables were 40.56 °C, 36.27 kJ/m², and 80.46%, respectively, and UV dosage was the most effective variable. The amount of vitamin D₂ obtained under the optimal conditions was 29.87 ± 1.38 μg/g (dry mass: DM) which was well matched with the predicted value of 32.33 μg/g DM. The effects on the texture and color of shiitake mushrooms were also evaluated after the fortification process under the optimal conditions, and no adverse effects were observed compared to those of fresh shiitake mushrooms.     

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.     

Application of Ionic Liquid-Based Ultrasound-Assisted Extraction of Five Phenolic Compounds from Fig (<Emphasis Type="Italic">Ficus carica</Emphasis> L.) for HPLC-UV

Ionic liquid-based ultrasonic-assisted extraction (IL-UAE) was successfully developed to extract the known phenolics gallic acid, chlorogenic acid, rutin, psoralen, and bergapten present in the leaves, pulps, and peels of Ficus carica L. In this work, the proposed method was evaluated in comparison with regular ultrasonic-assisted extraction in which methanol was the extractant and exhibited higher efficiency. Moreover, ionic liquids with different cations were investigated and 1-butyl-3-methylimidazole hexafluorophosphate solution was selected as the optimal extractant at concentration of 1.0 mol L^?1. The corresponding extraction parameters including extraction solvent, the concentration of [BMIM][PF₆], solid–liquid ratio (g mL^?1), ultrasonic extraction time, and extraction temperature were optimized. The phenolics were then determined by high-performance liquid chromatography (HPLC). Under the optimized conditions, the content of gallic acid, chlorogenic acid, rutin, psoralen, and bergapten in leaves, pulps, and peels of F. carica L. was 12.67–37.16, 14.75–90.07, 107.91–222.37, 2.59–67.83, and 1.99–20.21 μg/0.1 g, respectively. This study suggests that IL-UAE is a rapid, simple, and green preparation technique.     

Potentiometric Determination of Aluminum in Foods, Pharmaceuticals, and Alloys by AlMCM-41-Modified Carbon Paste Electrode

A new chemically modified electrode is constructed by incorporating AlMCM-41 into carbon paste matrix (AlMCM-41-MCPE) and used as a sensitive sensor for detection of aluminum in aqueous and nonaqueous solutions. The rapid exchange kinetics in the membrane results in a near-Nernstian behavior of the modified electrode and makes it a suitable potentiometric sensor for detection of aluminum. A linear response in concentration range from 1.0?×?10^?6 to 1.0?×?10^?1 mol/L (0.027 μg/mL–2.7 mg/mL) was obtained with a detection limit of 4.6?×?10^?7 mol/L for the potentiometric detection of aluminum. Selectivity coefficients of a number of interfering cations have been estimated. The interference from many of the investigated ions is negligible. The AlMCM-41-MCPE is suitable for use in aqueous solution of pH 2–6 and in partially nonaqueous medium. The modified electrode exhibited a fast response time (~8 s), good stability, and an extended lifetime. The developed sensor was used successfully for the determination of Al³⁺ in some alloys, drugs, and food products.     

Sensitive voltammetric determination of Sudan I in food samples by using gemini surfactant–ionic liquid–multiwalled carbon nanotube composite film modified glassy carbon electrodes

A novel modified electrode was fabricated, which comprised of hydrophobic ionic liquid (i.e. trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide, [P_6,6,6,14][NTf₂]), multiwalled carbon nanotubes (MWNTs) and cationic genimi surfactant (i.e. C₁₂H₂₅N(CH₃)₂–C₄H₈–N(CH₃)₂C₁₂H₂₅Br₂, C₁₂–C₄–C₁₂). Cyclic voltammetry and linear sweep voltammetry were used to investigate the electrochemical behaviour of Sudan ?. The components showed good synergic interaction in sensing Sudan ?, thus the modified electrode presented higher sensitivity. After optimising the experimental conditions, the anodic peak current of Sudan I was linear to its concentration in the range of 0.05–2 μmol l⁻¹, and the detection limit was 0.03 μmol l⁻¹ in pH 4.5 potassium biphthalate buffer with acetonitrile. The modified electrode had good stability and repeatability. It was applied to the detection of Sudan ? in hot chilli powder and ketchup samples, and the recovery was acceptable.     

Rapid Analysis of Multiple Sudan Dyes in Chili Flakes Using Surface-Enhanced Raman Spectroscopy Coupled with Au–Ag Core-Shell Nanospheres

Sudan dyes are often illegally added as colorants into a variety of foodstuffs and have been tied to many food safety issues. In this study, surface-enhanced Raman spectroscopy (SERS) coupled with Au–Ag core-shell nanospheres (Au@Ag) was applied to analyze standard solutions of Sudan I–IV and Sudan dyes in chili flakes. With the use of 90 ± 5 nm Au@Ag (Au seed 20 ± 2 nm) as SERS substrate, the lowest detectible concentrations for Sudan I and II were 0.10 mg/L, for Sudan III was 0.08 mg/L, and for Sudan IV was 0.2 mg/L. The use of principal component analysis (PCA) could successfully classify different Sudan dyes based upon the SERS spectra of their standard solutions. For chili flakes, the use of acetonitrile as extraction solvent led to an overall higher sensitivity for analysis of Sudan dyes with SERS method compared to that of methanol, ethanol, and n-hexane. The lowest detectible concentrations for Sudan I–III in chili flakes were 1 mg/kg and for Sudan IV was 2 mg/kg, which were about ten times as much as that for their standard solutions due to the interference of non-target compounds from sample matrices. Partial least squares (PLS) models developed for quantitative analyses showed relatively high linear correlation between the actual and predicted amounts of Sudan dyes in chili flakes (R ² _cv = 0.869–0.959). The results showed great potential of applying Au@Ag as SERS substrate for qualitative and quantitative analysis of Sudan I–IV with simplified sample preparation method.