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.     

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 Polypropylene Amine Dendrimers (POPAM)-Grafted MWCNTs Hybrid Materials as a New Sorbent for Solid-Phase Extraction and Trace Determination of Gold(III) and Palladium(II) in Food and Environmental Samples

A new method which utilizes a polypropylene amine dendrimers (POPAM)-grafted multi-walled carbon nanotubes (MWCNTs) hybrid materials as an effective sorbent in solid-phase extraction has been developed for separation and preconcentration of Au(III) and Pd(II) trace levels in food, water and soil samples. The optimum experimental conditions such as pH, flow rates, type, concentration, and volume of the eluent for elution of gold and palladium ions, breakthrough volume, and effect of potentially interfering ions on separation and determination of these noble metals were investigated. The extraction recoveries for the mentioned noble metals were greater than 98 % and the limits of detection were 0.08 and 0.12 ng mL^?1 for gold and palladium, respectively. The relative standard deviations of the method were less than 4 % for eight separate column experiments for determination of 5.0 μg of gold and palladium ions. The adsorption capacity of the modified MWCNT was 92 mg g^?1 for gold and 74 mg g^?1 for palladium on POPAM-grafted MWCNTs. Validation of the suggested method was performed by analyzing certified reference materials. Finally, the proposed method was applied for determination of gold(III) and palladium(II) in real samples, including fish, shrimp, water, and soil.     

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.     

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.     

A Miniaturized Preconcentration Method Based on Dispersive Liquid–Liquid Microextraction for the Spectrophotometric Determination of Aziridine in Food Simulants

In this work a simple, rapid and sensitive method using dispersive liquid–liquid microextraction (DLLME) combined with UV–Vis spectrophotometry has been developed for the preconcentration and determination of trace amounts of aziridine in food simulants. The method is based on derivatization of aziridine with Folin's reagent (1,2-naphthoquione-4-sulphonic acid) and extraction of color product using DLLME technique. Some important parameters, such as reaction conditions, and type and volume of extraction solvent and disperser solvent were studied and optimized. Under optimum conditions, a linear calibration curve in the range of 2.0–350 ng mL^?1 of aziridine was obtained. Detection limit based on 3S_b was 1.0 ng mL^?1, and the relative standard deviation for 50 ng mL^?1 of aziridine was 2.49c (n?=?7). The proposed method was applied for the determination of aziridine in food simulants.     

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.     

New Voltammetry-Based Analytical Method for Indirect Determination of Procymidone in Brazilian Apples

Procymidone, a potentially carcinogenic and mutagenic pesticide, can contribute to environmental and human contamination when applied to apple crops. In this work, we propose a reliable and sensitive method to determine procymidone in Brazilian apples. The method involves differential pulse (DPV) and square-wave voltammetry (SWV) techniques on a glassy carbon electrode. In a supporting electrolyte solution of 0.5 mol?L^?1 NaOH, procymidone undergoes an irreversible one-electron oxidation at +1.42 V by cyclic voltammetric vs. Ag|AgCl, KCl 3 M reference electrode. The proposed DPV and SWV methods have a good linear response in the 8.00–20.0 mg?L^?1 range, with limits of detection (LOD) of 0.678 and 0.228 mg?L^?1, respectively, in the absence of the matrix. We obtained improved LOD (0.097 mg?L^?1) in the presence of apple matrix and the supporting electrolyte solution. We used three commercial apple samples to evaluate recovery, and we achieved recovery percentages ranging from 94.6 to 110 % for procymidone determinations. We also tested the proposed voltammetric method for reproducibility, repeatability, and potential interferents, and the results were satisfactory for electroanalytical purposes.     

Sensitive determination of nitrite in food samples using voltammetric techniques

A [5,10,15,20-tetrakis (4-methoxyphenyl) porphyrinato] manganese (III)chloride (TMOPPMn(III)Cl)-modified gold electrode sensor was developed for the determination of nitrite in food samples. The developed sensor showed an excellent catalytic activity and stability for nitrite oxidation. Under optimized conditions, nitrite concentration as low as 2.9 × 10⁻⁹ M can be determined in various food samples using the developed sensor. Effect of common interfering ions have been investigated in simulated mixtures containing high levels of interfering ions and the sensor was found to be tolerant against these ions. The determination of nitrite in food samples such as chicken ham, sausage and pickled vegetables with the proposed sensor was in good agreement with those obtained by standard spectrophotometric method.     

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.     

Sensitive and Efficient Electrochemical Determination of Kojic Acid in Foodstuffs Based on Graphene-Pt Nanocomposite-Modified Electrode

A differential pulse voltammetric (DPV) method for the determination of kojic acid was developed. Glassy carbon (GC) electrode was modified with composite nanomaterials of graphene (GR) sheets and platinum (Pt) nanoparticles. Electrochemical behavior of kojic acid on the electrode was studied, which indicated that the nanocomposite-modified electrode could efficiently promote electrocatalytic oxidation of kojic acid based on synergistic effect of excellent electrical conductivity and high catalytic activity of GR and Pt. A rapid, sensitive, and simple electrochemical method was then developed for determination of kojic acid using the constructed electrode. Under the optimized conditions, the oxidation peak current exhibited a wide linear range from 0.2 to 1,000 μM towards the concentration of kojic acid with a sensitivity of 139.3 μA mM^?1, and the limit of detection was as low as 0.2 μM. The modified electrode was also used for quantitative analysis of kojic acid in food samples, and the recoveries were between 97.5 and 101.3 %, indicating feasibility of the electrochemical method for kojic acid analysis in routine detection. In view of optimization and validation results as well as applicability to real samples, this method could be considered as a good alternative for routine analysis of kojic acid in foodstuffs.     

Determination of Iron Species in Samples of Iron-Fortified Food

The paper presents the determination of iron forms in food products. The procedure of sample extraction was developed and optimized, preserving the content of particular forms of iron. The colorimetric method using 2,2′-bipirydyl (measurements at 520 nm) was applied in Fe(II) determinations, while in Fe(III) determinations, the colorimetric method with potassium thiocyanate (measurements at 470 nm) was applied. The total content of iron was determined by the technique of atomic absorption spectrometry, which allowed for the determination of iron content in organic and inorganic complex compounds. Detection limits of 1 mg kg^?1 were obtained for all determined iron forms, with the precision ranging between 0.7 % and 1.5 % for 10 mg kg^?1 concentration. The optimized analytical procedure was applied in the determinations of iron forms in iron-fortified food products.     

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.     

Main Organic Acids in Rice Wine and Beer Determined by Capillary Electrophoresis with Indirect UV Detection Using 2, 4-Dihydroxybenzoic Acid as Chromophore

A rapid and sensitive analytical method for the determination of main organic acids in wines was developed by capillary electrophoresis (CE) with indirect UV detection. Separation parameters including the pH of electrolyte, chromophore, and its concentration were optimized. The results showed that the optimal electrolyte for the separation of organic acids consisted of 10 mmol L^?1 2, 4-dihydroxybenzoic acid (DHBA) at pH 3.6 containing 0.4 mmol L^?1 cetyltrimethlammonium bromide (CTAB). DHBA as chromphore was selected based on the close mobility to the analyte and relatively large molar extinction coefficient. The method showed good linearity with limits of detection (LOD), ranging from 0.5 to 7.5 mg L^?1. The relative standard deviation (RSD) of interday precisions for the peak area and the migration time were less than 7.2 and 0.8 %, respectively. The recoveries of the analyte in Chinese rice wine sample were between 90.3 and 106.9 % with RSD ranging from 1.4 to 8.9 %. The method was successfully applied to the commercial rice wine and beer samples with dilution and filtration.     

A Biosensor Utilizing l-Glutamate Dehydrogenase and Diaphorase Immobilized on Nanocomposite Electrode for Determination of l-Glutamate in Food Samples

Amperometric biosensor utilizing bienzymatic composition consisting of l-glutamate dehydrogenase and diaphorase for the determination of l-glutamate has been developed. Enzymes were immobilized between chitosan layers onto the surface of planar nanocomposite electrodes consisting of multi-walled carbon nanotubes (diameter?=?60–100 nm; length?=?5–15 μm, 95+?% purity). Linear response was obtained from 10 to 3,495 μM in phosphate buffer solution of pH 9.0 and in the presence of enzyme cofactor NAD⁺ (2 mM) and mediator ferricyanide (5 mM). The limit of detection was 5.4 μM, and sensitivity was found to be 28 nA μM^?1 cm^?2. The biosensor showed a short response time (within 60 s), good storage (no loss of activity for at least 3 months), and operational (response ability above 90 % after 7 days since its first use) stability. Finally, the results obtained from measurements of the food samples were compared with those obtained with an enzymatic–spectrophotometric method and correlated well. Analytical performance of the biosensor indicated that the bienzyme system utilizing diaphorase as a secondary enzyme could be a general basis for other biosensors based on NAD⁺-dependent dehydrogenases.     

A New and Fast HPLC Method for Determination of Rutin, Troxerutin, Diosmin and Hesperidin in Food Supplements Using Fused-Core Column Technology

A new and fast high-performance liquid chromatography (HPLC) method using fused-core column for separation of rutin, troxerutin, diosmin, and hesperidin has been developed and used for determination of these flavonoids in food supplements. Efficient separation of flavonoids and internal standard methylparaben was achieved on the fused-core column Ascentis Express RP-Amide (100?×?3.0 mm), particle size 2.7 μm, with mobile phase acetonitrile/water solution of acetic acid pH?3 (30:70, v/v) at a flow rate of 1.0 mL?min^?1 and at temperature 50 °C. The detection wavelengths were set at 283 nm for hesperidin and at 255 nm for rutin, troxerutin, diosmin, and internal standard methylparaben. Under the optimal chromatographic conditions, good linearity with correlation coefficients in the range (r?=?0.9991–0.9998; n?=?7) for all flavonoids was achieved. Commercial samples of food supplements were extracted with 100 % dimethyl sulfoxide using ultrasound bath for 10 min and then diluted to methanol. A 5-μL sample volume of the filtered solution was directly injected into the HPLC system. Accuracy of the method defined as a mean recovery of flavonoids from food supplement matrix was in the range 96.2–104.4 % for all flavonoids. The intraday method precision was satisfactory, and relative standard deviations of sample analysis including preparation and determination of different food supplements were in the range 0.5–3.5 % for all flavonoids. The developed method has shown high sample throughput during sample preparation process, modern separation approach, and short time (5 min) of analysis.     

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.     

Assessment of the dietary intake of propylene glycol in the Korean population

An improved method for the analysis of propylene glycol (PG) in foods using a gas chromatography-flame ionisation detector (GC-FID), with confirmation by GC-MS, was validated by measuring several analytical parameters. The PG concentrations in 1073 products available in Korean markets were determined. PG was detected in 74.1% of the samples, in a concentration range from the limit of detection (n.d., 0.39 μg ml^?1) to 12,819.9 mg kg^?1. The Korea National Health and Nutrition Examination Survey (KNHANES) 2011–2013 reported the mean intake levels of PG from all sources by the general population and consumers were 26.3 mg day^?1 (0.52 mg kg^?1 day^?1) and 34.3 mg day^?1 (0.67 mg kg^?1 day^?1), respectively. The 95th percentile intake levels of the general population and consumers were 123.6 mg day^?1 (2.39 mg kg^?1 day^?1) and 146.3 mg day^?1 (2.86 mg kg^?1 day^?1), respectively. In all groups of the general population, breads were the main contributors to the total PG intake. These reports provide a current perspective on the daily intake of PG in the Korean population.     

Monitoring of Zn(II), Cd(II), Pb(II) and Cu(II) During Refining of Some Vegetable Oils Using Differential Pulse Anodic Stripping Voltammetry

In this study, a novel approach has been developed using differential pulse anodic stripping voltammetry (DPASV) for the simultaneous determination of Zn(II), Cd(II), Pb(II) and Cu(II) in edible oils at hanging mercury drop electrode. The microwave digestion of oil samples was carried out with concentrated HNO₃ and H₂O₂. KNO₃ was used as a supporting electrolyte. The experimental conditions optimized such as deposition time, stirring rate and size of mercury drop were 300 s, 600 rpm and 10 mm², respectively. The method was applied to quantify Zn(II), Cd(II), Pb(II) and Cu(II) in crude and refined hazelnut, corn, sunflower and olive oils. During refining of different vegetable oils, the removal efficiencies of Zn(II), Cd(II), Pb(II) and Cu(II) were calculated as 98.20–99.91, 98.50–99.90, 95.26–99.76 and 95.93–99.92 %, respectively. The limits of detection for Zn(II), Cd(II), Pb(II) and Cu(II) were 2.1?×?10^?8, 8.7?×?10^?10, 7.1?×?10^?9 and 3.4?×?10^?9 and the limits of quantification were 6.8?×?10^?8, 2.9?×?10^?9, 2.3?×?10^?8 and 1.1?×?10^?8 M with linear regression coefficients (R ²) of 0.9930, 0.9928, 0.9893 and 0.9931, respectively. It was observed that the above metals in crude and refined vegetable oils could be determined simultaneously by the DPASV method.     

The application of d-SPE in the QuEChERS method for the determination of PAHs in food of animal origin with GC–MS detection

This paper reports the evaluation of the Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method for the determination of polycyclic aromatic hydrocarbons (PAHs) in food of animal origin with GC–MS detection. Although in the available literature, there is a lot of information about sample preparation method for PAHs determination in food samples, but the QuEChERS method application for PAHs determination in food of animal origin has not been reported as yet. The results showed that the best recovery ratios 72.4–110.8 % with relative standard deviation lower than 10 % for all determined compounds were received for the method with ethyl acetate as an extraction solvent, primary–secondary amine and C₁₈ sorbents and evaporation to dryness and dissolving the residues in the hexane. The limit of quantification ranged from 0.0003 to 0.0030 mg kg^?1 for pyrene and benzo[a]anthracene, respectively. This method was also used for the determination of PAHs in 15 samples of pork ham. In 8 of 15 samples selected, PAHs were identified. It was observed that in 6 cooked ham and one smoked and cooked samples, any PAHs were found. In other samples, which were smoked and roasted, some low concentration of PAHs was detected. In one sample benzo[a]pyrene (0.0015 mg kg^?1), in one sample benzo[b]fluoranthene (0.0015 mg kg^?1) and in one sample chrysene (0.0024 mg kg^?1) were detected. A number of other less harmful PAHs were also determined. There were no exceedances of maximum levels (according to Commission Regulation (EU) No 835/2011) for determined PAHs in any of the analysed samples.