Development of an Aluminium Doped TiO2 Nanoparticles‐modified Screen Printed Carbon Electrode for Electrochemical Sensing of Vanillin in Food Samples

A new chemically modified electrode based on titanium dioxide nanoparticles (TiO₂‐NPs) has been developed. Aluminium was incorporated into the TiO₂‐NPs to prepare aluminium doped TiO₂ nanoparticles (Al‐TiO₂‐NPs). Aluminium doped TiO₂ nanoparticles‐modified screen printed carbon electrode (Al‐TiO₂‐NPs/SPCE) was employed as easy, efficient and rapid sensor for electrochemical detection of vanillin in various types of food samples. Al‐TiO₂‐NPs were characterized by energy‐dispersive X‐ray (EDX), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) and analyses showing that the average particle sizes varied for the Al‐NPs (7.63 nm) and Al‐TiO₂‐NPs (7.47 nm) with spherical crystal. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used to optimize the analytical procedure. A detection limit of vanillin was 0.02 μM, and the relative standard deviation (RSD) was 3.50 %, obtained for a 5.0 μM concentration of vanillin. The electrochemical behaviour of several compounds, such as vanillic acid, vanillic alcohol, p‐hydroxybenzaldehyde and p‐hydroxybenzoic, etc., generally present in natural vanilla samples, were also studied to check the interferences with respect to vanillin voltammetric signal. The applicability was demonstrated by analysing food samples. The obtained results were compared with those provided by a previous method based on liquid chromatography for determination of vanillin.     

Rapid and Selective Determination of Vanillin in the Presence of Caffeine,its Electrochemical Behavior on an Au Electrode Electropolymerized with 3‐Amino‐1,2,4‐triazole‐5‐thiol

Electrochemical oxidation of vanillin (VAN) in the presence of caffeine (CAF) was studied on a gold (Au) electrode modified with 3‐amino‐1,2,4‐triazole‐5‐thiol (ATT) film by using differential pulse voltammetry (DPV) and cyclic voltammetry (CV) method. The formation of the ATT film on the Au electrode surface was characterized by the CV, fourier transform infrared spectroscopy (FTIR) and impedance spectroscopy (EIS) methods. A single irreversible oxidation peak of the VAN was obtained by using the CV method. The determination of VAN in the presence of CAF was carried out at pH 4 in Britton Robinson buffer (BR) by the DPV method. Under the optimal conditions, the oxidation peak current was proportional to the concentration of VAN in the range of 1.1 μM to 76.4 μM in the presence of CAF with the correlation coefficient of 0.997 and the detection limit of 0.19 μM (S/N=3). The selective determination of VAN in a commercial coffee sample was carried out with satisfactory results on the ATT‐Au modified electrode.     

Supported liquid membrane-modified piezoelectric flow sensor with molecularly imprinted polymer for the determination of vanillin in food samples

An on-line supported liquid membrane-piezoelectric detection system, based on a molecularly imprinted polymer (SLM-QCM-MIP) manifold, has been developed and applied to the quantitative determination of vanillin in food samples. The analyte is extracted from a donor phase into the hydrophobic membrane, and then back extracted into a second aqueous phase used as the acceptor solution. The quantification of vanillin was performed using a quartz crystal microbalance modified with a molecularly imprinted polymer (MIP). The method shows a linear range between 5 and 65 μM, with a relative standard deviation of ±4.8% (at 5 μM). The method was validated by analysing food samples and comparing the results with an SLM based on spectrophotometric quantification.     

Voltammetric Determination of Neotame by Using Chitosan/Nickelnanoparticles/Multi Walled Carbon Nanotubes Biocomposite as a Modifier

A selective and simple biosensor was prepared by immobilizing chitosan/nickelnanoparticles/multi-walled carbon nanotubes biocomposite on the glassy carbon electrode surface for voltammetric quantification of neotame. The properties and morphology of the modified electrode surfaces were characterized by scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX). Electro oxidation of neotame on this modified surface was examined through cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques. The biocomposite modified surface (Chi/NiNPs/MWCNTs/GCE) proposed in this study showed good electrocatalytic activity for neotame with an improved voltammetric peak current at 1.004 V, unlike the bare glassy carbon electrode (GCE) surface and several other modified surfaces. Under optimum conditions, Chi/NiNPs/MWCNTs/GCE gave linear SWV responses at the range of 2 μM ∼50 μM for neotame with 0.84 μM determination limit. This voltammetric sensor was successfully employed for the quantification of neotame on food samples and showed long-term stability, advanced voltammetric behavior, and good repeatability. Selective, accurate, and precise determination of neotame highlight the importance of this electrode in monitoring the control of food additives and ensures attract a great deal of attention.     

Simultaneous Detection of Dopamine and Uric Acid on Indium Tin Oxides Modified with Cost‐effective Gas‐phase Synthesized Single Walled Carbon Nanotubes

Cost‐effective gas‐phase synthesized single walled carbon nanotubes (SWCNTs) were first employed for the surface modification of indium tin oxides (ITO) via electrostatic coating of poly‐l‐lysine (PLL). Compared with control substrates of bare ITO and SWCNT‐PLL‐slide glasses, SWCNT‐PLL‐ITO, with high catalytic properties associated with large surface areas, showed significant improvement of electro catalytic activity toward the oxidation of dopamine (DA) and uric acid (UA). The cyclic voltammetric (CV) peak separation of oxidation for both DA and UA was estimated to be ∼ 0.13 V, which renders them capable of simultaneously detecting DA and UA in a mixed solution. The differential pulse voltammetry (DPV) technique was further performed to obtain a linear detection range of DA from 1.0 μM to 100 μM, and a detection limit of 1.0 μM was confirmed in the mixed solution. Furthermore, the practical analytical ability of the method was finally confirmed by selective detection of both DA and UA in human urine samples without any preliminary treatment, implying the feasibility of applying bio‐sensors in a low‐cost manner.     

Simultaneous Determination of Gallic Acid and Folic Acid in Fruit Juice Samples Using Square Wave Voltammetry at Electrochemically Pretreated Carbon Paste Electrode

An efficient sensor was developed for the simultaneous determination of gallic and folic acid in juice samples using an electrochemically pretreated carbon paste electrode. The electrode was characterized by CV and EIS. The electrochemical behavior of GA and FA was evaluated by CV and SWV. The electrode exhibited high electrocatalytic activity towards GA and FA due to high surface area. Under the optimized condition, linear plots in the ranges of 0.08–13 μM and 0.1 to 15 μM were obtained for GA and FA, respectively. The proposed method was successful for the simultaneous determination of GA and FA in juice samples with satisfactory recovery.     

Fabrication of Cu−CeO2 Coated Multiwall Carbon Nanotube Composite Electrode for Simultaneous Determination of Guanine and Adenine

A copper nano particles and cerium (IV) oxide modified carbon nanotube based composite on glassy carbon electrode (Cu−CeO₂/MWCNT/GCE) was fabricated for simultaneous determination of guanine and adenine. The surface morphology, chemistry and conductance of the prepared electrodes were characterized by scanning electron microscopy (SEM), energy dispersion X‐ray (EDX), X‐Ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The Cu−CeO₂/MWCNT/GCE improved electrochemical behaviour of guanine and adenine compared to other electrodes. The modified electrode was also used for individual and simultaneous determination of guanine and adenine. Under optimized conditions, the calibration curves were obtained linearly in the range of 0.20 to 6.00 μM for the guanine and 0.10 to 8.0 μM for the adenine by differential pulse voltammetry. The limits of detection of guanine and adenine were calculated as 0.128 and 0.062 μM, respectively. Interferences studies were also performed in the presence of inorganic and organic compounds. Moreover, the determination of guanine and adenine contents were carried out in a calf thymus DNA sample by the developed method with satisfactory results.     

Sensitive Voltammetric Determination of Bisphenol A Based on a Glassy Carbon Electrode Modified with Copper Oxide‐Zinc Oxide Decorated on Graphene Oxide

A highly sensitive and selective chemical sensor was prepared based on metallic copper‐copper oxides and zinc oxide decorated graphene oxide modified glassy carbon electrode (Cu?Zn/GO/GCE) through an easily electrochemical method for the quantification of bisphenol A (BPA). The composite electrode was characterized via scanning electron microscopy (SEM), X‐Ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The electrochemical behavior of BPA in Britton‐Robinson (BR) buffer solution (pH 7.1) was examined using cyclic voltammetry (CV). Under optimized conditions, the square wave voltammetry (SWV) response of Cu?Zn/GO/GCE towards BPA indicates two linear relationships within concentrations (3.0 nmol L^?1?0.1 μmol L^?1 and 0.35 μmol L^?1?20.0 μmol L^?) and has a low detection limit (0.88 nmol L^?1). The proposed electrochemical sensor based on Cu?Zn/GO/GCE is both time and cost effective, has good reproducibility, high selectivity as well as stability for BPA determination. The developed composite electrode was used to detect BPA in various samples including baby feeding bottle, pacifier, water bottle and food storage container and satisfactory results were obtained with high recoveries.     

Rapid Electrochemical Detection of Vanillin in Natural Vanilla

A commercially available and disposable multiwalled carbon nanotube screen‐printed electrode (CNT‐SPE) was employed to detect and determine vanillin compounds in natural vanilla. The voltammetric behaviour of vanillin at the CNT‐SPE is examined and shown to be a sensitive method for quantifying vanillin. Linear calibration for vanillin in the range of 2.5–750 μM was obtained with a detection limit of 1.03 μM and a quantification limit of 3.44 μM. The developed method comprises a simple sample preparation method and a sensitive electrochemical detection for the quantification of vanillin in vanilla pods and is an easy and simple procedure for manufacturers and consumers.     

Novel Electrochemically Treated Graphite Pencil Electrode Surfaces for the Determination of Trace α‐Naphthol in Water Samples

An electrochemically treated graphite pencil electrode (PGPE) has been simply prepared for trace level determination of α‐naphthol. The pretreatment of GPE surfaces is conducted in 0.8 M NaOH by cycling the potential between +1.3 and +1.9 V for 50 CV segments at a scan rate of 100 mV s^?1. The influence of the pretreatment is studied extensively, and optimum conditions are obtained. Linear sweep anodic stripping voltammetry (LSASV) is used for the determination of α‐naphthol. Based on the constructed calibration curve, a linear range of 0.01 μM to 2.0 μM with a detection limit of 1.5 nM (S/N=3) is obtained. The results reveal that the electrochemical treatment of the GPE surface improves its electrochemical catalytic activity with reference to surfaces of the non‐treated GPE. The present method is applied for the determination of trace α‐naphthol in real water samples.     

PoPD Modified ITO Based Capacitive Immunosensor for Sulphathiazole

A capacitive immunosensor for determination of sulphathaizole (STZ) has been developed on polymer coated indium tin oxide glass chip (ITO). The immunosensor chip was fabricated by polymerizing, ortho‐ phenylenediamine (o PD) on ITO followed by surface modification with anti‐sulphathiazole antibody. The developed immunosensor chip was characterized by using Atomic force microscopy (AFM), Cyclicvoltammetry (CV) and Electrochemical impedance spectroscopy (EIS). The capacitive measurement of the developed immunosensor was performed by using EIS in spiked drinking water and milk. The developed sensor showed liner detection range 0.1‐100 μgL⁻¹for STZ with a limit of detection 0.01 μgL⁻¹ in water with recovery between 95–106 %. The biosensor showed excellent selectivity and storage stability upto 4 weeks when preserved at 4 °C.     

Electrochemical Synthesis of Shape-controlled Cu−Ni Nanocomposite and its Application for Nonenzymatic Glucose Sensing at Nanomolar Level

The electrodeposition method was firstly applied to obtain uniform cube-shaped copper nanoparticles on conductive glass (ITO), and then a layer of tiny nickel nanoparticles. A bimetallic composite electrode (Cu−Ni/ITO), characterized by TEM, XPS and XRD, was prepared to construct the non-enzyme electrochemical glucose sensor with high catalytic activity. The catalytic performance of Cu−Ni/ITO had been greatly improved, probably due to the synergistic bimetallic catalysis effect. The electrode had a satisfactory linear response in the range of 2.5×10⁻⁷ M to 2.6×10⁻³ M, with detection limit as low as 67 nM. Besides, Cu−Ni/ITO had good anti-interference ability and reproducibility, indicating the promising application for glucose detection in practical samples.     

Simultaneous spectrophotometric kinetic determination of four flavor enhancers in foods with the aid of chemometrics

A sensitive kinetic spectrophotometric method was developed for the determination of four flavor enhancers--maltol, ethyl maltol, vanillin, and ethyl vanillin--in food samples. The method was based on the reduction of iron(III) by the four analytes in a sulfuric acid medium (0.012 mol/L), and the subsequent interaction of iron(II) with hexacyanoferrate(III) to form the strongly colored Prussian blue complex, which exhibited an absorption maximum at 800 nm. The optimized method had linear calibrations over the concentration ranges of 0.2-2.8 mg/L for maltol, ethyl maltol, and vanillin, as well as 0.2-1.8 mg/L for ethyl vanillin; the corresponding detection limits were 0.07, 0.07, 0.06, and 0.06 mg/L, respectively. Calibration models were constructed from the original and first-derivative spectral data with the use of partial least-squares (PLS) and principal component regression chemometrics methods. Ultimately, the proposed analytical procedure was successively applied for the determination of the four compounds in commercial food samples with the use of a PLS calibration based on the first-derivative spectral data. The results were comparable with those from a reference HPLC method.     

气相色谱-三重四极杆质谱法同时测定巴氏杀菌乳中9种香精成分

建立了气相色谱-三重四极杆质谱（GC-MS/MS）同时检测巴氏杀菌乳中9种香精成分（二氢香豆素、香兰素、香豆素、乙基香兰素、甲基香兰素、7-甲基香豆素、7-甲氧基香豆素、7-乙氧基-4甲基香豆素和环香豆素）的分析方法。巴氏杀菌乳样品用乙醇溶液萃取,低温涡旋离心,取上清液过0.22 μm滤膜,以DB-5MS色谱柱分离,在MRM模式下测定,基质曲线外标法定量。实验结果表明,9种香精成分在1~200 μg/L范围内呈良好线性,线性相关系数（R²）均大于0.997,方法的检出限为0.002~0.1 μg/kg,定量限为0.001~2 μg/kg,平均回收率为90.3%~110.6%,日内、日间精密度均小于10%。该方法前处理简单快速,检测准确度和灵敏度高,可用于巴氏杀菌乳中9种香精成分的同时检测。     

Tailor‐made ion‐imprinted polymer based on functionalized graphene oxide for the preconcentration and determination of trace copper in food samples

A tailor‐made Cu(II) ion‐imprinted polymer based on large‐surface‐area graphene oxide sheets has been synthesized for the preconcentration and determination of trace copper from food samples by solid‐phase extraction. Attributed to the ultrahigh surface area and hydrophilicity of graphene oxide, the Cu(II) ion‐imprinted polymer prepared by the surface ion‐imprinting technique exhibited a high binding capacity and a fast adsorption rate under the optimized experimental conditions. In the static adsorption experiments, the maximum adsorption capacity of Cu(II) ion‐imprinted polymer is 109.38 mg/g at 25°C, which is much higher than that of the nonimprinted polymer (32.12 mg/g). Meanwhile, the adsorption is very rapid and equilibrium is reached after approximately 30 min. The adsorption mechanism is found to follow Langmuir adsorption model and the pseudo‐second‐order adsorption process. The Cu(II) ion‐imprinted polymer was used for extracting and detecting Cu(II) in food samples combined with graphite flame atomic adsorption spectrometry with high recoveries in the range of 97.6–103.3%. The relative standard deviation and limit of detection of the method were evaluated as 1.2% and 0.37 μg/L, respectively. The results showed that the novel absorbent can be utilized as an effective material for the selective enrichment and determination of Cu(II) from food samples.     

Two-layered Au@Ag Bimetallic Nanocomposites-poly (L-Met) Platform for Highly Sensitive Chlorpheniramine Maleate Detection

The two-layered bimetallic Au@Ag and poly(L-methionine) (Au@Ag/p-L-met) sensor was newly developed for the electrochemical determination of chlorpheniramine maleate (CPM). After electropolymerization of L-met, bimetallic surfaces were prepared by electrodeposition of Au@Ag nanoparticles on the p-L-met/PGE. The surface characterization was carried out by scanning electron microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX), Cyclic Voltammetry (CV) and Electrochemical impedance spectroscopy (EIS). The sensor shows good electrocatalytic activity, high sensitivity, wide linear range (0.87–600.0 μM) and a low detection limit (0.26 μM) by using Differential pulse voltammetry (DPV). The sensor was used to determine CPM in pharmaceutical samples with satisfactory results.     

Determination of aluminium,copper, iron and manganese in biological and other samples as 8-quinolinol complexes by high-performance liquid chromatography with electrochemical and spectrophotometric detection

A range of methods based on reverse-phase high-performance liquid chromatography is described for determining Al, Cu, Fe and Mn. The simplest method for determining Fe, Cu and Al involves direct formation and separation of the 8-quinolinol complexes on the column, with 1:1 acetonitrile/water containing 5 × 10^?3 M 8-quinolinol, 0.4 M potassium nitrate and 0.02 M acetate buffer (pH 6.0) as the mobile phase, followed by electrochemical detection at ?0.5 V vs. Ag/AgCl and/or spectrophotometric detection at 400 nm. Electrochemical detection enables < 2 ng Cu and < 1 ng Fe to be quantified for injection volumes of 20 μ1. Spectrophotometric detection allows simultaneous determinations of Al, Cu and Fe with lower sensitivity. The method is applied to the determination of Cu, Fe and Al in bovine liver and oyster tissue. Down to 1 ng of manganese (in the 20 μ1 injected) can be determined in biological samples by liquid chromatography with a mobile phase containing 1 mM Tris buffer (pH 8.8) after injection of an externally prepared 8-quinolinol complex. Preconcentration on Sep-Pak cartridges after dichloromethane extraction is used for the determination of low concentrations of iron in water. A sensitive determination of aluminium based on detection at 254 nm is also reported.     

Platinum Nanoparticles/Poly(isoleucine) Modified Glassy Carbon Electrode for the Simultaneous Determination of Hydroquinone and Catechol

A new electrochemical sensor based on Poly(Isoleucine) modified glassy carbon electrode decorated with platinum nanoparticles (Pt/Poly(Isoleucine)/GCE) was developed for sensitive individual and simultaneous determination of hydroquinone (HQ) and catechol (CC). Scanning electron microscopy (SEM), Electrochemical impedance spectroscopy (EIS), Cyclic voltammetry (CV) and Differential pulse voltammetry (DPV) were performed in order to characterize the Pt/Poly(Isoleucine)/GCE nanocomposite. For simultaneous determination of HQ and CC, Pt/Poly(Isoleucine)/GCE showed wide linear range between the 0.01–100.0 μM. The detection limits were 0.006 μM for HQ and 0.005 μM for CC. The Pt/Poly(Isoleucine)/GC electrode exhibited good sensitivity and reliability in the simultaneous electroanalysis of two isomers in PBS of pH 7.5. The modified electrode was used to detect the isomers in naturel samples.     

Selective Voltammetric Detection of Uric Acid in the Presence of Ascorbic Acid at Well‐Aligned Carbon Nanotube Electrode

The voltammetric behaviors of uric acid (UA) and L ‐ascorbic acid (L ‐AA) were studied at well‐aligned carbon nanotube electrode. Compared to glassy carbon, carbon nanotube electrode catalyzes oxidation of UA and L ‐AA, reducing the overpotentials by about 0.028 V and 0.416 V, respectively. Based on its differential catalytic function toward the oxidation of UA and L ‐AA, the carbon nanotube electrode resolved the overlapping voltammetric response of UA and L ‐AA into two well‐defined voltammetric peaks in applying both cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which can be used for a selective determination of UA in the presence of L ‐AA. The peak current obtained from DPV was linearly dependent on the UA concentration in the range of 0.2 μM to 80 μM with a correlation coefficient of 0.997. The detection limit (3δ) for UA was found to be 0.1 μM. Finally, the carbon nanotube electrode was successfully demonstrated as a electrochemical sensor to the determination of UA in human urine samples by simple dilution without further pretreatment.     

微波消解一氢化物原子荧光光谱法测定罐头食品中锡

为建立微波消解-氢化物原子荧光光谱法测定罐头食品中锡含量的方法。样品在HNO3＋HC1或HN03＋HCl＋H2O2体系中经微波消解处理后,以硫脲-抗坏血酸混合液作预还原剂,用氢化物原子荧光光谱法测定罐头食品中锡。结果表明,在优化的条件下,锡质量浓度在0～100μg／L范围内线性关系良好,相关系数为0．9998,方法最低检出限为0．067mg／kg,加标回收率在99．7％～108．3％之间,方法变异系数为2．67％（n=6）。该法具有准确度高、精密度好、灵敏快速且安全环保等优点,适用于罐头食品中锡的测定。