Rapid Sample Screening Method for Authenticity Controlling of Vanilla Flavours Using Liquid Chromatography with Electrochemical Detection Using Aluminium-Doped Zirconia Nanoparticles-Modified Electrode

A rapid and sensitive technique for frauds determination in vanilla flavors was developed. The method comprises separation by liquid chromatography followed by an electrochemical detection using a homemade screen-printed carbon electrode modified with aluminium-doped zirconia nanoparticles (Al-ZrO₂-NPs/SPCE). The prepared nanomaterials (Al-ZrO₂-NPs) were characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). This method allows for the determination of six phenolic compounds of vanilla flavors, namely, vanillin, p-hydroxybenzoic acid, p-hydroxybenzaldehyde, vanillyl alcohol, vanillic acid and ethyl vanillin in a linear range between 0.5 and 25 µg g⁻¹, with relative standard deviation values from 2.89 to 4.76%. Meanwhile, the limits of detection and quantification were in the range of 0.10 to 0.14 µg g⁻¹ and 0.33 to 0.48 µg g⁻¹, respectively. In addition, the Al-ZrO₂-NPs/SPCE method displayed a good reproducibility, high sensitivity, and good selectivity towards the determination of the vanilla phenolic compounds, making it suitable for the determination of vanilla phenolic compounds in vanilla real extracts products.     

Enzyme Inhibition and Chromatographic Techniques: Comparative Studies and Application to Pesticide Residue Analysis

Abstract

The development of enzyme inhibition techniques in relation to pesticide analysis is discussed, along with discussion of (a) principles of thin-layer chromatograph-enzyme inhibition (TLC-EI) technique, (b) general procedures of the technique, (c) the use of enzymes in combination with TLC and colorimetry, and (d) merits and limitations of the techniques. TLC-EI techniques and gas-liquid chromatography are compared based on sensitivity of detection, selectivity, and applicability to pesticide analysis.

The TLC-EI technique is being used and developed further in the Research Laboratories, Health Protection Branch, Ottawa for determination and confirmation of some organophosphorus and carbamate pesticides. Recently, it has been developed to detect methomyl (Lannate^(R)) residues in rapeseeds, oils, and meals.     

Direct Determination of Paracetamol in Environmental Samples Using Screen‐printed Carbon/Carbon Nanofibers Sensor – Experimental and Theoretical Studies

The paper describes the first electrochemical method (differential pulse adsorptive stripping voltammetry, DPAdSV) using a screen‐printed sensor with a carbon/carbon nanofibers working electrode (SPCE/CNFs) for the direct determination of low (real) concentrations of paracetamol (PA) in environmental water samples. By applying this sensor together with DPAdSV, two linear PA concentration ranges from 2.0×10^?9 to 5.0×10^?8 mol L^?1 (r=0.9991) and 1.0×10^?7–2.0×10^?6 mol L^?1 ( r=0.9994) were obtained. For the accumulation time of 90 s, the limit of detection was 5.4×10^?10 mol L^?1. Moreover, the SPCE/CNFs sensor and the DPADSV procedure for PA determination are potentially applicable in field analysis. The process of PA adsorption at the SPCE/CNFs surface was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and theoretical studies. In the theoretical study of the interaction of CNF and PA, the first species was modelled by graphene‐like clusters containing up to 37 rings. It was found that the preferable orientation of PA is parallel to the carbon surface with the binding energy of about ?68 kJ/mol calculated by symmetry‐adapted perturbation theory (SAPT). Both the selectivity and the accuracy of the developed sensor for real sample analysis were also investigated using Polish river and sea samples.     

Anti-Biofouling Electrochemical Sensor Based on the Binary Nanocomposite of Silica Nanochannel Array and Graphene for Doxorubicin Detection in Human Serum and Urine Samples

A disposable and portable electrochemical sensor was fabricated by integrating vertically-ordered silica mesoporous films (VMSF) and electrochemically reduced graphene (ErGO) on a screen-printed carbon electrode (SPCE). Such VMSF/ErGO/SPCEs could be prepared by a simple and controllable electrochemical method. Stable growth of VMSF on SPCE could be accomplished by the introduction of an adhesive ErGO nanolayer owing to its oxygen-containing groups and two-dimensional (2D) planar structure. An outer VMSF layer acting as a protective coating is able to prevent the leakage of the inner ErGO layer from the SPCE surface. Thanks to the electrostatic permselectivity and anti-fouling capacity of VMSF and to the good electroactive activity of ErGO, binary nanocomposites of VMSF and ErGO endow the SPCE with excellent analytical performance, which could be used to quantitatively detect doxorubicin (DOX) in biological samples (human serum and urine) with high sensitivity, good long-term stability, and low sample amounts.     

磁性分子印迹电化学传感法检测痕量奥卡西平

该文以4-乙烯基吡啶和甲基丙烯酸酯为原料制备了一种可用于检测奥卡西平（OXC）的磁性分子印迹 电化学传感器（MNPs－MIP/MCPE）。首先,依据密度泛函数理论（DFT/B3LYP/6－31 + G）计算,实验成功地 筛选和构建出 OXC与功能单体的最佳组合及比例。随后,基于沉淀聚合法合成了能够识别 OXC的磁性分子 印迹膜（MNPs－MIP）,将MNPs－MIP覆于碳糊电极（MCPE）表面制成MNPs－MIP/MCPE。采用差分脉冲伏安 法（DPV）将 MNPs－MIP/MCPE 传感器用于不同浓度 OXC 的测定。结果显示,传感器的峰电流信号随 OXC 浓 度的增大而增大,且OXC分别在5 × 10－8 ～3 × 10－6 mol/L和3 × 10－6 ～1. 5 × 10－4 mol/L浓度范围内与其峰电流 信号呈线性关系,其线性方程分别为：Ip （μA）= 1. 755 + 1. 097c（μmol/L）,相关系数（r）= 0. 999 7 和 Ip （μA）= 0. 131 + 5. 177c（μmol/L）,r = 0. 999 6。OXC的检出限（LOD = 3S/m）为2. 06 × 10－8 mol/L。该传感器成 功用于实际样品中OXC含量的检测,其回收率为99. 4%~101%,相对标准偏差（RSD）为1. 5%～2. 5%。     

甲醛电化学传感器多孔气体扩散电极不同催化层结构与响应性能研究

多孔气体扩散电极的制备是制备甲醛电化学传感器的关键所在, 其中催化层的结构直接影响到传感器的响应性能. 通过柠檬酸三钠还原法合成了纳米金-活性炭、纳米金-碳纳米管催化剂, 制备了甲醛电化学传感器多孔气体扩散电极, 并对电极进行SEM(扫描电子显微镜)物理表征. 在甲醛气体浓度为0.24和0.63 mg/m³时, 电极C具有较好的响应, 在0.1到0.84 mg/m³浓度范围内, 线性方程为y＝10.515x＋4.4049 (R²＝0.9917), 响应时间约80 s. 分析了不同催化剂的气体扩散电极结构与甲醛响应性的关系, 为研制开发性能优良的甲醛电化学传感器奠定了基础.     

Metabolomic Profiling,Antioxidant and Enzyme Inhibition Properties and Molecular Docking Analysis of Antarctic Lichens

The lichen species Lecania brialmontii, Pseudephebe pubescens, and Sphaerophorus globosus are part of the prominent lichenoflora of the Antarctic territory. In this work, we report the metabolomic identification of ethanolic extracts of these species, their antioxidant and cholinesterase enzyme inhibitory activity, and conduct a molecular docking analysis with typical compounds. Eighteen compounds were identified by UHPLC-ESI-QTOF-MS in L. brialmontii, 18 compounds in P. pubescens, and 14 compounds in S. globosus. The content of phenolic compounds was variable among the species, ranging from 0.279 to 2.821 mg AG/g, and all three species showed high inhibition potential on the cholinesterase enzymes. Molecular docking showed important interactions between AChE and BChE with the selected compounds. This study evidences the chemical fingerprint of three species of the order Lecanorales that support the continuation of the study of other biological activities and their potential for medical research.     

电动流动分析和酶抑制法测定池塘水中农药残留折合总量

用电动流动分析和酶抑制法测定池塘水中有机磷和氨基甲酸酯农药残留折合总量。电动流动分析系统由一台自制电渗泵和4个电磁切换阀组成,由计算机编程控制。酶抑制法用面粉酯酶,有机磷和氨基甲酸酯农药作酶抑制剂,底物的酶解产物与显色剂反应,用分光光度计在524 nm检测。有机磷和氨基甲酸酯农药的折合浓度对数线性范围为0.02~0.20 mg/L乐果,检出限为0.01 mg/L乐果,每小时可测24个样品。氨基甲酸酯在80℃完全水解,而有机磷部分水解,据此可判断农药类别。     

Study on the Synthesis of ZnO Nanoparticles Using Azadirachta indica Extracts for the Fabrication of a Gas Sensor

This paper compared the effects of A. indica plant proteins over chemical methods in the morphology of zinc oxide nanoparticles (ZnO NPs) prepared by a co-precipitation method, and ethanol sensing performance of prepared thin films deposited over a fluorene-doped tin oxide (FTO) bind glass substrate using spray pyrolysis technique. The average crystallite sizes and diameters of the grain-sized cluster ZnO NPs were 25 and (701.79 ± 176.21) nm for an undoped sample and 20 and (489.99 ± 112.96) nm for A. india dye-doped sample. The fourier transform infrared spectroscopy (FTIR) analysis confirmed the formation of the Zn–O bond at 450 cm⁻¹, and also showed the presence of plant proteins due to A. indica dye extracts. ZnO NPs films exhibited good response (up to 51 and 72% for without and with A. indica dye-doped extracts, respectively) toward ethanol vapors with quick response-recovery characteristics at a temperature of 250 °C for undoped and 225 °C for A. indica dye-doped ZnO thin films. The interaction of A. indica dye extracts helps to decrease the operating temperature and increased the response and recovery rates of the sensor, which may be due to an increase in the specific surface area, resulting in adsorption of more oxygen and hence high response results.     

基于SnO2气体传感器农药残留的动态检测及定性定量分析

研究了一种快速检测和识别农药敌百虫、乙酰甲胺磷气体新方法,即动态俭测方法：这种方法利用单个SnO2气体传感器而非阵列在方波温度调制的状态下可实现两种农药气体的定性分析,实验结果表明、在0．02Hz的调制频率、250～300℃的温度调制范围,传感器对单一组分的农药残留表现出高的选择性和稳定性;利用FFT频谱和极坐标构建完成对敌百虫和乙酰甲胺磷的定性和定量分析。     

A Novel Electrochemical Sensor for Simultaneous Determination of Hydroquinone,Catechol, and Resorcinol Using a Carbon Paste Electrode Modified by Zn-MOF,Nitrogen-doped Graphite,and AuNPs

In this work, the carbon paste electrode was modified with a composite of a metal-organic framework, nitrogen-doped graphite, and gold nanoparticles and used as an electrochemical sensor for dihydroxybenzene isomers. The morphology and characteristics of the modifiers were found by SEM and FT-IR. Electrochemical techniques showed the specific surface of the electrode to be significantly enhanced. The outcome achieved shows that this novel sensor displays an excellent electro-catalytic activity towards the oxidation of these isomers. The sensor was applied to the simultaneous determination of each three isomers using DPV with a linear response in the concentration range of 5–10⁵ nM.     

Determination of Oxytetracycline with a Gold Electrode Modified by Chitosan-Multiwalled Carbon Nanotube Multilayer Films and Gold Nanoparticles

A molecularly imprinted electrochemical sensor was fabricated based on a gold electrode modified by chitosan-multiwalled carbon nanotube composite (CS-MWCNTs) multilayer films and gold nanoparticles (AuNPs) for convenient and sensitive determination of oxytetracycline (OTC). The multilayer of CS-MWCNTs composites and AuNPs were used to augment electronic transmission and sensitivity. The molecularly imprinted polymers (MIPs) were synthesized using OTC as the template molecule and o-phenylenediamine (OPD) as the functional monomer. They were modified on a gold electrode by electropolymerization. The electrochemical behavior of OTC at the imprinted sensor was characterized by cyclic voltammetry (CV), scanning electron microscopy (SEM), and amperometry. The molecularly imprinted sensor showed high selectivity and excellent stability toward OTC. The linear range was from 3.0 × 10^?8 to 8.0 × 10^?5 mol/L, with a limit of detection (LOD) of 2.7 × 10^?8 mol/L (S/N = 3). The developed sensor showed good recovery in spiked samples analysis.     

Study of Electrooxidation Behavior of Nitrite on Gold Nanoparticles/Graphitizing Carbon Felt Electrode and Its Analytical Application

In this work, a gold nanoparticles/graphitizing carbon felt electrode (AuNPs/GCFE) was fabricated and a disposable sensor was thus fabricated to detect nitrite quickly and conveniently. The kinetic parameters of the electrode were studied in phosphate buffer solution (PBS). Under the optimal conditions, by using cyclic voltammetry, the oxidation peak current was linear with the concentration of nitrite in the range from 1.00 × 10^?6 M to 3.35 × 10^?3 M, with a detection limit of 9.50 × 10^?7 M (3S/k). The influence of various anions on nitrite detection was studied, and the results showed that the fabricated sensor had good specificity toward nitrite.     

Stripping Analysis of As(III) by Means of Screen‐Printed Electrodes Modified with Gold Nanoparticles and Carbon Black Nanocomposite

A novel sensor based on carbon black‐gold nanoparticle nanocomposite modified screen‐printed electrode (CB‐AuNPs/SPE) for the detection of As(III) has been developed. The sensor was prepared modifying the SPE with CB and AuNPs by a drop casting automatable deposition. The As(III) was detected by CB‐AuNPs/SPE using anodic stripping voltammetry, with a high sensitivity (673±6 µA µM^?1 cm^?2) and reaching a LOD of 0.4 ppb. Finally, CB‐AuNPs/SPE has been applied to As(III) trace analysis in drinking water, obtaining satisfactory recovery values (99±9 %).     

Comparative Study of Packed and Capillary Column Chromatography for the Characterization of Vacuum Gas Oils

Gas chromatographic methods are of widespread use in the petroleum industry for assessing petroleum and derivatives quality. The feedstocks for catcracking processes are very sensitive to the n-paraffin contents, which can be accurately determined using capillary column chromatography. Nevertheless, packed column chromatography does have potential advantages, viz. sometimes shorter analysis times, lower costs, higher column capacity, for vacuum gas oil analysis. This paper presents a method for such a determination using a Dexsil-300 packed column. The results obtained (n-alkane contents, carbon number distribution) agree fairly well with those obtained on a 30 m × 0.25 mm DB-1 fused silica capillary column.     

Comparative Study of Phosgene Gas Sensing Using Carbon and Boron Nitride Nanomaterials—A DFT Approach

Phosgene (COCl₂), a valuable industrial compound, maybe a public safety and health risk due to potential abuse and possible accidental spillage. Conventional techniques suffer from issues related to procedural complexity and sensitivity. Therefore, there is a need for the development of simple and highly sensitive techniques that overcome these challenges. Recent advances in nanomaterials science offer the opportunity for the development of such techniques by exploiting the unique properties of these nanostructures. In this study, we investigated the potential of six types of nanomaterials: three carbon-based ([5,0] CNT, C60, C70) and three boron nitride-based (BNNT, BN60, BN70) for the detection of COCl₂. The local density approximation (LDA) approach of the density functional theory (DFT) was used to estimate the adsorption characteristics and conductivities of these materials. The results show that the COCl₂ molecule adsorbed spontaneously on the Fullerene or nanocages and endothermically on the pristine zigzag nanotubes. Using the magnitude of the bandgap modulation, the order of suitability of the different nanomaterials was established as follows: PBN60 (0.19%) < PC70 (1.39%) < PC60 (1.77%) < PBNNT (27.64%) < PCNT (65.29%) < PBN70 (134.12%). Since the desired criterion for the design of an electronic device is increased conductivity after adsorption due to the resulting low power consumption, PC60 was found to be most suitable because of its power consumption as it had the largest decrease of 1.77% of the bandgap.     

Analysis of Free and Total Glycerol in Biodiesel Using an Electrochemical Assay Based on a Two‐Enzyme Oxygen‐Electrode System

In this work, an electroenzymatic methodology based on two coupled enzymatic activities (glycerokinase and glycerol‐3‐phosphate oxidase) was developed using an oxygen Clark‐type electrode for the determination of free and total glycerol in biodiesel samples. The enzymatic conversion of glycerol consumes oxygen, which is measured amperometrically in a Clark‐type electrode and correlated with the concentration of glycerol in the sample. The electroenzymatic method proposed showed a good linear correlation coefficient (R=0.9990) with a linear response in the concentration range of 6.25×10^?5 to 6.25×10^?4% (w/v) and limits of detection and quantification at 1.0×10^?5% and 3.0×10^?5% (w/v), respectively. Good correlations were found between the results obtained in this work and those by the gas chromatography technique (R=0.9994). The proposed method was shown to be promising for the analysis of glycerol in biodiesel samples, with a simple and inexpensive methodology compared with the gas chromatography technique.     

容量法与失重法测定碳钢腐蚀速率的比较研究

静态失重法是一种测定酸化腐蚀速率的基本方法,但存在耗时长、操作繁琐等缺点。为了弥补静态失重法的不足,研究了容量法测定腐蚀速率的可行性,分析了两种方法所测结果存在差异的原因。结果表明,容量法与失重法测得的腐蚀速率有较高的一致性,其相对平均偏差未超过4%。最后根据接触角测试结果,分析了产生这种偏差的原因。     

A New Approach how to Define the Coefficient of Electroactivity of Adenine and Its Twelve Derivatives Using Flow Injection Analysis with Amperometric Detection

We studied the electrochemical behaviour of adenine derivates (adenosine, 2‐aminopurine, 2,6‐diaminopurine, 6‐benzyl‐aminopurine, adenosine monophosphate, cyclic adenosine monophosphate, nicotinamide adenine dinucleotide, adenosine triphosphate, S‐adenosyl‐L ‐methionine, and synthetic derivatives AD‐3, AD‐6 and AD‐9) using flow injection analysis with electrochemical detection using a glassy carbon electrode. The influences of pH, flow rate and potential on the signal height of the studied derivates were tested. The optimal pH was 3, the flow rate of the mobile phase 0.75 mL min^?1 and the potential 1100 mV. Further, we attempted to characterize each of the studied derivatives by mathematical equations and classic analytical parameters. The lowest detection limit was estimated for adenine as 0.9 nM and 2‐aminopurine as 0.5 nM.     

Comparative Study on Electroanalysis of Fenthion Using Silver Amalgam Film Electrode and Glassy Carbon Electrode Modified with Reduced Graphene Oxide

Oxidation and reduction processes of the insecticide fenthion was comparatively investigated at a reduced graphene oxide modified glassy carbon electrode (RGO‐GCE) and a cyclic renewable silver amalgam film electrode (Hg(Ag)FE) using square wave stripping voltammetry (SWSV). The influence of pH and SW parameters was investigated. The linear concentration ranges were found to be 1 × 10⁻⁶ – 2 × 10⁻⁵ and 1 × 10⁻⁷ – 2 × 10⁻⁵ mol L⁻¹ for Hg(Ag)FE and RGO‐GCE, respectively. The detection and quantification limits were calculated as 1.3 × 10⁻⁷ and 4.5 × 10⁻⁷ mol L⁻¹ for Hg(Ag)FE and 7.6 × 10⁻⁹ and 2.5 × 10⁻⁸ mol L⁻¹ for RGO‐GCE. Both of the developed electroanalytical methods offer rapid and simple detection of fenthion and were used on spiked tap and river water and apple juice samples. Scanning electron microscopy was used for RGO‐GCE surface characterization.