Voltammetric Determination of Pb,Cu and Hg in Biodiesel Using Gold Screen‐printed Electrode: Comparison of Batch‐injection Analysis with Conventional Electrochemical Systems

This article compares the use of batch‐injection analysis (BIA) with a conventional batch system for the anodic stripping voltammetric (ASV) determination of Pb, Cu and Hg in biodiesel using screen‐printed gold electrode (SPGE). The optimized BIA conditions were 200 µL of injection volume of the digested samples at 5 µL s^?1 directly on the working electrode of the SPGE immersed in 0.1 mol L^?1 HCl solution. Therefore, BIA‐ASV presented the advantages of low sample consumption, which extended the SPGE lifetime to a whole working day of analyses, and potential for on‐site analysis using battery‐powered micropipettes and potentiostats. Although presenting lower sensitivity than conventional systems, the BIA‐ASV presented detection limit values of 1.0, 0.5 and 0.7 µg L^?1, respectively for Pb, Cu and Hg, a linear range between 20 and 280 µg L^?1, and adequate recovery values (90–110 %) for spiked biodiesel samples.     

Electrochemical Oxidation of Astaxanthin on Glassy‐carbon Electrode and its Amperometric Determination Using Batch Injection Analysis (BIA)

This work presents the electrochemical oxidation of the antioxidant astaxanthin on a glassy‐carbon electrode (GCE) and its amperometric determination in salmon samples using a batch‐injection analysis (BIA) system. The proposed BIA method consisted of 80‐µL a fast microliter injection of sample at 193 µL s^?1 on the GCE immersed in the electrolyte, a mixture of acetone, dichloromethane, and water (80 : 10 : 10 v/v), containing 0.1 mol L^?1 HClO₄. Advantages include high precision (RSD of 2.4 %), sample throughput of 240 h^?1, and low detection limit (0.3 µmol L^?1 that corresponds to 0.1 µg g^?1) for the analysis of acetone extracts of salmon samples. Recovery values between 83 and 97 % attested the accuracy of the method.     

On‐Site Determination of Carbendazim,Cathecol and Hydroquinone in Tap Water Using a Homemade Batch Injection Analysis Cell for Screen Printed Electrodes

In this work, we present a simple homemade batch‐injection analysis cell for screen‐printed electrodes (BIA‐SPE). The potential of the proposed system for on‐site analysis was demonstrated by the determination of carbendazim, catechol, and hydroquinone in tap water. The system provided reduced injection volume (30 µL), high analytical frequency (≈200 h^?1) and low detection limits (nanomolar level). Moreover, the BIA‐SPE cell presented better stability (RSD≈0.4 %) than a conventional flow injection cell for SPE (RSD≈5.0 %) in organic media. The proposed homemade BIA‐SPE cell is very simple, inexpensive and can be easily constructed in any laboratory.     

Flow‐Injection Pulsed‐Amperometric Determination of Free Glycerol in Biodiesel at a Gold Electrode

This work reports the highly‐sensitive amperometric determination of free glycerol in biodiesel at a gold electrode adapted in a flow‐injection analysis (FIA) cell. The amperometric method involved the continuous application of three sequential pulses to the working electrode (+250 mV, +700 mV, and ?200 mV, for 100 ms each). This sequence of potential pulses eliminated electrode passivation and dramatically increased the analytical signal. The proposed FIA‐amperometric method presented low relative standard deviation between injections (1.5 %, n=15), high analytical frequency (85 h^?1), satisfactory recovery values (93–118 %) for spiked samples, wide linear range (from 1 to 300 µmol L^?1), and low detection limit (0.5 µmol L^?1).     

Amperometric Folic Acid Quantification Using a Supramolecular Tetraruthenated Nickel Porphyrin µ‐Peroxo‐Bridged Matrix Modified Electrode Associated to Batch Injection Analysis

A supramolecular Nickel (II) porphyrin complex containing four pyridyl‐bis(2,2′‐bipyridyl)chloro ruthenium meso substituents was submitted to successive voltammetric cycles in high alkaline media to produce a supramolecular matrix with Nickel centers linked by µ‐peroxo bridges, producing a highly stable thin film able to act as redox mediator for electrocatalytic oxidation of folic acid. The characterization of electrode surface material was performed by Scanning Electron Microscopy and Electrochemical Impedance Spectroscopy. The modified electrode was inserted into a batch injection electrochemical cell used for the rapid and precise quantification of folic acid in pharmaceutical products. The favorable hydrodynamic conditions provided by amperometry‐BIA association allowed a very high throughput with good linear range (1 to 200 µmol L^?1) and low detection limit (7.37×10^?7 mol L^?1). The electrochemical method was applied to the quantification of folic acid in different tablet samples. The results were comparable with values indicated by the manufacturer and those found using high HPLC according to the Brazilian Pharmacopoeia; commercial samples were submitted to a procedure in order to remove lactose of tablets, since carbohydrates act as interfering species. This procedure together with the electrochemical method showed to be simple, rapid, efficient and an appropriate alternative for quantifying this compound in real samples.     

Developing a novel packed in‐tube solid‐phase extraction method for determination ∆9‐tetrahydrocannabinol in biological samples and cannabis leaves

A novel plate‐like nano‐sorbent based on copper/cobalt/chromium layered double hydroxide was synthesized by a simple coprecipitation method. The synthesized nanoparticels were introduced into a stainless steel cartridge using a dry packing method. Then, the packed cartridge was introduced as a novel on‐line “packed in‐tube” configuration and followed by high performance liquid chromatography for the determination of trace amounts of ^?9‐tetrahydrocannabinol from biological samples and cannabis leaves. The as‐prepared sorbent exhibited long lifetime, good chemical stability, and high anion‐exchange capacity. Several important factors affecting the extraction efficiency, such as extraction and desorption times, pH of the sample solution and flow rates of the sample and eluent solutions, were investigated and optimized. Under optimized conditions, this method showed good linearity for ^?9‐tetrahydrocannabinol in the ranges of 0.09–500, 0.3–500, and 0.4–500 µg/L with coefficients of determination of 0.9999, 0.9991, and 0.9994 in water, serum and plasma samples, respectively. The inter‐ and intra‐assay precisions (n = 3) were respectively in the ranges of 1.8–4.6% and 1.9–4.0% at three concentration levels of 10, 50, and 100 µg/L. The limits of detection were also in the range of 0.02–0.1 µg/L.     

Voltammetric Determination of 4‐Nitrophenol and 5‐Nitrobenzimidazole Using Different Types of Silver Solid Amalgam Electrodes – A Comparative Study

The voltammetric behavior of two genotoxic nitro compounds (4‐nitrophenol and 5‐nitrobenzimidazole) has been investigated using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at a polished silver solid amalgam electrode (p‐AgSAE), a mercury meniscus modified silver solid amalgam electrode (m‐AgSAE), and a mercury film modified silver solid amalgam electrode (MF‐AgSAE). The optimum conditions have been evaluated for their determination in Britton‐Robinson buffer solutions. The limit of quantification (L_Q) for 5‐nitrobenzimidazole at p‐AgSAE was 0.77 µmol L^?1 (DCV) and 0.47 µmol L^?1 (DPV), at m‐AgSAE it was 0.32 µmol L^?1 (DCV) and 0.16 µmol L^?1 (DPV), and at MF‐AgSAE it was 0.97 µmol L^?1 (DCV) and 0.70 µmol L^?1 (DPV). For 4‐nitrophenol at p‐AgSAE, L_Q was 0.37 µmol L^?1 (DCV) and 0.32 µmol L^?1 (DPV), at m‐AgSAE it was 0.14 µmol L^?1 (DCV) and 0.1 µmol L^?1 (DPV), and at MF‐AgSAE, it was 0.87 µmol L^?1 (DCV) and 0.37 µmol L^?1 (DPV). Thorough comparative studies have shown that m‐AgSAE is the best sensor for voltammetric determination of the two model genotoxic compounds because it gives the lowest L_Q, is easier to prepare, and its surface can be easily renewed both chemically (by new amalgamation) and/or electrochemically (by imposition of cleaning pulses). The practical applicability of the newly developed methods was verified on model samples of drinking water.     

Batch‐injection Amperometric Analysis on Screen‐printed Electrodes: Analytical System for High‐throughput Determination of Pharmaceutical Molecules

This work presents a single analytical system able to perform high‐throughput determinations of different pharmaceutical molecules on screen‐printed electrodes (SPEs) assembled on a batch‐injection analysis (BIA) cell. Two types of SPEs, both containing a carbon conductive ink as working electrode, were selected for the determination of levamisole (LVM) in aqueous and sodium levothyroxine (NaLVT) in hydroethanolic media. The main analytical characteristics of the proposed system for both examples are high precision (RSD <3.8 %, n=10), low detection limits (submicromolar range), and high sample‐throughput (>150 h^?1) using a single SPE, demonstrating the extended lifetime of such sensors, which are adequate for routine pharmaceutical analysis. The proposed analytical system requires battery‐powered portable devices, including potentiostat and reader, electronic micropipette, BIA cell and SPEs, and can be applied for a wide range of pharmaceutical molecules. In case of analyte adsorption on electrode surface, fast electrode cleaning can be supplied by external stirring easily adapted to the cell, which is demonstrated in this work for NaLVT determination.     

A portable lab‐on‐a‐chip instrument based on MCE with dual top–bottom capacitive coupled contactless conductivity detector in replaceable cell cartridge

A new design for a compact portable lab‐on‐a‐chip instrument based on MCE and dual capacitively coupled contactless conductivity detection (dC⁴D) is described. The instrument is battery powered with total dimension of 14 × 25 × 8 cm³ (w × l × h), and weighs 1.2 kg. The device consists of a front electrophoresis compartment which has the chip holder and the chip, the associated high‐voltage electrodes for electrophoresis injection and separation and the detector. The detection cell is integrated into the device housing with an exchangeable plug‐and‐play cartridge format. The design of the dC⁴D cell has been optimized for maximum performance. The cartridge includes the top–bottom excitation and pick up electrodes incorporated into the cell and connected to push‐pull self‐latching pins that are insulated with plastic. The metal frame of the cartridge is grounded completely to eliminate electronic interferences. The cartridge is designed to clamp a thin fluidic chip at the detection point. The cartridges are replaceable whereby different cartridges have different detection electrode configurations to employ according to the sensitivity or resolution needed in the specific analytical application. The second compartment consists of all the electronics, data acquisition card, high‐voltage modules of up to ±5 kV both polarity, and batteries for 10 h of operation. The improved detector performance is illustrated by the electrophoresis analysis of six cations (NH₄⁺, K⁺, Ca²⁺, Na⁺, Mg²⁺, Li⁺) with a detection limit of approximately 5 μM and the analysis of the anions (Br^?, Cl^?, NO₂^?, NO₃^?, SO₄^2?, F^?) with a detection limit of about 3 μM. Analytical capabilities of the instrument for food and medical applications were evaluated by simultaneous detection of organic and inorganic acids in fruit juice and inorganic cations and anions in rabbit blood samples and human urine samples are also demonstrated.     

Batch‐injection versus Flow‐injection Analysis Using Screen‐printed Electrodes: Determination of Ciprofloxacin in Pharmaceutical Formulations

This article highlights the potential use of multi‐walled carbon‐nanotube modified screen‐printed electrodes (SPEs) for the amperometric sensing of ciprofloxacin and compares the association of batch‐injection analysis (BIA) and flow‐injection analysis (FIA) with amperometric detection. Both analytical systems provided precise (RSD<5 %) and sensitive determination of ciprofloxacin (LOD<0.1 μmol L^?1) within wide linear range (up to 200 μmol L^?1). Accuracy of both methods was attested by recovery values (93–107 %) and comparison with capillary electrophoresis. The BIA system is completely portable (especially due to association with SPEs) and provided faster analyses (130 h^?1) and more sensitive detection than the FIA system due to the higher flow rates of injection.     

HPLC法拆分(-)-2(S)-苄基-4-酮-4-(顺式-全氢化异吲哚-2-基)丁酸钙对映体

目的：建立刺激胰岛素分泌的新型降糖药物(-)-2 (S)-苄基-4-酮-4-(顺式-全氢化异吲哚-2-基)丁酸钙对映体的HPLC拆分方法。方法：采用Sumichiral OA-3300手性柱(250 × 4.6 mm I.D., 5 μm), 柱温35℃,以0.05 mol·L-1醋酸铵的甲醇溶液为流动相,检测波长为210 nm。结果：本品两对映体在22分钟内实现良好分离,分离度达3以上,S－异构体分别在0.028 ~ 5.6 μg mL-1和0.03 ~ 6.0 μg mL-1范围内线性关系良好,回归方程分别为：Y=1.32×103x-2.54 (r=0.9997)和Y=1.15×103x-1.78 (r=0.9998),最低检测限分别为0.15 ng和0.10 ng,方法精密度RSD低于1.0% (n=5)。结论：建立的对映体分离方法可用于本品光学异构体的质量控制。     

Ion chromatography–hydride generation‐atomic fluorescence spectrometry speciation of tellurium

The speciation of tellurium was carried out using atomic fluorescence spectrometry as an element‐specific detector in hybridization with liquid chromatography and hydride generation. Good resolution could be obtained by anion‐exchange chromatography with complexing agents, using a mobile phase with 8 mM EDTA and 2 mM potassium hydrogenphthalate. Analysis time was less than 6 min. Calibration graphs were linear between 2 and 100 µg l^?1. Detection limits were 0.6 µg l^?1 and 0.7 µg l^?1 for tellurium(VI) and tellurium(IV) respectively. The method was applied to the speciation of tellurium in drinking water and wastewater samples from different metallurgical industries. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthetic and antimicrobial studies on new gold(I) complexes of imidazolidin‐2‐ylidenes

Six new 1,3‐diorganylimidazolidin‐2‐ylidene (NHC) gold(I) complexes of the type [Au(NHC)₂]⁺ (1–6), were synthesized by reacting [AuCl(PPh)₃] with 1,3‐dimesitylimidazolidin‐2‐ylidene or bis(1,3‐dialkylimidazolidin‐2‐ylidene). The complexes 1–6 were fully characterized by elemental analyses and spectroscopic data. The placement of mesityl or para‐substituted benzyl groups on the nitrogen atoms of the ring of the complexes leads to the particularly active antibacterial agents evaluated in this work. It is worth noting that the p‐methoxybenzyl derivative (2) inhibited the growth of Pseudomona aeruginosa, Staphylococcus epidermidis, Staphylococcus aureus and Enterococcus faecalis with minimum inhibitory concentration (MIC) values of 3.12 µg ml^?1, 6.25 µg ml^?1, 3.12 µg ml^?1 and 3.12 µg ml^?1 respectively. In contrast, the analogous p‐dimethylaminobenzyl derivative (3) is effective only against Escherichia coli (MIC = 3.12 µg ml^?1). Copyright © 2004 John Wiley & Sons, Ltd.     

Optimization and validation of an ion‐pair RP‐HPLC‐UV method for the determination of total free iodine in rabbit plasma: application to a pharmacokinetic study

An ion‐pair reverse‐phase high performance liquid chromatographic method with UV–vis detection has been developed for the determination of total free iodine in rabbit plasma after vaginal administration of povidone–iodine (PVP‐I). Sample preparation was done by protein precipitation with acetonitrile in 96‐well format and aspirin was used as the internal standard. The 100 µL sodium thiosulfate solution (5 g L^?1) was added to 100 µL plasma sample before protein precipitation, to convert the total free iodine in plasma to iodide (I^?). Separation was performed on a C₁₈ column (200 × 4.6 mm i.d., 5 µm). The mobile phase consisting of a mixture of water phase (containing 10 mmol L^?1 18‐crown‐6 ether, 5 mmol L^?1 octylamine and 5 mmol L^?1 sodium dihydrogen phosphate, pH adjusted to 6.0 with phosphoric acid) and acetonitrile in the ratio 70:30 (v/v) was delivered isocraticly at a flow rate of 1.0 mL min^?1. The method was sensitive with a lower limit of quantification of 0.005 µg mL^?1, with good linearity (r² > 0.9990) over the linear range of 0.005–2 µg mL^?1. All the validation data, such as linearity, accuracy and precision, were within the required limits. The method was successfully applied to study the pharmacokinetic of PVP–I in rabbits after vaginal administration. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of Sulfite in Hair Waving Products Using Oxygen‐Incorporated Gold‐Modified Screen‐Printed Electrodes

An electrodeposition oxygen‐incorporated gold‐modified screen‐printed carbon electrode (AuOSPE) was fabricated to determine the sulfite content in hair waving products. The AuOSPE showed an electrocatalytic current for sulfite at +0.4 V (vs. Ag/AgCl). Compared with a gold screen‐printed electrode (AuSPE), the AuOSPE showed a higher electrocatalytic current. The increase in the electrocatalytic current was ascribed to the increase of the oxygen incorporated with gold atom on AuOSPE. The AuOSPE coupled with a flow injection analysis (FIA) system showed excellent oxidation current for sulfite in a 0.1 mol L^?1 phosphate buffer solution (PBS), pH 6.0. The linear working range for determining the sulfite content was 0.05 to 1200 mg L^?1 (0.625 µmol L^?1 to 15.00 mmol L^?1) with a calculated detection limit of 0.03 mg L^?1 (0.375 µmol L^?1) (DL, S/N=3). Relative standard deviations (RSD) of 3.03 %, 2.30 % and 4.26 % were calculated for consecutive injections (n=12) of 20, 300 and 900 mg L^?1 sulfite, respectively. The amount of sulfite in two hair waving products was determined by the proposed method and a standard iodometric method. The recoveries ranged from 96.18 % to 105.61 %. The AuOSPE showed high sensitivity, selectivity, stability and reproducibility for sulfite.     

N‐(3,4‐Dihydroxyphenethyl)‐3,5‐dinitrobenzamide‐Modified Multiwall Carbon Nanotubes Paste Electrode as a Novel Sensor for Simultaneous Determination of Penicillamine,Uric acid,and Tryptophan

N‐(3,4‐dihydroxyphenethyl)‐3,5‐dinitrobenzamide modified multiwall carbon nanotubes paste electrode was used as a voltammetric sensor for oxidation of penicillamine (PA), uric acid (UA) and tryptophan (TP). In a mixture of PA, UA and TP, those voltammograms were well separated from each other with potential differences of 300, 610, and 310 mV, respectively. The peak currents were linearly dependent on PA, UA and TP concentrations in the range of 0.05–300, 5–420, and 1.0–400 µmol L^?1, with detection limits of 0.021, 2.0, and 0.82 µmol L^?1, respectively. The modified electrode was used for the determination of those compounds in real samples.     

Fast Determination of Ciprofloxacin by Batch Injection Analysis with Amperometric Detection and Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

We report fast, precise, selective, and sensitive electroanalytical methods for the determination of ciprofloxacin in milk and pharmaceutical samples by batch‐injection analysis with amperometric detection (BIA‐AMP) and by capillary electrophoresis with capacitively‐coupled contactless conductivity detection (CE‐C⁴D). Both methods required simple sample preparation protocols before analysis (milk samples were just diluted and tablets powdered and dissolved in electrolyte/water). The analytical features of BIA‐AMP and CE‐C⁴D methods include, respectively, low relative standard deviation values for repetitive measurements (2.8 % and 1.7 %, n=10), low detection limits (0.3 and 5.0 µmol L^?1), elevated analytical frequency (80 and 120 h^?1) and satisfactory accuracy (based on comparative determinations by HPLC and recovery values for spiked samples).     

Quantification issues of trace metals analysis on silicon oxide and nitride films by using VPD‐ICP‐MS and VPD‐GF‐AAS

Vapor phase decomposition (VPD) is a pretreatment technique for collecting trace metal contaminants on the surface of a Si wafer. Such trace metals can be identified and quantified by inductively coupled plasma mass spectrometry (ICP‐MS) or graphite furnace atomic absorption spectroscopy (GF‐AAS). However, the analytical results can be influenced by the Si‐matrix in the VPD samples. This article discusses the approaches to eliminate the interference caused by Si‐matrix. When the thickness of oxide film on wafer surface is less than 100 Å, the quantification results of ICP‐MS analysis will not be affected by Si‐matrix in the VPD samples. Except this, the Si‐matrix must be removed before analysis. An improved heating pretreatment approach has been adopted successfully to eliminate the Si‐matrix. For GF‐AAS analysis, the Si‐matrix will influence the sodium and aluminum analyses. Adding HNO₃ to the graphite furnace tubing after sample injection could also eliminate the interference caused by the Si‐matrix. The method detection limits (MDLs) of VPD‐GF‐AAS and VPD‐ICP‐MS range from 0.04 to 0.55 × 10¹⁰ atoms cm^?2 and 0.05 to 1.73 × 10⁹ atoms cm^?2, respectively. Copyright © 2008 John Wiley & Sons, Ltd.     

Label‐Free Amperometric Detection of Albumin with an Oil/Water‐type Flow Cell for Urine Protein Analysis

The 1,2‐dichloroethane (DCE)/water interface, with an anionic surfactant, dinonylnaphthalenesulfonate (DNNS^?), being present in DCE, was utilized for label‐free detection of albumin. An oil/water‐type flow cell was prepared using a porous PTFE tube and dipping the tube in the DCE solution containing DNNS^?. This flow cell provided a well‐defined current response linear to the albumin concentration up to 10 µM with a detection limit of 1.2 µM. The current response is due to the interfacial adsorption of albumin molecules depending on the Galvani potential difference. Possible interference from creatinine in the urine could be avoided by a conventional dialysis treatment.     

Analytical Applications of 2,6‐Diacetylpyridine‐bis‐4‐phenyl‐3‐thiosemicarbazone (2,6‐DAPBPTSC): Determination of Cd(II) in Foods and Water Samples

To the determination of trace amount of Cd(II) present in food and water samples, a selective and extractive spectrophotometric method were developed with 2,6‐diacetylpyridine‐bis‐4‐phenyl‐3‐thiosemicarbazone as a complexing agent. The yellowish orange colored metal complex, Cd(II)‐2,6‐DAPBPTSC with 1:1 (M:L) composition was extracted in to cyclohexanol at pH 9.5 and was shows maximum absorbance at λ_max 390 nm. This method obeys Beer's law in the range of 1.12‐11.25 ppm with 0.972 correlation coefficient of Cd(II)‐2,6‐DAPBPTSC complex, which is indicates linearity between the two variables. The molar absorptivity and sandell's sensitivity were found to be 6.088 × 10⁴ L mol^?1 cm^?1 and 0.0018 μg cm^?2, respectively. The instability constant calculated from Asmus' method (1.447 × 10^?4)at room temperature. The precision and accuracy of the method were checked by relative standard deviation (n = 5), 0.929 and its detection limit, 0.0060 μg mL^?1. The interfering effects of various cations and anions were also studied. The proposed method was successfully applied to the determination of Cd(II) in foods and water samples, and was evaluated its performance in terms of Student ‘t’ test and Variance ‘f’ test, which indicates the significance of present method. The inter comparison of the experimental values, using atomic absorption spectrometer (AAS), was also repoted.