Determination of zidovudine using anion exchange chromatography with integrated pulsed amperometric detection

A rapid and practical method for direct detection of zidovudine in high performance anion exchange chromatography(HPAEC) has been developed with integrated pulsed amperometric detection(IPAD).Dionex AS 18(250 mm×2 mm) and AG 18 (50 mm x 2 mm) columns and 11 mmol/L NaOH solution were used for separation.Multi-step potential waveform parameters were optimized to maximize the signal-to-noise ratio(S/N).Utilizing an optimized waveform,the repeatability(intra-day) precision and intermediate(inter-day) precision are obtained with relative standard deviation(RSD) of 1.88,2.27,respectively.The limit of quantification(LOQ) and limit of detection(LOD) were found to be 9.70,3.0 ng/mL,respectively,with correlation coefficients of 0.9992 over concentration range 0.01-10μg/mL.The present method was successfully applied to the determination of zidovudine in human plasma.The recoveries of plasma sample spiked by 0.7μg/mL,2.7μg/mL obtained were 95.3-101.5%, with relative standard deviation(RSD) of 2.54%,2.21%,respectively.     

Sample preparation and current applications of liquid chromatography for the determination of non-structural carbohydrates in plants

This article summarizes the current methods of determination of non-structural carbohydrates (NSCs) in plant samples based on liquid chromatography (LC). NSCs comprise several types of carbohydrates: sugar alcohols (e.g., sorbitol), monosaccharides (e.g., glucose and fructose), disaccharides (e.g., sucrose), oligosaccharides (e.g., raffinose) and polysaccharides [e.g., starch and polyfructans (e.g., inulin)]. NSCs are important in plant metabolism and have to be strictly distinguished from all sorts of structural carbohydrates (e.g., polysaccharide cellulose) that make up the backbone of the plants. Consequently, preservation of structural carbohydrates is a crucial step during sample preparation for NSC determination and is therefore addressed.Sugar alcohols, monosaccharides, disaccharides and those oligosaccharides that are easily soluble in polar solvents can be analyzed directly by high-performance LC. They are also referred to as free carbohydrates (FCs).However, polysaccharides are generally submitted to hydrolyzation into monomers prior to their quantitative analysis. This can be done either chemically, using acids, or enzymatically - both methods are discussed. For identification and quantification of the NSCs after LC separation, the following detectors are used: pulsed amperometry, refractive index, evaporate light scattering and finally, mass spectrometry.     

Reconstruction of Aperture Functions during Full Fusion in Vesicular Exocytosis of Neurotransmitters

Individual vesicular exocytosis of adrenaline by dense core vesicles in chromaffin cells is considered here as a paradigm of many situations encountered in biology, nanosciences and drug delivery in which a spherical container releases in the external environment through gradual uncovering of its surface. A procedure for extracting the aperture (opening) function of a biological vesicle fusing with a cell membrane from the released molecular flux of neurotransmitter as monitored by amperometry has been devised based on semi‐analytical expressions derived in a former work [C. Amatore, A. I. Oleinick, I. Svir, ChemPhysChem 2009 , 10, DOI: 10.1002/cphc.200900646]. This precise analysis shows that in the absence of direct information about the radius of the vesicle or about the concentration of the adrenaline cation stored by the vesicle matrix, current spikes do not contain enough information to determine the maximum aperture angle. Yet, a statistical analysis establishes that this maximum aperture angle is most probably less than a few tens of degrees, which suggests that full fusion is a very improbable event.     

甲氧苄啶修饰玻碳电极安培法对过氧化氢的测定

在0.1 mol·L~(-1) KNO_3底液中,研究了甲氧苄啶在玻碳电极上的电化学性质,发现在0.140、0.177 V处出现1对可逆的氧化还原峰.进一步用电化学沉积的方法将甲氧苄啶修饰在玻碳电极上,考察了各种实验条件对修饰电极性能的影响,并通过电子扫描显微镜和电化学阻抗谱对修饰电极的表面性质进行了表征,所制得的修饰电极对过氧化氢的还原有很好的催化作用.在-0.3 V的工作电位下,用计时安培法对过氧化氢进行了测定,过氧化氢的浓度在1.96×10~(-5) ～1.10×10~(-3) mol·L~(-1)范围内与响应电流呈线性关系,检出限为4.0 μmol·L~(-1).该修饰电极制作简单、使用寿命长,实际试样的回收率为97% ～104%.     

Polyethylenimine Functionalized Multi‐walled Carbon Nanotubes for Electrochemical Detection of Chromium(VI)

Multi‐walled carbon nanotubes (MWCNTs) functionalized with polyethylenimine (PEI) were synthesized and characterized by dispersibility, field‐emission scanning electron microscope (FE‐SEM), FT‐IR and thermogravimetric Analyzer (TGA). The glassy carbon electrodes modified by MWCNT‐PEI composite were used for sensitive and selective detection of chromium (VI). A linear response was obtained over a wide range of Cr(VI) concentrations (0.002–20 µmol L^?1) with the detection limit of 0.0006 µmol L^?1 (S/N=3). The proposed electrodes were used successfully for Cr(VI) detection in three real water samples.     

PEDOT/Superoxide Dismutase Electrode Surface Modification for Superoxide Bioelectrochemical Sensing

An amperometric biosensor for the sensitive detection of superoxide was designed utilizing a drop‐coating approach for immobilizing the superoxide dismutase enzyme on Pt electrode modified with a thin layer of poly (3,4‐ethylenedioxythiophene) (PEDOT). The layer electrodeposited on Pt was characterized by cyclic voltammetry and atomic force microscopy (AFM). Then, drop‐coating procedure was chosen for the immobilization of superoxide dismutase (SOD), which was incorporated at the electrode surface using a solution containing SOD, glutaraldehyde and bovine serum albumin (optimized composition: SOD 0.1 % – BSA 2 % – GA 2.5 %.) This simple procedure allows forming a reproducible enzymatic biocomposite layer that allows optimal sensitivity and limit of detection for superoxide sensing. The synergistic effect integrates an effective conductivity and permselectivity attributed to the PEDOT layer, as well as the specificity and selectivity of SOD for the detection of superoxide. A high sensitivity (0.82±0.01 μA/μM) and a low detection limit of 11 nM were obtained, as well as good selectivity against main interfering biological compounds such as uric acid and ascorbic acid. Our results suggest that the biosensor could be used for the detection and quantification of in vitro and in vivo.     

Fast and Simple Electrochemical Analysis Kit for Quality Control of Narrow Therapeutic Index Drugs

The use of multiple‐pulse amperometry (MPA) for the determination of narrow therapeutic index (NTI) drugs using batch injection analysis (BIA) with carbon screen‐printed electrodes (SPE) is proposed, seeking to develop a practical and low‐cost analysis kit for application in routine quality control of these drugs. The electrochemical behaviors of aminophylline, carbamazepine, clindamycin, colchicine, minoxidil, prazosin, procainamide, theophylline, warfarin and verapamil were evaluated in different electrolytes, but just one, the 0.1 mol L⁻¹ phosphate buffer, pH 7.0, was chosen for determination of all the analytes. The amperometric detection was optimized as a function of the best oxidation potential for carbon SPE for each analyte, which was in a range from 0.7 to 1.1 V. The injection conditions were determined as a function of the velocity and the volume injected by the BIA system, which were 92.5 μL s⁻¹ and 100 μL, respectively. Under these conditions, a good repeatability (RSD<3 %), high analytical frequency (>215 determinations per hour), large linear ranges and low LOD (<0.42 μmol L⁻¹) for all the NTI drugs were obtained. Furthermore, the proposed method provided an easy qualitative analysis of the investigated analytes using MPA detection. The addition‐recovery studies in pharmaceutical samples containing NTI drugs and the comparison with official methods showed that the proposed analysis Kit is a very fast, simple and efficient alternative for quantification of these analytes.     

Voltammetric Detection of the Herbicide Metamitron at a Bismuth Film Electrode in Nondeaerated Solution

In this work, we present a novel application of bismuth film electrodes (BiFE) for the direct analysis of the herbicide metamitron (4‐amino‐3‐methyl‐6‐phenyl‐1,2,4‐triazin‐5one) in nondeaerated solutions by square‐wave voltammetry (SWV) and differential pulse amperometry. Bismuth films were plated ex‐situ onto carbon paste electrodes (CPE) by 240 s deposition at ?0.600 V from a 0.10 M acetate buffer (pH 4.5) containing 0.50 mM bismuth nitrate. Metamitron SWV analytical signals were registered in 0.10 M acetate buffer (pH 4.5) solutions, where the herbicide reduction takes place at ?0.675 V. The metamitron signals obtained with BiFE have the double sensitivity and a 50 mV positive potential shift when compared to those obtained with plain CPE. Under these conditions, the dynamic linear range of concentrations is comprised between 10 and 200 μM and the detection limit is 2 μM.     

Electrochemical reduction and flow detection of iodate on (Bu<Subscript>4</Subscript>N)<Subscript>2</Subscript>Mo<Subscript>6</Subscript>O<Subscript>19</Subscript> self-assembled monolayer

A stable monolayer of the inorganic–organic hybrid polyoxometalate (Bu₄N)₂Mo₆O₁₉, denoted as Mo₆O₁₉, was formed on a sodium-3-mercapto-1-propanesulfonate (MPPS)-covered gold electrode surface, interlaced with an anionic poly(dimethyldiallylammonium chloride) (PDDA) binding layer based on the electrostatic self-assembled (ESA) technique. Electrochemical characterization of the Mo₆O₁₉ self-assembled thin films on the solid surface by cyclic voltammetry and AC impedance spectroscopy revealed a stable and sensitive electrocatalytic response to the reduction of iodate. Iodate was determined amperometrically through a flow injection cell at the modified electrode in the concentration range of 1.0×10^–6 to 1.0×10^–1 M with a detection limit of 8×10^–8 M (signal-to-noise ratio = 3). Performance was improved to meet practical needs compared with previously reported analogues.