Iodide analysis by ion chromatography on a new stationary phase of polystyrene-divinylbenzene agglomerated with polymerized-epichlorohydrin-dimethylamine

A new stationary phase for iodide ion analysis has been developed. The cationic polymerepichlorohydrin-dimethylamine(PEPI-DMA) was served as modifier in synthesizing polyelectrolyte sorbents and the macroporous polystyrene-divinylbenzene(PS-DVB) resin was used as support. The positively charged polymer(PEPI-DMA) was electrostatically bonded to a negatively charged particle(PS-DVB sulfonated). The new stationary phase was characterized by scanning electron microscopy(SEM), Fourier transform infrared(FTIR), elemental analysis, chemical adsorption and desorption measurements. The chromatographic evaluation of the new stationary phase was performed using various anions with a conductivity detector. The new stationary phase was also applied to the determination of iodide directly with a DC amperometric detector using a platinum working electrode and an Ag/Ag Cl reference electrode. The chromatographic conditions were optimized and the eluent solution contained 5 mmol/L HNO3 and 15 mmol/L Na NO3 at a flow rate of 1.0 m L/min and column temperature of 30 8C. The applied voltage of the DC amperometric detector was 0.9 V. Under the optimum conditions, the linear range of the method was 0.2–50 mg/L for iodide ion with a correlation coefficient of 0.9990. The detection limit was 0.05 mg/L(calculated at S/N = 3) and the relative standard deviations(RSD, n = 6) were all less than 1% for retention time, peak area and peak height. This method was also utilized for the determination of iodide ions in samples of povidone iodine solution and kelp samples with satisfactory results.     

A New Dual-electrode and Multi-channel Electrochemical Detection System for Capillary Electrophoresis

A new type of dual-electrode and multi-channel electrochemical detection technology for capillary electrophoresis is described in this paper.Two detectors(the amperometric detector and the conductometric detector) or two conductometric detectors are connected to the same capillary electrophoresis system.The whole system possesses the advantages of the two electrochemical detectors including sparing time,improving the analytical speed and expanding the sample range.The working electrode and detector cell are handled easily.The system was applied to sample detection with satisfactory results.     

Multianalyte Biosensor for Simultaneous Determination of Glucose and Galactose Based on Micromachined Chamber-type Electrodes

An amperometric multianalyte biosensor for the simultaneous determination of glucose and galactose was developed based on chamber-type electrodes, which were fabricated by micromachining technology. The dual cham-ber-type enzyme electrode with glucose and galactose sensor elements was integrated onto one microchip. The experimental parameters of this biosensor were optimized. The biosensor exhibited a linearity of up to 4.0 mol/L for glucose and 4.5 mol/L for galactose, and the response time was about 30 s for glucose and 40 s for galactose. No cross-talking behavior was investigated in the course of simultaneous measurement of the two analytes. Interference from electroactive species, such as ascorbic acid and uric acid, was minimized due to the permselectivity of Nation film. In addition, the biosensor displayed a storage stability of longer than one month.     

Parallel and serial dual electrode detectors for capillary electrophoresis

Application of parallel and serial dual electrode detectors for capillary electrophoresis was first described. In parallel dual electrode approach, two 100 μm-diameter Cu disks arranged side by side were used as the dual working electrode for the simultaneous determination of a mixture of carbohydrates and amino acids. In serial dual electrode approach, two working electrodes were arranged in a disk-ring manner for the simultaneous determination of both cysteine and cystine; the disk electrode was Hg/Au serving as the upstream electrode, the ring electrode was 5% CoPC carbon paste serving as the downstream electrode.     

方波伏安法测定新型修饰多壁碳纳米管糊电极对肼的电催化氧化(英文)

The application of p-aminophenol as a suitable mediator, as a sensitive and selective voltammetric sensor for the determination of hydrazine using square wave voltammetric method were described. The modified multiwall carbon nanotubes paste electrode exhibited a good electrocatalytic activity for the oxidation of hydrazine at pH = 7.0. The catalytic oxidation peak currents showed a linear dependence of the peaks current to the hydrazine concentrations in the range of 0.5–175 μmol/L with a correlation coefficient of 0.9975. The detection limit (S/N = 3) was estimated to be 0.3 μmol/L of hydrazine. The relative standard deviations for 0.7 and 5.0 μmol/L hydrazine were 1.7 and 1.1%, respectively. The modified electrode showed good sensitivity and selectivity. The diffusion coefficient (D = 9.5 × 10–4 cm2/s) and the kinetic parameters such as the electron transfer coefficient (α = 0.7) of hydrazine at the surface of the modified electrode were determined using electrochemical approaches. The electrode was successfully applied for the determination of hydrazine in real samples with satisfactory results.     

以3,4-二羟基肉桂酸为介质的多壁碳纳米管糊电极用于检测药物和尿液样品中的谷胱甘肽(英文)

A sensitive and selective electrochemical sensor for the determination of glutathione(GSH) was developed using a modified multiwall carbon nanotube paste electrode with 3,4 dihydroxy cinnamic acid as a mediator.This modified electrode showed very high electrocatalytic activity for the anodic oxidation of GSH.Under the optimized conditions,the electrocatalytic peak current showed a linear relationship with GSH concentration in the range of 0.5-400.0 μmol/L with a detection limit of 0.1 μmol/L GSH.The relative standard deviations for seven successive assays of 5.0 and 25.0 μmol/L GSH were 2.2% and 2.7%,respectively.The modified electrode was used for the determination of GSH compounds in real urine samples.     

Simple Method for Simultaneous Quantitation and Fingerprint Analysis of Ginkgo biloba Tablets by High Performance Liquid Chromatography-UV-Evaporative Light Scattering Detector

By optimizing the separation and analytical conditions, a reliable, simple and accurate high-performance liquid chromatography(HPLC) method coupled with ultraviolet(UV) and evaporative light scattering detector(ELSD) was developed for the simultaneous determination of lactones and flavonoid, that is, bilobalide, ginkgolide A, ginkgolide B, and rutin, in more than 10 batches of Ginkgo biloba tablets from different pharmaceutical companies. The method could also be applied to fingerprint research, for a more general evaluation of the quality of this preparation. The separation of the components was achieved on a Hanbon C18 column with gradient elution using water and methanol containing 0.1% trifluoroacetic acid(TFA). The column temperature was 30 ℃ and the flow-rate of the mobile phase was 0.6 mL/min. The drift tube temperature of the ELSD was set at 100 ℃, and the nitrogen flow-rate was 2 L/min. Good linear relationships were shown with correlation coefficients for analytes exceeding 0.9913. The limits of detection(LODs, S/N=3) and the limits of quantitation(LOQs, S/N=10) were 0.00887--0.0508 μg/μL and 0.0171-0.0636 μg/μL, respectively, on the column. The relative standard deviations(RSD) of the analytes were less than 3.61% for intraday and 3.70% for interday, respectively. The average recovery rates obtained were in the range of (97.3±4.3)% to (101.9±3.1)% for all the compounds. The results of quantitative and fingerprint analysis proved that the contents of the components were totally similar in the preparation of Ginkgo biloba tablets from the same pharmaceutical company; whereas, they varied significantly in the preparations of Ginkgo biloba tablets from different companies.     

Simple and cost-effective determination of ciprofloxacin hydrochloride by electrical micro-titration

By employing an electrical micro-titration system, in which a capacitively coupled contactless conductivity detector(C4D) was used to monitor the reaction process in real time, herein a novel method for determining ciprofloxacin hydrochloride(CIPHCl) was developed for the first time. Mode 1: Standard CIPHCl solutions at different concentrations were loaded into reaction cells, respectively, and were titrated with standard Ag+. Upon the titration, the formation of a precipitate alters the number of ions in the solution, raising the change of conductivity, which was monitored by a special C~4 D to construct a titration curve. The endpoint of the titration was located from the peak of the curve. Between the elapsed time and the initial concentration of titrand, a linear relationship was established over the range of2.0–8.0 mmol/L. Mode 2: Standard Fe~(3+) took the place of Ag~+, and was used as titrant to recognize ciprofloxacin contributed to the formation of complexation, which also resulting a change of solution conductivity. Under optimized conditions, a working range of 1.0–5.0 mmol/L CIPHCl was found. Because the reaction solutions were isolated from the working electrodes, this pioneer work shows significant simplicity and cost-effectiveness, by eliminating the requirements for detector exchange/renewal between different measurements, and by involving no auxiliary chemicals. Both of the two approaches were applied successfully to determine CIPHCl in tablet samples. And the results were in good agreement with those obtained by reference method.     

用聚(L-蛋氨酸)/纳米金修饰玻碳电极同时灵敏检测多巴胺和尿酸(英文)

A novel electrochemical sensor was fabricated by electrodeposition of gold nanoparticles on a poly(L-methionine)(PMT)-modified glassy carbon electrode(GCE) to form a nano-Au/PMT composite-modified GCE(nano-Au/PMT/GCE).Scanning electron microscopy and electrochemical techniques were used to characterize the composite electrode.The modified electrode exhibited considerable electrocatalytic activity towards the oxidation of dopamine(DA) and uric acid(UA) in phosphate buffer solution(pH = 7.00).Differential pulse voltammetry revealed that the electrocatalytic oxidation currents of DA and UA were linearly related to concentration over the range of 5.0 ×10–8 to 10–6 mol/L for DA and 7.0 × 10–8 to 10–6 mol/L for UA.The detection limits were 3.7 × 10–8mol/L for DA and 4.5 × 10–8 mol/L for UA at a signal-to-noise ratio of 3.According to our experimental results,nano-Au/PMT/GCE can be used as a sensitive and selective sensor for simultaneous determination of DA and UA.     

2,3-Dimercaptosuccinic acid self-assembled gold electrode for the simultaneous determination of epinephrine and dopamine

Simultaneous determination of epinephrine(EP)and dopamine(DA)at 2,3-dimercaptosuccinic acid(DMSA)modified electrode was studied.The oxidation peaks of the mixture of EP and DA appeared at the same potential,but the cathodic peak currents were only linear to the concentration of DA,whereas the anodic peak currents were equal to the sum of individual anodic peak currents of EP and DA.Therefore,a novel electrochemical method for the simultaneous determination of EP and DA at a DMSA modified electrode(DMSA/A...     

An end-channel amperometric detector for microchip capillary electrophoresis

An end-channel amperometric detector with a guide tube for working electrode was designed and integrated on a home-made glass microchip. The guide tube was directly patterned and fabricated at the end of the detection reservoir, which made the fixation and alignment of working electrode relatively easy. The fabrication was carried out in a two-step etching process. A 30 μm carbon fiber microdisk electrode and Pt cathode were also integrated onto the amperometric detector. The characteristics and primary performance of the home-made microchip capillary electrophoresis (MCCE) were investigated with neurotransmitters. The baseline separation of dopamine (DA), catechol (CA) and epinephrine (EP) was achieved within 80 s. Separation parameters such as injection time, buffer components, pH of the buffer were studied. Relative standard deviations of not more than 6.0% were obtained for both peak currents and migration times. Under the selected separation conditions, the response for DA was linear from 5 to 200 μM and from 20 to 800 μM for CA. The limits of detection of DA and CA were 0.51 and 2.9 μM, respectively (S/N=3).     

A high-performance polycarbonate electrophoresis microchip with integrated three-electrode system for end-channel amperometric detection

A fully integrated polycarbonate (PC) microchip for CE with end-channel electrochemical detection operated in an amperometric mode (CE-ED) has been developed. The on-chip integrated three-electrode system consisted of a gold working electrode, an Ag/AgCl reference electrode and a platinum counter electrode, which was fabricated by photo-directed electroless plating combined with electroplating. The working electrode was positioned against the separation channel exit to reduce post-channel band broadening. The electrophoresis high-voltage (HV) interference with the amperometric detection was assessed with respect to detection noise and potential shifts at various working-to-reference electrode spacing. It was observed that the electrophoresis HV interference caused by positioning the working electrode against the channel exit could be diminished by using an on-chip integrated reference electrode that was positioned in close proximity (100 microm) to the working electrode. The CE-ED microchip was demonstrated for the separation of model analytes, including dopamine (DA) and catechol (CA). Detection limits of 132 and 164 nM were achieved for DA and CA, respectively, and a theoretical plate number of 2.5x10(4)/m was obtained for DA. Relative standard deviations in peak heights observed for five runs of a standard solution containing the two analytes (0.1 mM for each) were 1.2 and 3.1% for DA and CA, respectively. The chip could be continuously used for more than 8 h without significant deterioration in analytical performance.     

In-channel modification of electrochemical detector for the detection of bio-targets on microchip

The coulometric efficiency (C_eff) of an amperometric detector integrated on PDMS/glass capillary electrophoresis microfluidic device (microchip) has been enhanced by in-channel electrochemical modification. In-channel electrochemical deposition of gold particles was performed in order to vertically increase the surface area of the Au sensing microelectrode. The roughness of the electrodes was characterized using scanning electron microscopy and profilometric analysis. The degree of electrode modification was also characterized by roughness factor determination. Separation processes including detection potential was optimized and the analytical performance of the microchip was tested using a mixture of dopamine (DA) and catechol (CA). The modified electrochemical detector provided well-resolved separation of DA and CA in less than 60 s with enhanced sensitivity; no peak broadening was observed. The limit of detection using in-channel modification of working electrode for DA and CA are 60 and 110 nM, respectively. Thus, in-channel electrochemical deposition of metallic particles should be used to enhance the C_eff of integrated amperometric detection of analytes with good redox properties in order to obtain lower LODs.     

新型安培检测毛细管电泳微系统

将电极、６ｃｍ分离毛细管、缓冲池、检测池集成于８．４×５．０ｃｍ有机玻璃片上,制作了一个毛细管电泳微系统。以碳纤维微盘电极作为工作电极,采用三电极体系柱端检测了１×１０－４ｍｏｌ／Ｌ多巴胺（ＤＡ）,具有良好的重现性,检测限３．６×１０－８ ｍｏｌ／Ｌ,线性范围５×１０－７～１×１０－４ｍｏｌ／Ｌ,并在该系统上分离了邻苯二酚（ＣＡ）和多巴胺的混合物。     

Simple amperometric detector for microchip capillary electrophoresis, and its application to the analysis of dopamine and catechol

We report on a simple amperometric detector for use in microchip capillary electrophoresis. A disposable syringe serves as the electrode holder that is fixed at the outlet of the separation channel. A carbon paste electrode is used to detect dopamine (DA) and catechol (CA) after electrophoretic separation. The two model analytes were well separated within 60 s. The response is linear in the concentration range from 4 to 500???M, and the detection limit is 1.2???M for DA (S/N = 3:1). The relative standard deviations of the inter-run and inter-electrode peak currents, respectively, are 2.8% and 5.7% for DA, and 3.9% and 6.5% for CA. Favorable column efficiency (expressed by the theoretical plate number which is 5.3 × 104 m^-1 for DA) is achieved. The method was successfully applied to the separation and detection of 3-aminophenol (3-AP) in an injection powder containing sodium 4-aminosalicylate. The detection limit of 3-AP is as low as 1.7???M, which meets the demand of the impurity test. The facile assembly allows convenient replacement of working electrodes and improves the longevity of the microanalytical system.

Graphene/poly(ethylene‐co‐vinyl acetate) composite electrode fabricated by melt compounding for capillary electrophoretic determination of flavones in Cacumen platycladi

In this report, a graphene/poly(ethylene‐co‐vinyl acetate) composite electrode was fabricated by melt compounding for the amperometric detection of capillary electrophoresis. The composite electrode was fabricated by packing a mixture of graphene and melted poly(ethylene‐co‐vinyl acetate) in a piece of fused silica capillary under heat. The structure of the composite was investigated by scanning electron microscopy and Fourier transform infrared spectroscopy. The results indicated that graphene sheets were well dispersed in the composite to form an interconnected conducting network. The performance of this unique graphene‐based detector has been demonstrated by separating and detecting rutin, quercitrin, kaempferol, and quercetin in Cacumen platycladi in combination with capillary electrophoresis. The four flavones have been well separated within 9 min in a 50‐cm‐long capillary at a separation voltage of 12 kV using a 50 mM sodium borate buffer (pH 9.2). The graphene‐based detector offered significantly lower operating potentials, substantially enhanced signal‐to‐noise characteristics, lower expense of operation, high resistance to surface fouling, and enhanced stability. It showed long‐term stability and repeatability with relative standard deviations of <5% for the peak current (n = 15).     

Three‐Electrode‐Integrated Sensor into a Micropipette Tip

This work describes the construction, characterization, and application of a three‐electrode‐integrated sensor into a micropipette tip. The three electrodes (working, pseudoreference and counter) are positioned at the end of a micropipette tip. The working electrode (graphite composite or gold microfiber) is placed inside the micropipette tip and the pseudo‐reference and counter electrodes outside (diametrically opposed sides). This approach is candidate for portable applications and allows the analysis and studies in low‐volume solutions (ca. 10 µL) which are useful for waste minimization and development of clean analytical methods. In addition, the three‐electrode‐integrated sensor can be easy used as detector in flow injection system through its direct joining at the end of polyethylene tubing of the FIA system.     

Flow‐Injection Amperometric Method for Indirect Determination of Dopamine in the Presence of a Large Excess of Ascorbic Acid

A simple flow injection amperometric system for fast and indirect quantification of dopamine (DA) in the presence of a large excess of ascorbic acid (AA) is reported. The method consists of the application of three sequential potential pulses to an unmodified glassy carbon‐working electrode positioned in a wall‐jet cell. DA is indirectly detected at +0.35 V through the reduction of the oxidation product (o‐dopaminoquinone) electrochemically generated at +0.80 V. The third potential pulse (0.00 V) is applied for the regeneration (cleaning) of the unmodified working electrode. The limits of detection (LOD) and quantification (LOQ) were calculated as 50 and 170 nmol L^?1, respectively. Considering the LOQ value, the present methodology allows DA quantification in the presence up to 5000‐fold more of AA (1.0 mmol L^?1).     

Selective Detection of Dopamine and Its Metabolite,DOPAC, in the Presence of Ascorbic Acid Using Diamond Electrode Modified by the Polymer Film

The surface of boron‐doped diamond (BDD) electrode is modified by the polymer film for the first time. The cationic polymer film of N,N‐dimethylaniline (DMA) is electrochemically deposited on BDD electrode surface. This polymer (PDMA) film‐coated BDD electrode is used as a sensor which selectively detect dopamine (DA) in the presence of ascorbic acid (AA). This electrode also can detect both DA and its metabolite, 3,4‐dihydroxy phenyl acetic acid (DOPAC) in the presence of AA in the range of the physiological concentrations of these species. Favorable ionic interaction (i.e., electrostatic attraction) between the PDMA film and AA or DOPAC lowers their oxidation potentials and enhances the current response for AA and DOPAC compared to that at the bare electrode. The PDMA film also shows a hydrophobic interaction with DA and DOPAC. In cyclic voltammetric measurements, the PDMA film‐coated electrode can successfully separate the oxidation potentials for AA and DA coexisting in the same solution and the separation is about 200 mV. AA oxidizes at more negative potential than DA. In square‐wave voltammetry, the sensitivity of the PDMA film‐coated BDD electrode for DA in the presence of higher concentration of AA is higher than that of the PDMA film‐coated glassy carbon electrode. The hydrodynamic amperometric experiments confirm that the oxidation of AA is not affected by the oxidized product of DA and vice versa. So, unlike the bare electrode the catalytic oxidation of AA by the oxidized DA is eliminated at the PDMA film‐coated BDD electrode. The sensitivities of the modified electrode for AA, DA and DOPAC, which are present in the same solution with their physiological concentration ratios, are calculated to be 0.070, 0.363 and 0.084 μA μM^?1, respectively. The modified electrode exhibits a stable and sensitive response to DA.     

Amperometric L‐cysteine Sensor Using a Gold Electrode Modified with Thiolated Catechol

A thiolated catechol (CA) consisting of 1,6‐Hexanedithiol (HDT) and CA was modified on a gold (Au) electrode to obtain an amperometric L‐cysteine sensor with detection limit of 60.6 nM. The preparation of thiolated CA was conducted via a thiol addition between HDT and electro‐oxidized CA (EOCA). Briefly, the thiol addition reaction was accomplished by potential cycling of HDT/Au electrode in 0.1 M phosphate buffer (PB, pH 7.2) containing CA, and an EOCA‐HDT/Au electrode was produced. The obtained EOCA‐HDT/Au electrode exhibits a pair of well‐defined redox peaks (at 0.22/0.10 V) of o‐quinone moiety, which effectively mediates the oxidation of L‐cysteine in a 0.1 M PB (pH 7.2), with an over‐potential decrease by ca. 0.12 V (versus bare Au electrode). Electrochemical quartz crystal microbalance, cyclic voltammetry and surface‐enhanced Raman spectra were used to study relevant processes and/or film properties. The amperometric L‐cysteine sensor has good anti‐interferent ability and reproducibility. It also has acceptable recovery for detection of L‐cysteine in urine samples.