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Separation Voltage (separation + voltage)
Selected AbstractsSeparation and Detection of Nitrophenols at Capillary Electrophoresis Microchips with Amperometric DetectionELECTROANALYSIS, Issue 2 2006Jan Fischer Abstract A miniaturized analytical system for the separation and amperometric detection of toxic nitrophenols, based on the coupling of a micromachined capillary electrophoresis (CE) chip with a glassy carbon detector is described. This microsystem enables a rapid (120,s/sample) simultaneous determination of five priority nitrophenolic pollutants (2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, and 2-methyl-4,6-dinitrophenol). These compounds can be detected down to the 1×10,5,M level using a 15,mM phosphate buffer pH,7.2 (containing 1.3,mM ,-cyclodextrin) as running solution on 77,mm long microchannel by applying a separation voltage of 3000,V and a negative potential of ,0.7,V (vs. Ag /AgCl wire). Applicability to ground water samples was demonstrated. [source] Electrochemical Detection for Capillary Electrophoresis Microchips: A ReviewELECTROANALYSIS, Issue 13 2005Joseph Wang Abstract Electrochemistry detection offers considerable promise for capillary-electrophoresis (CE) microchips, with features that include remarkable sensitivity, portability, independence of optical path length or sample turbidity, low cost and power requirements, and high compatibility with modern micromachining technologies. This article highlights key strategies in controlled-potential electrochemical detectors for CE microchip systems, along with recent advances and directions. Subjects covered include the design of the electrochemical detection system, its requirements and operational principles, common electrode materials, isolation from the separation voltage, derivatization reactions, typical applications, and future prospects. It is expected that electrochemical detection will become a powerful tool for CE microchip systems and will lead to the creation of truly portable (and possibly disposable) devices. [source] Simultaneous determination of memantine and amantadine in human plasma as fluorescein derivatives by micellar electrokinetic chromatography with laser-induced fluorescence detection and its clinical applicationELECTROPHORESIS, Issue 11 2010Hsin-Hua Yeh Abstract A nonionic surfactant MEKC method with LIF detection was developed for the simultaneous determination of memantine, an anti-Alzheimer's disease agent, and amantadine, an anti-Parkinson's disease drug, in human plasma. Before analysis, the plasma samples were pretreated by liquid,liquid extraction with ethyl acetate, and derivatized with 6-carboxyfluorescein N -hydroxysuccinimide ester. The chemical derivatization is performed with 6-carboxyfluorescein N -hydroxysuccinimide ester in ACN , 5,mM pH 9.0 borate buffer (40:60, v/v) at 35°C for 3,h. After the derivatization reaction, hydrodynamic injection (0.5,psi, 8,s) was used to introduce the derivatized solution, and the separation was performed in borate buffer (30,mM, pH 9.5) with the nonionic surfactant Brij-35® (0.07%, w/v); the separation voltage was 6,kV. The linear ranges of the method for the determination of memantine and amantadine in human plasma were over a range of 2.0,60.0,ng/mL. The detection limit was 0.5,ng/mL (S/N=3). This method was applied successfully to monitor the concentration of memantine or amantadine in patients with Alzheimer's disease or Parkinson's disease. [source] MCE enzyme immunoassay for carcinoembryonic antigen and alpha-fetoprotein using electrochemical detectionELECTROPHORESIS, Issue 19 2009Shusheng Zhang Abstract An MCE electrochemical enzyme immunoassay protocol for the determination of carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP) was reported. Two antigens (Ag), CEA and AFP, were incubated simultaneously with an excess amount of horseradish peroxidase-labeled antibody (Ab*). The free Ab* and the Ab*,Ag complex produced in the solution were first separated through a postcolumn reaction and then traced by the enzyme substrate o -aminophenol. The 3-aminophenoxazine produced in enzyme reaction was detected with downstream amperometric detection. The separations were performed at a separation voltage of +1.4,kV and were completed in less than 60,s. The better analytical performance and distinct miniaturization/portability for MCE at less assay time and sample volume consumption was achieved. The detection limit of CEA and AFP was calculated to be 0.25 and 0.13,ng/mL, respectively. Therefore, MCE could be used as a sensitive and new tool in separation science and offered considerable promise in biological sample analysis or quick clinical diagnosis. [source] Determination of thyreostatics in animal feeds by CE with electrochemical detectorELECTROPHORESIS, Issue 19 2009Dexian Kong Abstract A simple, rapid, reproducible and sensitive method based on CE with electrochemical detector was developed for the simultaneous determination of five thyreostatics including 2-thiouracil (TU), 6-methyl-2-thiouracil (MTU), 6-propyl-2-thiouracil (PTU), 6-phenyl-2-thiouracil (PhTU) and methimazole (TAP) in animal feeds. A home-made wall-jet electrochemical detector with a 300,,m diameter platinum-disk-working electrode was equipped at the end of separation capillary and used to detect oxidation currents of these thyreostatics. Under the optimum experimental conditions, TU, MTU, PTU, PhTU and TAP could be well separated within 15,min at the separation voltage of 16,kV in 20,mmol/L sodium borate buffer (pH 9.2). The detection limits (S/N=3) of the five thyreostatics in animal feeds were found to be 7.6,,g/kg for TAP, 25,,g/kg for PTU, 15,,g/kg for PhTU, 18,,g/kg for TU and 20,,g/kg for MTU by the developed CE with electrochemical detector method coupled with solid-phase extraction sample pretreatment technique. [source] Fast derivatization of the non-protein amino acid ornithine with FITC using an ultrasound probe prior to enantiomeric determination in food supplements by EKCELECTROPHORESIS, Issue 6 2009Elena Domínguez-Vega Abstract An EKC method for the determination of ornithine (Orn) enantiomers has been developed after a fast pre-capillary derivatization with FITC. The derivatization step was needed to provide a chemical moiety to the Orn molecule, enabling a sensitive UV detection and the interaction with the CDs used as chiral selectors. To accelerate the derivatization reaction, an ultrasound probe was used. For the development of the chiral method, the influence of different experimental conditions (type and concentration of the chiral selector, temperature, and separation voltage) was investigated. Due to the anionic nature of the analyte (FITC-Orn), five neutral CDs were employed as chiral selectors. The native ,-CD showed the highest chiral separation power, observing that a low concentration of this CD (1,mM), using a working temperature of 25°C and a separation voltage of 20,kV, enabled to obtain the highest enantioresolution for Orn and its separation from other amino acids usually present in food supplements. After optimizing the method for the preconditioning of the capillary, the analytical characteristics of the chiral method were established. Linearity, LOD and LOQ, precision, and accuracy were evaluated previously to the determination of Orn enantiomers contained in ten commercial food supplements. No interferences from other amino acids present in these samples were observed. [source] Separation of cytokinin isomers with a partial filling-micellar electrokinetic chromatography-mass spectrometry approachELECTROPHORESIS, Issue 10 2008Liya Ge Abstract A new method based on partial filling-MEKC (PF-MEKC) directly coupled to ESI-MS was developed for the simultaneous separation and determination of 13 structurally similar cytokinins, including various geometric and positional isomers of cytokinins. On the basis of the resolution of the neighboring isomer peaks, different parameters (i.e., pH and concentration of buffer, surfactant concentrations, length of the injected micellar plug, organic modifier, and applied separation voltage) were optimized to achieve a satisfactory PF-MEKC separation. Under optimum conditions, the separation of 13 cytokinin standards was accomplished within 25,min. MS/MS with multiple reaction monitoring detection was carried out to obtain sufficient selectivity. PF-MEKC-MS/MS allowed for the direct identification and confirmation of the cytokinins present in banana (Musa spp.) pulp sample after extraction and purification. Finally, trans- zeatin riboside (ZR) and trans- zeatin (Z) were unambiguously identified in banana pulp. It is anticipated that the current PF-MEKC-MS method can be applied to analyze cytokinins in a wide range of biological samples. [source] Analyses of gibberellins in coconut (Cocos nucifera L.) water by partial filling-micellar electrokinetic chromatography-mass spectrometry with reversal of electroosmotic flowELECTROPHORESIS, Issue 10 2008Liya Ge Abstract In this paper, we present the results of simultaneous screening of eight gibberellins (GAs) in coconut (Cocos nucifera L.) water by MEKC directly coupled to ESI-MS detection. During the development of MEKC-MS, partial filling (PF) was used to prevent the micelles from reaching the mass spectrometer as this is detrimental to the MS signal, and a cationic surfactant, cetyltrimethylammonium hydroxide, was added to the electrolyte to reverse the EOF. On the basis of the resolution of the neighboring peaks, different parameters (i.e., the pH and concentration of buffer, surfactant concentrations, length of the injected micellar plug, organic modifier, and applied separation voltage) were optimized to achieve a satisfactory PF-MEKC separation of eight GA standards. Under optimum conditions, a baseline separation of GA standards, including GA1, GA3, GA5, GA6, GA7, GA9, GA12, and GA13, was accomplished within 25,min. Satisfactory results were obtained in terms of precision (RSD of migration time below 0.9%), sensitivity (LODs in the range of 0.8,1.9,,M) and linearity (R2 between 0.981 and 0.997). MS/MS with multiple reaction monitoring (MRM) detection was carried out to obtain sufficient selectivity. PF-MEKC-MS/MS allowed the direct identification and confirmation of the GAs presented in coconut water (CW) sample after SPE, while, the quantitative analysis of GAs was performed by PF-MEKC-MS approach. GA1 and GA3 were successfully detected and quantified in CW. It is anticipated that the current PF-MEKC-MS method can be applicable to analyze GAs in a wide range of biological samples. [source] On-line sample stacking and short-end injection CE for the determination of fluoxetine and norfluoxetine in plasma: Method development and validation using experimental designsELECTROPHORESIS, Issue 18 2007Chia-Chia Lu Abstract A short-end injection CE method combining field-amplified sample stacking (FASS) is presented for the analysis of fluoxetine (FL) and norfluoxetine in plasma. In this study, FASS enhanced the sensitivity about 1100-fold, while short-end injection reduced the analysis time to less than 4,min. Parameters involved in the separations were investigated using a central composite design (CCD) and response surface methodology to optimize the separation conditions in a total of only 32 runs. Samples injected into the capillary for 99.9,s at a voltage of ,5,kV were stacked in a water plug (0.5,psi, 9,s). Baseline resolution of FL and its major metabolite was achieved using a BGE formulation consisting of phosphate,triethanolamine at low pH, and a separation voltage of ,10,kV. Five percent methanol was added as organic modifier to enhance selectivity and resolution. The linear range was between 10 and 500,ng/mL (r >0.9946), covering the expected plasma therapeutic ranges. The LOD in plasma were 4,ng/mL (S/N,=,3), a value comparable to that obtained using LC-MS, showing the success of the on-line stacking technique. Our method was also successfully validated in quantification and pharmacokinetic studies with three volunteer plasma samples and could be applied to pharmacogenetic studies. [source] Development of a new method for analysis of Sudan dyes by pressurized CEC with amperometric detectionELECTROPHORESIS, Issue 11 2007Shaofeng Liu Abstract A new analytical method, pressurized CEC (pCEC) with amperometric detection (AD) using 1.5,,m RP nonporous silica packed columns has been developed for the rapid separation and determination of four Sudan dyes in hot chilli. The influence of several experimental parameters on the retention behavior has been investigated. The electrochemical oxidation of Sudans I,IV separated by pCEC can be reliably monitored with a carbon electrode at +0.95,V (vs. Ag/AgCl). Fast and efficient separation of the analytes was achieved within 7,min by pCEC under the optimum conditions with an ACN/water (95:5%) mobile phase containing formic acid (pH,4.3), 5% acetone and 0.002% triethylamine using a separation voltage of 12,kV. The detection limits for four Sudan dyes ranged from 8.0,×,10,7 to 1.2,×,10,6,mol/L. To evaluate the feasibility and reliability of this method, the proposed pCEC-AD method was further demonstrated with hot chilli samples spiked with Sudan dyes. [source] Carbon nanotube/poly(methyl methacrylate) composite electrode for capillary electrophoretic measurement of honokiol and magnolol in Cortex Magnoliae OfficinalisELECTROPHORESIS, Issue 16 2006Xiao Yao Abstract This paper describes the development and the application of a novel carbon nanotube/poly(methyl methacrylate) (CNT/PMMA) composite electrode as a sensitive amperometric detector of CE. The composite electrode was fabricated on the basis of the in,situ polymerization of a mixture of CNT and prepolymerized methylmethacrylate in the microchannel of a piece of fused-silica capillary under heat. The performance of this unique system has been demonstrated by separating and detecting honokiol and magnolol in traditional Chinese medicine, Cortex Magnoliae Officinalis. Factors influencing their separation and detection processes were examined and optimized. Honokiol and magnolol were well separated within 7,min in a 40 cm long capillary at a separation voltage of 15,kV using a 50 mM borate buffer (pH,9.2). The new CNT-based CE detector offered significantly lower operating potentials, yielded substantially enhanced S/N characteristics, and exhibited resistance to surface fouling and hence enhanced stability. It demonstrated long-term stability and reproducibility with RSDs of less than 5% for the peak current (n = 9) and should also find a wide range of applications in microchip CE, flowing injection analysis, and other microfluidic analysis systems. [source] Enhanced separation of purine and pyrimidine bases using carboxylic multiwalled carbon nanotubes as additive in capillary zone electrophoresisELECTROPHORESIS, Issue 16 2006Xin Xiong Abstract This paper describes the enhanced separation of adenine (A), hypoxanthine (HX), 8-azaadenine (8-AA), thymine (T), cytosine (C), uracil (U) and guanine (G) by CZE dispersing carboxylic multiwalled carbon nanotubes (c-MWNTs) into the running buffer. The effect of important factors such as c-MWNT nanoparticle concentration, the acidity and concentration of running buffer, and separation voltage were investigated to acquire the optimum conditions. The seven purine and pyrimidine bases could be well separated within 16,min in a 35,cm effective length fused-silica capillary at a separation voltage of +8.0,kV in a 23,mM tetraborate buffer (pH,9.2) containing 8.0×10,5,g/mL c-MWNTs. Under the optimal conditions, the linear ranges were of 2,250,,g/mL for A (R2,=,0.995), 3,200,,g/mL for U (R2,=,0.990) and G (R2,=,0.992), 3,250,,g/mL for T (R2,=,0.998), 2,200,,g/mL for C (R2,=,0.985) and 4,200,,g/mL for HX (R2,=,0.988) and 8-AA (R2,=,0.990). The detection limits were 0.9,,g/mL for A (S/N,=,3), 2.4,,g/mL for U, 2.0,,g/mL for T, 1.5,,g/mL for C, 2.5,,g/mL for G and 3.0,,g/mL for HX and 8-AA. The proposed method was successfully applied for determining five purine and pyrimidine bases in yeast RNA. [source] Development of off-line and on-line capillary electrophoresis methods for the screening and characterization of adenosine kinase inhibitors and substratesELECTROPHORESIS, Issue 12 2006Jamshed Iqbal Abstract Fast and convenient CE assays were developed for the screening of adenosine kinase,(AK) inhibitors and substrates. In the first method, the enzymatic reaction was performed in a test tube and the samples were subsequently injected into the capillary by pressure and detected by their UV absorbance at 260,nm. An MEKC method using borate buffer (pH,9.5) containing 100,mM SDS (method,A) was suitable for separating alternative substrates (nucleosides). For the CE determination of AMP formed as a product of the AK reaction, a phosphate buffer (pH,7.5 or 8.5) was used and a constant current (95,,A) was applied (method,B). The methods employing a fused-silica capillary and normal polarity mode provided good resolution of substrates and products of the enzymatic reaction and a short analysis time of less than 10,min. To further optimize and miniaturize the AK assays, the enzymatic reaction was performed directly in the capillary, prior to separation and quantitation of the product employing electrophoretically mediated microanalysis (EMMA, method,C). After hydrodynamic injection of a plug of reaction buffer (20,mM Tris-HCl, 0.2,mM MgCl2, pH,7.4), followed by a plug containing the enzyme, and subsequent injection of a plug of reaction buffer containing 1,mM,ATP, 100,,M adenosine, and 20,,M,UMP as an internal standard,(I.S.), as well as various concentrations of an inhibitor, the reaction was initiated by the application of 5,kV separation voltage (negative polarity) for 0.20,min to let the plugs interpenetrate. The voltage was turned off for 5,min (zero-potential amplification) and again turned on at a constant current of ,60,,A to elute the products within 7,min. The method employing a polyacrylamide-coated capillary of 20,cm effective length and reverse polarity mode provided good resolution of substrates and products. Dose,response curves and calculated Ki values for standard antagonists obtained by CE were in excellent agreement with data obtained by the standard radioactive assay. [source] On-line concentration of proteins in pressurized capillary electrochromatography coupled with electrospray ionization-mass spectrometryELECTROPHORESIS, Issue 7-8 2005Zhen Liang Abstract Pressurized capillary electrochromatography (pCEC) and electrospray ionization-mass spectrometry (ESI-MS) have been hyphenated for protein analysis. Taken cytochrome,c, lysozyme, and insulin as samples, the limits of detection (LODs) for absolute concentrations are 10,11,mol (signal-to-noise ratio S/N = 3) with relative standard deviations (RSDs) of retention time and peak area, respectively, of less than 1.7% and 4.8%. In order to improve the detection sensitivity, on-line concentration by field-enhanced sample-stacking effect and chromatographic zone-sharpening effect has been developed, and parameters affecting separation and detection, such as pH and electrolyte concentration in the mobile phase, separation voltage, as well as enrichment voltage and time, have been studied systematically. Under the optimized conditions, the LODs of the three proteins could be decreased up to 100-fold. In addition, the feasibility of such techniques has been further demonstrated by the analysis of modified insulins at a concentration of 20,,g/mL. [source] The influence of polymer concentration, applied voltage, modulation depth and pulse frequency on DNA separation by pulsed field CEJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17-18 2010Zhenqing Li Abstract DNA fragments (0.1,10,kbp (kbp, kilo base pair)) separation by square-wave pulsed field CE in hydroxyethylcellulose (HEC, 1300,K) polymer was performed in this work. The effects of polymer concentration, pulse field strength, pulse frequency and modulation depth were investigated. We found that low HEC (about 0.1%) concentration is suitable for the separation of small DNA fragments (<1,kbp), whereas higher HEC concentration (>0.5%) is appropriated for high-mass DNA molecular (>1,kbp) separation. The mobility of DNA fragments is nearly linearly related to average separation voltage under pulsed field conditions. Higher modulation depth is suited to separate the longer DNA fragments and lower modulation depth favors the resolution of short DNA fragments. Thus, the intermediate modulation depth (100%) and pulse frequency (about 31.3,Hz) are prerequisite for high-resolution DNA separation. [source] Rapid screening of beta-adrenergic agents and related compounds in human urine for anti-doping purpose using capillary electrophoresis with dynamic coatingJOURNAL OF SEPARATION SCIENCE, JSS, Issue 20 2009Monica Mazzarino Abstract This paper presents a capillary electrophoresis method, developed for the detection, in human urine, of beta-adrenergic agents and phenolalkylamines. The electrophoretic separation is achieved in less than 10 min and is based on the use of CEofix kit, for the dynamic capillary coating. The effects of accelerator buffer pH and separation voltage were investigated. The optimum buffer pH was found to be 2.5 for beta2-agonists and 6.2 for beta-blockers and phenoalkylamines with a separation voltage of 15 kV. Urine samples spiked with the compounds here studied were treated according to the standard procedure (SPE and evaporation to dryness) and analyzed by CE interfaced with an UV diode-array, set at 195 and 210 nm. The quantitative validation results, obtained analyzing samples at three different concentrations, show a good precision of peak areas that do not exceed 5% for intra-day assays and 10% for inter-day assays. Good linearity (r2 > 0.995) was obtained within the 50,500 ng/mL concentration range. The qualitative validation data show a relative migration times (MTs) variation lower than 1%. The analytes were clearly distinguishable in urine, with LOD and LOQ in the range of 10,80 and 40,100 ng/mL, respectively. [source] Effect of stability of internal standard on quantification of 15 flavonoids in Epimedium using CZEJOURNAL OF SEPARATION SCIENCE, JSS, Issue 2 2009Xiao-jia Chen Abstract A CZE method was developed for the simultaneous determination of 15 flavonoids, including epimedin B, epimedin A, hexandraside F, epimedin C, icariin, sagittatoside B, sagittatoside A, hexandraside E, 2,,- O -rhamnosyl icariside II, baohuoside VII, baohuoside I, caohuoside C, epimedoside C, baohuoside II, and kaempferol-3- O -rhamnoside, in different species of Epimedium, and the effect of stability of internal standard (IS) on quantification was also investigated. As a result, rutin was not available for use as an IS because of its unstable property in sample solution, which suggested that the stability of IS both in standards and sample solution should be considered for the analysis. Using stable daidzein as IS, the analysis was performed within 35 min by using 50 mM borax buffer containing 20% ACN as a modifier (pH 10.0), while separation voltage was 25 kV and temperature was at 30°C. The method was validated to be accurate, simple, and repeatable, and was successfully applied to the analysis of 36 samples from 17 species of Epimedium. [source] Preliminary study on the monitoring of glutathione S-tranferase activity toward styrene oxide by electromigration methodsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 12 2005ková Abstract A new method has been developed for the monitoring of glutathione S-tranferase (GST) detoxification activity toward styrene oxide (SO). The enzymatic reaction was carried out directly in a thermostatted autosampler vial and the formation of conjugates between glutathione (GSH) and SO was monitored by sequential MEKC runs. The determinations were performed in a 50-,m fused silica capillary using 50 mM SDS in 20 mM phosphate 20 mM tetraborate buffer (pH 8.3) as a background electrolyte; separation voltage 28 kV (positive polarity), temperature of capillary 25°C, and detection at 200 nm. The method is rapid, amenable to automation, and requires only small amounts of samples, which is especially important in the case of GST isoenzyme analyses. [source] Quantitation of oxcarbazepine and its metabolites in human plasma by micellar electrokinetic chromatographyBIOMEDICAL CHROMATOGRAPHY, Issue 4 2003Vincenzo Pucci Abstract A reliable micellar electrokinetic chromatographic method for the determination of oxcarbazepine and its two main metabolites, 10-hydroxycarbamazepine and 10,11- trans -dihydroxy-10,11-dihydroxycarbamazepine, in human plasma was developed. The separation and determination of the analytes was achieved using a system consisting of 60,mM SDS in phosphate buffer (30,mM, pH 8.0), to which 20% (v/v) methanol was added. Separation was carried out in an uncoated fused-silica capillary with a separation voltage of 25,kV and currents typically less than 40,µA. Spectrophotometric detection was at 205,nm. Isolation of oxcarbazepine and its metabolites from plasma was accomplished by a solid-phase extraction procedure. The mean extraction yield of the analytes from plasma was higher than 94%. The linear correlation coefficients were better than 0.994 for all analytes. The limit of detection was 0.05,µg/mL, the limit of quantitation 0.15,µg/mL. The repeatability for the spiked blank plasma samples was lower than 1.9% and the intermediate precision lower than 2.1%, both expressed as RSD%. The results obtained analysing real plasma samples from epileptic patients under therapy with Tolep® were satisfactory in terms of precision, accuracy and detectability. Copyright© 2003 John Wiley & Sons, Ltd. [source] Determination of Bioactive Components in Polygonum perfoliatum L. by Capillary Electrophoresis with Electrochemical DetectionCHINESE JOURNAL OF CHEMISTRY, Issue 4 2009Shuping JIN Abstract The major bioactive components in a Chinese herb named Polygonum perfoliatum L. including ferulic acid, vanillic acid, quercetin, caffeic acid and protocatechuic acid were simultaneously determined by capillary electrophoresis with electrochemical detection (CE-ED) in this paper. The effects of working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CE-ED were investigated. Under the optimum conditions, the five analytes could be separated within 17 min at a separation voltage of 18 kV in 10 mmol· L,1 phosphate buffer (pH 9.2). A 300 µm diameter carbon disk electrode generated good responses at +0.95 V (vs. SCE) to the five analytes. The response was linear over three orders of magnitude with detection limits (S/N=3) ranging from 7.1×10,8 to 9.3×10,8 g·mL,1 for the analytes. This proposed method could be successfully applied to the analysis of the real samples with relatively simple extraction procedures and satisfactory results. [source] Analysis of Trace Ingredients in Green Tea by Capillary Electrophoresis with Amperometric DetectionCHINESE JOURNAL OF CHEMISTRY, Issue 3 2008Ping LI Abstract In this paper, four trace ingredients (rutin, gallic acid, quercetin, chlorogenic acid) in green tea were simultaneously determined by capillary electrophoresis coupled with amperometric detection (CE-AD). Effects of several important factors such as the pH and concentration of running buffer, separation voltage, injection time and detection potential were investigated to acquire the optimum conditions. Under the optimum conditions, the analytes could be separated within 20 min at a separation voltage of 18 kV in a 60 mmol/L borate buffer (pH 8.7). A 300 µm diameter carbon disk electrode generated good responses at 950 mV (vs. SCE) for all analytes. The relationship between the peak currents and concentrations of the analytes was linear over about three orders of magnitude with detection limits (S/N=3) ranging from 1.0×10,7 to 1.0×10,4 g·mL,1 for all the analytes. This proposed method demonstrated long-term stability and reproducibility with relative standard deviations less than 3% for both migration time and peak current (n=7), which could be successfully used for the determination of the analytes in green tea with satisfactory assay results. [source] Fast Determination of Clenbuterol and Salbutamol in Feed and Meat Products Based on Miniaturized Capillary Electrophoresis with Amperometric DetectionCHINESE JOURNAL OF CHEMISTRY, Issue 12 2007Qing-Cui CHU Abstract The fast separation capability of a novel miniaturized capillary electrophoresis with an amperometric detection (,CE-AD) system was demonstrated by determining clenbuterol and salbutamol in real samples. The effects of several factors such as the acidity and concentration of the running buffer, the separation voltage, the applied potential and the injection time on CE-AD were examined and optimized. Under the optimum conditions, the two , -agonists could be baseline separated within 60 s at a separation voltage of 2 kV in a 90 mmol/L H3BO3 -Na2B4O7 running buffer (pH 7.4), which was not interfered by ascorbic acid and uric acid. Highly linear response was obtained for above compounds over three orders of magnitude with detection limits ranging from 1.20×10,7 to 6.50×10,8 mol/L (S/N=3). This method was successfully used in the analysis of feed and meat products with relatively simple extraction procedures. [source] | ||||||||||