Home About us Contact
|
Home About us Contact | ||
|
|
||
Electrochemical Detector (electrochemical + detector)
Selected AbstractsEffects of heterogeneous electron-transfer rate on the resolution of electrophoretic separations based on microfluidics with end-column electrochemical detectionELECTROPHORESIS, Issue 19 2009Joseph Wang Abstract We demonstrate here that the electrode kinetics of an electrochemical detector contributes greatly to the resolution of the analyte bands in microchip electrophoresis systems with amperometric detection. The separation performance in terms of resolution and theoretical plate number can be improved and tailored by selecting or modifying the working electrode and/or by controlling the detection potential. Such improvements in the separation performance reflect the influence of the heterogeneous electron-transfer rate of electroactive analytes upon the post-channel band broadening, as illustrated for catechol and hydrazine compounds. The electrode kinetics thus has a profound effect not only on the sensitivity of electrochemical detectors but on the separation efficiency and the overall performance of microchip electrochemistry systems. [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] Microchip electrophoresis with wall-jet electrochemical detector: Influence of detection potential upon resolution of solutesELECTROPHORESIS, Issue 24 2006Martin Pumera Dr. Abstract This report studies the electrochemical response of wall-jet detector for microchip electrophoresis (µCE). It shows that in wall-jet configuration, the electrochemical detector operates in coulometric mode and that there is an influence of detection potential upon peak width and therefore upon the resolution of solutes. Upon raising the detection potential from +0.3 to +0.9,V, the resolution between model analytes, dopamine and catechol, increases from 0.63 to 2.90. The reasons for this behavior originate in wall-jet detector design and in its typically significant higher detector volume than the volume of injected sample. The conversion efficiency of the wall-jet electrochemical detection cell was found to be 97.4% for dopamine and 98.0% for catechol. The paper brings deeper understanding of operations of wall-jet electrochemical detectors for microchip devices, and it explains previously reported significantly sharper peaks when electrocatalytic electrodes (i.e., palladium and carbon nanotube) were used in µCE-electrochemistry wall-jet detector. [source] Direct electrochemical detection of glucose in human plasma on capillary electrophoresis microchipsELECTROPHORESIS, Issue 21-22 2004Yan Du Abstract We developed an electrochemical detector on a hybrid chip for the determination of glucose in human plasma. The microchip system described in this paper consists of a poly(dimethylsiloxane) (PDMS) layer containing separation and injection channels and an electrode plate. The copper microelectrode is fabricated by selective electroless deposition. The fabrication of the decoupler is performed by platinum electrochemical deposition on the metal film formed by electroless deposition. Factors influencing the performance, including detection potential, separation field strength, and buffer concentration, were studied. The electrodes exhibited good stability and durability in the analytical procedures. Under optimized detection conditions, glucose responded linearly from 10 ,M to 1 mM. Finally, glucose in human plasma from three healthy individuals and two diabetics was successfully determined, giving a good prospect for a new clinical diagnostic instrument. [source] Oxidative DNA damage in gastric cancer: CagA status and OGG1 gene polymorphismINTERNATIONAL JOURNAL OF CANCER, Issue 1 2008Fabio Farinati Abstract Oxidative DNA damage is thought to play an important part in the pathogenesis of H. pylori -induced mucosal damage. 8-OHdG is a sensitive marker of DNA oxidation and is repaired by a polymorphic glycosylase (OGG1) more effectively than by OGG1 -Cys326. The aims of this study were to ascertain the respective roles of H. pylori, cagA status and OGG1 polymorphism in determining 8-OHdG levels in benign and premalignant stomach diseases and in gastric cancer (GC). The study involved 50 GC patients (for whom both neoplastic tissue and surrounding mucosa were available), 35 with intestinal metaplasia and atrophy (IMA) and 43 controls. H. pylori and cagA status were determined by histology and polymerase chain reaction for urease and cagA. 8-OHdG was assayed using HPLC with an electrochemical detector (HPLC-ED). The OGG1 1245C,G transversion was identified using RFLP analyses. 8-OHdG levels were significantly higher in GC, with no differences in relation to H. pylori or cagA status. OGG1 polymorphism was documented in 34% of GC (15 Ser/Cys, 2 Cys/Cys). OGG1 1245C,G polymorphism was detected in 54% of IMA patients, but only 16% of controls (p = 0.0004) and coincided with significantly higher 8-OHdG levels. In the multivariate analysis, 8-OHdG levels were predicted by histotype and OGG1 status. OGG1 1245C,G polymorphism was common in both GC and IMA, but very rare in controls, and correlated more closely with 8-OHdG levels than do H. pylori infection or cagA status. © 2008 Wiley-Liss, Inc. [source] A comparison of changes in the transformation of isoflavones in soymilk using varying concentrations of exogenous and probiotic-derived endogenous , -glucosidasesJOURNAL OF APPLIED MICROBIOLOGY, Issue 3 2007D.O. Otieno Abstract Aims:, To compare endogenous and exogenous , -glucosidases for the hydrolysis of the predominant isoflavone glucosides in soymilk in order to improve the biological activity. Methods and Results:,, -glucosidase activity of probiotic organisms, including Bifidobacterium animalis ssp. lactis Bb12, Lactobacillus acidophilus ATCC 4461 and Lactobacillus casei 2607 in soymilk, was evaluated and was related to the increase in the concentration of isoflavone aglycones during fermentation. The concentrations of isoflavone compounds in soymilk were monitored using a Varian model HPLC with an Amperometric electrochemical detector. The aglycone composition, also known as aglycone equivalent ratio, has been considered to be important for the delivery of health benefits of isoflavones, and was monitored during the fermentation of soymilk. Comparison of the hydrolytic effectiveness of both exogenous and endogenous enzyme during 4-h incubation in soymilk was conducted using the Otieno,Shah (O,S) index. Results showed that exogenous enzyme exhibited faster rate of isoflavone glucoside hydrolysis than that by endogenous enzyme. Highest O,S indices were obtained after 4, 3 and 2 h of incubation with enzyme solution having , -glucosidase activity of 0·288 U ml,1, 0·359 U ml,1 and 0·575 U ml,1, resulting into aglycone concentration increments of 5·87-, 6·07- and 5·94-fold, respectively. Conversely, aglycone concentration in the soymilk with B. animalis ssp. lactis Bb12, L. casei 2607 and L. acidophilus 4461 increased by 3·43-, 2·72- and 3·03-fold, respectively, after 4 h of fermentation at 37°C. In addition, the O,S index of endogenous enzyme was much lower than that of the exogenous enzyme over the same 4-h incubation period. Optimum aglycone equivalent ratios coincided with highest O,S indices and highest aglycone concentrations in soymilk hydrolysed with exogenous enzyme. The same correlation of O,S indices and highest aglycone concentrations occurred for endogenous enzyme during the 24 h of fermentation. Conclusions:, Obtaining highest aglycone concentration and optimum aglycone equivalent ratio could provide a critical beginning point in clinical trials for the realization of unique health benefits of soy isoflavones. Significance and Impact of the Study:, Screening for , -glucosidase activities of probiotics in soymilk and comparing their hydrolytic potentials with that of exogenous , -glucosidase could find wide applications in the development of different aglycone-rich functional soy beverages. [source] Simultaneous determination of BNP7787 and its metabolite mesna in plasma and tissue by micro-HPLC with a dual electrochemical detectorJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2003Miranda Verschraagen Abstract Sensitive, accurate, and precise assays are described to determine BNP7787 (disodium 2,2,-dithio-bis-ethane sulfonate) and its metabolite mesna (sodium 2-mercaptoethane sulfonate) simultaneously in plasma and tissue by micro-high-performance liquid chromatography (HPLC) with dual electrochemical detection. After separation of BNP7787 and mesna by micro-HPLC, the disulfide BNP7787 was reduced to mesna by a reactor cell with a glassy carbon working electrode (,1.6 V versus Hy-REF). At the second electrode, which consisted of a gold wall-jet electrode, the mesna generated from BNP7787 and the mesna already present in the samples were detected (+0.85 V versus Ag/AgCl). The lower limit of quantification (LLQ) of both compounds was 3 ,M in plasma and 20 nmol/g in tissue. The dynamic range of the assay in plasma was 3,120 ,M for mesna and 15,1200 ,M for BNP7787. In tissue, the dynamic range was 20,2000 nmol/g for both compounds. The recovery of mesna from plasma and tissue ranged from 61.4 to 90.5% and 82.7 to 90.2%, respectively, and seemed to be concentration dependent. The recovery of BNP7787 from plasma and tissue was complete (i.e., 101.5 and 96.4%, respectively). The within- and between-day accuracy and precision for the plasma and tissue assay were within 14 and 7%, respectively. The utility of the assay was shown by determination of the stability of mesna and BNP7787 in a kidney sample of a rat and by analysis of plasma samples obtained from a patient receiving 18.4 g/m2 BNP7787 as a 15-min intravenous infusion. © 2003 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 92:1040,1050, 2003 [source] HPLC for stress-free screening of potential prostate cancer marker catechol estrogens in urine using a diamond-electrode electrochemical and a fluorescence detectorJOURNAL OF SEPARATION SCIENCE, JSS, Issue 14 2007Masatoki Katayama Abstract Improvement of the sensitivity and specificity of a simultaneous stress-free screening method for catechol estrogens as a potential prostate cancer marker in urine has been accomplished by HPLC with a diamond-electrode electrochemical detector and a fluorescence detector. Since taking urine samples generates less stress (or pain) than the drawing of blood, the method can readily be applied to almost any patient, and will also assist in improving the sensitivity and specificity of the prostatic specific antigen test. Catechol estrogens (2-hydroxyestrone, 4-hydroxyestrone, 2-methoxyestrone, 2-hydroxyestradiol, 4-hydroxyestradiol, 2-methoxyestradiol, and 2-hydroxyestriol) and estrogens (estrone, estradiol, estriol) were separated on an Inertsil ODS-II column with acetonitrile,potassium dihydrogen phosphate (pH 3.0). The diamond-electrode electrochemical detector used had the great advantage of being a maintenance-free system, and could sequentially analyze hundreds of samples. Fluorescence detection improved the sensitivity 10,500 times (e. g., the LOD of 2-hydroxyestriol was improved 250 times) compared to previous electrochemical detection reports, and dual detection improved peak identification in the urine samples. The proposed method was applied to the simultaneous determination of catechol estrogens in spiked urine in a preliminary study on estrogens and PSA values in biopsy and prostate cancer patients. [source] Oxidative DNA Damage Induced by a Metabolite of 2,Naphthylamine, a Smoking-related Bladder CarcinogenCANCER SCIENCE, Issue 7 2002Shiho Ohnishi 2-Naphthylamine (2-NA), a bladder carcinogen, is contained in cigarette smoke. DNA adduct formation is thought to be a major cause of DNA damage by carcinogenic aromatic amines. We have investigated whether a metabolite of 2-NA, 2-nitroso-1-naphthol (NO-naphthol) causes oxidative DNA damage, using 32P-labeled DNA fragments. We compared the mechanism of DNA damage induced by NO-naphthol with that by N -hydroxy-4-aminobiphenyl (4-ABP (NHOH)), a metabolite of 4-aminobiphenyl, another smoking-related bladder carcinogen. NO-naphthol caused Cu(II)-mediated DNA damage at T>C>G residues, with non-enzymatic reduction by NADH. Catalase and bathocuproine, a Cu(I)-specific chelator, inhibited the DNA damage, suggesting the involvement of H2O2 and Cu(I). Some free ·OH scavengers also attenuated NO-naphthol-induced DNA damage, while free ·OH scavengers had no effect on the DNA damage induced by 4,ABP(NHOH). This difference suggests that the reactive species formed by NO-naphthol has more free ·OH- character than that by 4,ABP(NHOH). A high-pressure liquid chromatograph equipped with an electrochemical detector showed that NO-naphthol induced 8,oxo,7,8,dihydro,2,,deoxyguanosine formation in the presence of NADH and Cu(II). The oxidative DNA damage by these aminoaromatic compounds may participate in smoking-related bladder cancer, in addition to DNA adduct formation. [source] Life Style and Urinary 8-Hydroxydeoxyguanosine, a Marker of Oxidative DNA Damage: Effects of Exercise, Working Conditions, Meat Intake, Body Mass Index, and SmokingCANCER SCIENCE, Issue 1 2001Hiroshi Kasai The urinary levels of 8-hydroxydeoxyguanosine (8-OH-dG), a marker of oxidative DNA damage, of 318 healthy men aged 18-58 were measured with high resolution by a newly developed automated high-pressure liquid chromatography (HPLC) system coupled to an electrochemical detector (ECD). The mean 8-OH-dG level (,Mg/g creatinine) was 4.12±1.73 (SD). An eleven-fold inter-individual variation was observed. The accuracy of the measurement estimated from the recovery of an added 8-OH-dG standard was 90-98%. By univariate analysis, it was found that moderate physical exercise (P=0.0023) and high body mass index (BMI) (P=0.0032) reduced the 8-OH-dG level, while physical labor (P=0.0097), smoking (P=0.032), and low meat intake (less than once/ week) (P=0.041) increased its level. Based on a multi-regression analysis of the log-transformed values, moderate physical exercise (P=0.0039), high BMI (P=0.0099), and age (P=0.021) showed significant reducing effects on the 8-OH-dG level, while low meat intake (P=0.010), smoking (P=0.013), and day-night shift work (P=0.044) increased its level. These results suggest that many types of life-style factors that either generate or scavenge oxygen radicals may affect the level of oxidative DNA damage of each individual. [source] Real-Time Monitoring of Mass-Transport-Related Enzymatic Reaction Kinetics in a Nanochannel-Array ReactorCHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2010Su-Juan Li Abstract To understand the fundamentals of enzymatic reactions confined in micro-/nanosystems, the construction of a small enzyme reactor coupled with an integrated real-time detection system for monitoring the kinetic information is a significant challenge. Nano-enzyme array reactors were fabricated by covalently linking enzymes to the inner channels of a porous anodic alumina (PAA) membrane. The mechanical stability of this nanodevice enables us to integrate an electrochemical detector for the real-time monitoring of the formation of the enzyme reaction product by sputtering a thin Pt film on one side of the PAA membrane. Because the enzymatic reaction is confined in a limited nanospace, the mass transport of the substrate would influence the reaction kinetics considerably. Therefore, the oxidation of glucose by dissolved oxygen catalyzed by immobilized glucose oxidase was used as a model to investigate the mass-transport-related enzymatic reaction kinetics in confined nanospaces. The activity and stability of the enzyme immobilized in the nanochannels was enhanced. In this nano-enzyme reactor, the enzymatic reaction was controlled by mass transport if the flux was low. With an increase in the flux (e.g., >50,,L,min,1), the enzymatic reaction kinetics became the rate-determining step. This change resulted in the decrease in the conversion efficiency of the nano-enzyme reactor and the apparent Michaelis,Menten constant with an increase in substrate flux. This nanodevice integrated with an electrochemical detector could help to understand the fundamentals of enzymatic reactions confined in nanospaces and provide a platform for the design of highly efficient enzyme reactors. In addition, we believe that such nanodevices will find widespread applications in biosensing, drug screening, and biochemical synthesis. [source] Electrochemical Sensing of ExplosivesELECTROANALYSIS, Issue 4 2007Joseph Wang Abstract This article reviews recent advances in electrochemical sensing and detection of explosive substances. Escalating threats of terrorist activities and growing environmental concerns have generated major demands for innovative field-deployable tools for detecting explosives in a fast, sensitive, reliable and simple manner. Field detection of explosive substances requires that a powerful analytical performance be coupled to miniaturized low-cost instrumentation. Electrochemical devices offer attractive opportunities for addressing the growing explosive sensing needs. The advantages of electrochemical systems include high sensitivity and selectivity, speed, a wide linear range, compatibility with modern microfabrication techniques, minimal space and power requirements, and low-cost instrumentation. The inherent electroactivity of nitroaromatic, nitramine and nitroester compounds makes them ideal candidates for electrochemical detection. Recent activity in various laboratories has led to the development of disposable sensor strips, novel electrode materials, submersible remote sensors, and electrochemical detectors for microchip (,Lab-on-Chip') devices for on-site electrochemical detection of explosive substances. The attractive behavior of these electrochemical monitoring systems makes them very promising for addressing major security and environmental problems. [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] Effects of heterogeneous electron-transfer rate on the resolution of electrophoretic separations based on microfluidics with end-column electrochemical detectionELECTROPHORESIS, Issue 19 2009Joseph Wang Abstract We demonstrate here that the electrode kinetics of an electrochemical detector contributes greatly to the resolution of the analyte bands in microchip electrophoresis systems with amperometric detection. The separation performance in terms of resolution and theoretical plate number can be improved and tailored by selecting or modifying the working electrode and/or by controlling the detection potential. Such improvements in the separation performance reflect the influence of the heterogeneous electron-transfer rate of electroactive analytes upon the post-channel band broadening, as illustrated for catechol and hydrazine compounds. The electrode kinetics thus has a profound effect not only on the sensitivity of electrochemical detectors but on the separation efficiency and the overall performance of microchip electrochemistry systems. [source] Microchip electrophoresis with wall-jet electrochemical detector: Influence of detection potential upon resolution of solutesELECTROPHORESIS, Issue 24 2006Martin Pumera Dr. Abstract This report studies the electrochemical response of wall-jet detector for microchip electrophoresis (µCE). It shows that in wall-jet configuration, the electrochemical detector operates in coulometric mode and that there is an influence of detection potential upon peak width and therefore upon the resolution of solutes. Upon raising the detection potential from +0.3 to +0.9,V, the resolution between model analytes, dopamine and catechol, increases from 0.63 to 2.90. The reasons for this behavior originate in wall-jet detector design and in its typically significant higher detector volume than the volume of injected sample. The conversion efficiency of the wall-jet electrochemical detection cell was found to be 97.4% for dopamine and 98.0% for catechol. The paper brings deeper understanding of operations of wall-jet electrochemical detectors for microchip devices, and it explains previously reported significantly sharper peaks when electrocatalytic electrodes (i.e., palladium and carbon nanotube) were used in µCE-electrochemistry wall-jet detector. [source] | ||||||||||||||||