Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Detector

  • area detector
  • array detector
  • ccd detector
  • conductivity detector
  • diode array detector
  • diode-array detector
  • edge detector
  • electrochemical detector
  • evaporative light scattering detector
  • flame ionization detector
  • fluorescence detector
  • imaging-plate detector
  • ionization detector
  • light scattering detector
  • multiuser detector
  • photodiode array detector
  • pixel detector
  • position-sensitive detector
  • radiation detector
  • scattering detector
  • selective detector
  • uv detector
  • x-ray detector

  • Terms modified by Detector

  • detector set
  • detector system

  • Selected Abstracts

    Characterization and Assessment of the Microjet Electrode as a Detector for HPLC

    ELECTROANALYSIS, Issue 9 2004
    Susan Cannan
    Abstract The microjet electrode (MJE) is characterized as a detector for high performance liquid chromatography (HPLC). Voltammetric measurements of the oxidation of hydroquinone (HQ) allow mass transport to be determined for the MJE detector configuration, and the factors controlling the conversion efficiency of the device to be well understood. The current-time response to the flow injection analysis of volumes of solution in the 10,80,,L range has been established, and the limit of detection of this method has been determined. The latter was found to approach that of UV absorbance measurements, which is particularly encouraging, given that HQ has a relatively strong chromophore (,=2,290.8,cm,1 mol,1,L). This detection system is a robust and simple arrangement with the capability of analyzing large volumes of eluent at typical analytical HPLC flow rates. [source]

    Accuracy of computer-automated caries detection in digital radiographs compared with human observers

    Ann Wenzel
    The aim of this study was to compare diagnostic accuracy of a caries detection program with that of human observers. A total of 190 extracted teeth were radiographed with two Trophy RVG (RadioVisioGraphy) digital sensor systems. Four observers scored the approximal surfaces in all images on a disease severity scale. Each observer thereafter used the Logicon Caries Detector (LCD) program to analyse the surfaces in the digital images and recorded their outcome. To determine the true absence or presence of caries, histological validation was used. Sensitivities, specificities, positive and negative predictive values were calculated and differences between the diagnostic methods tested. Specificities for the outcome with the LCD were significantly lower for three observers than when they themselves assessed the RVG images and, correspondingly, the positive predictive values were lower for the LCD outcome for three of the observers. Sensitivity was also lower for two observers on the diagnostic threshold caries in dentine. It was concluded that the automated caries detection program is less accurate than human observers in detecting approximal caries lesions. [source]

    Chemical Agent Simulant Release from Clothing Following Vapor Exposure

    Robert J. Feldman MD
    ACADEMIC EMERGENCY MEDICINE 2010; 17:1,4 © 2010 by the Society for Academic Emergency Medicine Abstract Objectives:, Most ambulatory victims of a terrorist chemical attack will have exposure to vapor only. The study objective was to measure the duration of chemical vapor release from various types of clothing. Methods:, A chemical agent was simulated using methyl salicylate (MeS), which has similar physical properties to sulfur mustard and was the agent used in the U.S. Army's Man-In-Simulant Test (MIST). Vapor concentration was measured with a Smiths Detection Advanced Portable Detector (APD)-2000 unit. The clothing items were exposed to vapor for 1 hour in a sealed cabinet; vapor concentration was measured at the start and end of each exposure. Clothing was then removed and assessed every 5 minutes with the APD-2000, using a uniform sweep pattern, until readings remained 0. Results:, Concentration and duration of vapor release from clothing varied with clothing composition and construction. Lightweight cotton shirts and jeans had the least trapped vapor; down outerwear, the most. Vapor concentration near the clothing often increased for several minutes after the clothing was removed from the contaminated environment. Compression of thick outerwear released additional vapor. Mean times to reach 0 ranged from 7 minutes for jeans to 42 minutes for down jackets. Conclusions:, This simulation model of chemical vapor release demonstrates persistent presence of simulant vapor over time. This implies that chemical vapor may be released from the victims' clothing after they are evacuated from the site of exposure, resulting in additional exposure of victims and emergency responders. Insulated outerwear can release additional vapor when handled. If a patient has just moved to a vapor screening point, immediate assessment before additional vapor can be released from the clothing can lead to a false-negative assessment of contamination. [source]

    Controlled Growth of High-Quality ZnO-Based Films and Fabrication of Visible-Blind and Solar-Blind Ultra-Violet Detectors

    ADVANCED MATERIALS, Issue 45 2009
    Xiaolong Du
    Abstract ZnO is a wide-bandgap (3.37,eV at room temperature) oxide semiconductor that is attractive for its great potential in short-wavelength optoelectronic devices, in which high quality films and heterostructures are essential for high performance. In this study, controlled growth of ZnO-based thin films and heterostructures by molecular beam epitaxy (MBE) is demonstrated on different substrates with emphasis on interface engineering. It is revealed that ultrathin AlN or MgO interfacial layers play a key role in establishing structural and chemical compatibility between ZnO and substrates. Furthermore, a quasi-homo buffer is introduced prior to growth of a wurtzite MgZnO epilayer to suppress the phase segregation of rock-salt MgO, achieving wide-range bandgap tuning from 3.3 to 4.55,eV. Finally, a visible-blind UV detector exploiting a double heterojunction of n-ZnO/insulator-MgO/p-Si and a solar-blind UV detector using MgZnO as an active layer are fabricated by using the growth techniques discussed here. [source]

    Introduction to the Special Issue on Detectors

    Heinz Graafsma
    First page of article [source]

    Workshop on X-ray Detectors for Synchrotron Radiation

    DOI: 10.1107/S090904950400926
    First page of article [source]

    Application of fast-digitizer card Acqiris DP-240 in positron lifetime spectroscopy

    Martin Petriska
    Abstract Based on the available knowledge base in positron annihilation measurements, new software for digital positron lifetime spectrometry has been designed within the frame of joint activity between STU Bratislava and JRC Petten. The tests of the new positron digital-life time setup have been carried out. Detectors with BaF2 scintillators and fast-dynode outputs were chosen for such studies. As the digitiser unit, the card Acqiris DP240 was fully tested. Originally, start and stop timing signals were sampled to digital waveforms separately at a rate of 1 GS/s in 8 bit resolution. However, due to limited quality of collected waveforms which significantly affected post-processing of data, the joined delayed channel mode with 2 GS/s sampling rate was applied for further studies. The full setup was benchmarked by a series of calibration measurements of two high purity materials, specifically Si and Ni. The inter-comparison of conventional analogue- and digital-based processing are discussed in detail. Further, the optimisation of main parameters for waveform-processing are analysed too. Such a new approach in the digital life-time spectroscopy will help to improve the resolution of existing methodology which might enhance the capabilities of this technique for further applications, especially in materials science. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    3D Image Segmentation of Aggregates from Laser Profiling

    Hyoungkwan Kim
    Automated scanners of different designs use cameras or lasers to obtain digital images of groups of aggregate particles. To accurately determine particle size and shape parameters, each particle region in the image must be isolated and processed individually. Here, a method for segmenting a particle image acquired from laser profiling is developed using a Canny edge detector and a watershed transformation. Canny edges with rigorous and liberal threshold values are used to outline particle boundaries on a binary image and to check the validity of watersheds, respectively. To find appropriate regional minima in the watershed transformation, a varying search window method is used, where the number of neighboring pixels being compared with the pixel of interest is determined from the height value of the pixel. Test results with this method are promising. When implemented in automated systems that are designed to rapidly assess size and shape characteristics of stone particles, this technique can not only reduce the amount of time required for aggregate preparation, but also increase the accuracy of analysis results. [source]

    The Neutralizer: a self-configurable failure detector for minimizing distributed storage maintenance cost

    Zhi Yang
    Abstract To achieve high data availability or reliability in an efficient manner, distributed storage systems must detect whether an observed node failure is permanent or transient, and if necessary, generate replicas to restore the desired level of replication. Given the unpredictability of network dynamics, however, distinguishing permanent and transient failures is extremely difficult. Though timeout-based detectors can be used to avoid mistaking transient failures as permanent failures, it is unknown how the timeout values should be selected to achieve a better tradeoff between detection latency and accuracy. In this paper, we address this fundamental tradeoff from several perspectives. First, we explore the impact of different timeout values on maintenance cost by examining the probability of their false positives and false negatives. Second, we propose a self-configurable failure detector called the Neutralizer based on the idea of counteracting false positives with false negatives. The Neutralizer could enable the system to maintain a desired replication level on average with the least amount of bandwidth. We conduct extensive simulations using real trace data from a widely deployed peer-to-peer system and synthetic traces based on PlanetLab and Microsoft PCs, showing a significant reduction in aggregate bandwidth usage after applying the Neutralizer (especially in an environment with a low average node availability). Overall, we demonstrate that the Neutralizer closely approximates the performance of a perfect ,oracle' detector in many cases. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Purification and crystal growth of TlBr for application as a radiation detector

    I. B. Oliveira
    Abstract Thallium bromide is a semiconductor compound with high atomic number and density. It has a CsCl-type simple cubic crystal structure and it is non-hygroscopics. The TlBr crystals are relatively soft with a knoop hardness number of 12. In this work, the TlBr commercial powder was purified by zone refining and the purest material section was used for crystal growth by Bridgman method. Efforts have been concentrated on the purification of the TlBr. The purification efficiency has been evaluated (NAA and ICP-MS) by impurities reduction results after zone refining passes. The crystalline quality was evaluated by X-ray diffraction. The characterized TlBr crystal as a detector has shown good response to gamma radiation. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Double Modification of Electrode Surface for the Selective Detection of Epinephrine and Its Application to Flow Injection Amperometric Analysis

    ELECTROANALYSIS, Issue 22 2009
    Guang-Ri Xu
    Abstract A glassy carbon electrode having two polymer layers has been applied to selectively detect epinephrine. The inner layer formed by electropolymerization of macrocyclic nickel complex functioned as an electrocatalyst for epinephrine oxidation and the outer layer composed of hydrolyzed polyurethane ,-benzyl L -glutamate as a screening layer. Differential pulse voltammetry showed almost 100% recovery of epinephrine even in 100-fold excess of interferents. When applied to a dual glassy carbon electrode as an amperometric detector in flow injection analysis, a linear response over 0.1,,M and 10,,M was obtained. Recovery tested for 5-fold diluted human urine samples was 97.5%. [source]

    The Dependence of the Sensitivity and Reliability of Contactless Conductivity Detection on the Wall Thickness of Electrophoretic Fused-Silica Capillaries

    ELECTROANALYSIS, Issue 3-5 2009
    Petr T
    Abstract A contactless conductivity detector (C4D) performance has been tested on a simple capillary electrophoretic separation in a standard fused-silica capillary with an external diameter of 360,,m and in a thin-walled capillary (an external diameter of 150,,m); the internal diameters of the two capillaries were identical, equal to 75,,m. Potassium and sodium ions have been separated in a morpholinoethanesulfonic acid/histidine background electrolyte (MES/His), over a wide range of its concentrations (0,100,mM). At low MES/His concentrations, the C4D response, obtained from the height of the potassium peak, is by 100 to 200 per cent higher for the thin-walled capillary and the calibration dependences are linear, in contrast to the thick-walled capillary. These differences between the two capillaries decrease with increasing MES/His concentration, the C4D response in the thin-walled capillary is then higher by mere 20 per cent and the calibration dependences are linear in both the capillaries. The highest sensitivities have been obtained at a MES/His concentration of 50,mM, with LOD values for potassium ion of 2.0 and 2.6,,M, in the thin- and thick-walled capillaries, respectively. The signal-to-noise ratios and the plate counts are generally similar for the two capillaries. It follows from the results that special thin-walled capillaries can be advantageous when background electrolytes with very low conductivities must be employed. [source]

    Development of a Novel Automatic Potentiometric System for Determination of Selenium and Its Application in Pharmaceutical Formulations and Anodic Slime

    ELECTROANALYSIS, Issue 9 2008
    Abstract Poly(vinyl chloride) polymeric membrane sensors containing Sn(IV) phthalocyanine dichloride (SnPC) and Co(II) phthalocyanine (CoPC) as novel electroactive materials dispersed in o -nitrophenyl octylether (o -NPOE) as a plasticizer are examined potentiometrically with respect to their response toward selenite (SeO32,) ions. Fast Nernstian response for SeO32, ions over the concentration ranges 7.0×10,6,1.0×10,3 and 8.0×10,6,1.0×10,3 mol L,l at pH,3.5,8.5 with lower detection limit of 5.0×10,6 and 8.0×10,6 mol L,1 and calibration slopes of ,25.4 and ,29.7,mV decade,1 are obtained with SnPC and CoPC based membrane sensors, respectively. The proposed sensors reveals by the modified separate solution method (MSSM) a good selectivity over different anions which differ significantly from the classical Hofmeister series. A segmented sandwich membrane method is used to determine complex formation constants of the ionophores in situe in the solvent polymeric sensing membranes. Membrane incorporating CoPC in a tubular flow detector is used in a two channels flow injection set up for continuous monitoring of selenite at a frequency of ca. 50 samples h,1. Direct determination of selenium in pharmaceutical formulations and anodic slime gives results in good agreement with data obtained using standard ICP method. [source]

    Amperometric Biosensors Based on Choline Oxidase Entrapped in Polyacrylamide Microgels

    ELECTROANALYSIS, Issue 2-3 2007
    López, M. Sánchez-Paniagua
    Abstract A choline amperometric biosensor has been designed using as biological component choline oxidase (ChOx) entrapped in polyacrylamide microgels. The working electrode was prepared by holding the enzyme loaded microgels on a platinum electrode by a dialysis membrane. It was found that the optimum microgel cross-linking required to retain ChOx and to allow the diffusion of choline was 7.0%. The response of the biosensor was optimized in relation to pH, temperature and working potential and the following optimal values were obtained: pH,9.0, temperature range between 20 and 30,°C, and potential +0.6,V. Under optimal conditions the sensitivity for choline was 17.45,mA M,1 cm,2, the detection limit 8,,M, and the response linear range from 2×10,5 M to 2×10,4 M. This biosensor has been also used as a nicotine detector due to the inhibition of the catalytic activity of choline oxidase by this compound. Moreover, the simultaneous entrapment of a second enzyme, acetylcholinesterase (AChE), in the microgels makes the biosensor sensible to acetylcholine. [source]

    Electrocatalytic Oxidation of Sulfur Containing Amino Acids at Renewable Ni-Powder Doped Carbon Ceramic Electrode: Application to Amperometric Detection L -Cystine, L -Cysteine and L -Methionine

    ELECTROANALYSIS, Issue 21 2006
    Abdollah Salimi
    Abstract A sol-gel technique was used here to prepare a renewable carbon ceramic electrode modified with nickel powder. Cyclic voltammograms of the resulting modified electrode show stable and a well defined redox couple due to Ni(II)/Ni(III) system with surface confined characteristics. The modified electrode shows excellent catalytic activity toward L -cystine, L -cysteine and L -methionine oxidation at reduced overpotential in alkaline solutions. In addition the antifouling properties at the modified electrode toward the above analytes and their oxidation products increases the reproducibility of results. L -cystine, L -cysteine and L -methionine were determined chronoamperometricaly at the surface of this modified electrode at pH range 9,13. Under the optimized conditions the calibration curves are linear in the concentration range 1,450,,M, 2,90,,M and 0.2,75,,M for L -cystine, L -methionine and L -cysteine determination, respectively. The detection limit and sensitivity were 0.64,,M, 3.8,nA/ ,M for L -cystine, 2,,M, 5.6,nA/ ,M for L -methionine and 0.2,,M and 8.1,nA/,M for L -cysteine. The advantageous of this modified electrode is high response, good stability and reproducibility, excellent catalytic activity for oxidation inert molecules at reduced overpotential and possibility of regeneration of the electrode surface by potential cycling for 5,minutes. Furthermore, the modified electrode has been prepared without using specific reagents. This sensor can be used as an amperometric detector for disulfides detection in chromatographic or flow systems. [source]

    A LiMn2O4 Based Electrochemical Scheme for Selective Measurement of Dopamine

    ELECTROANALYSIS, Issue 3 2006
    Hoang, Jyh Leu
    Abstract A new cathodic scheme was developed for the determination of dopamine by flow injection analysis (FIA). A mild oxidizing agent, lithium manganese (III, IV) oxide (LiMn2O4), as an upstream modifier can oxidize the dopamine to produce the dopaminequinone, and then the oxidized product is subsequently detected by the downstream detector at ,0.1,V (vs. Ag/AgCl). In this work, the significant feature of LiMn2O4 based sensing scheme possesses no interference from other tested biological amines including acetylcholine, epinephrine, glutamate, and histamine. Otherwise, there is no detectable interference from ascorbic acid, but 2% and 1% negligible interferences were found from uric acid and acetaminophen, respectively. [source]

    Separation and Detection of Nitrophenols at Capillary Electrophoresis Microchips with Amperometric Detection

    ELECTROANALYSIS, Issue 2 2006
    Jan 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]

    Contactless Conductivity Detection in Capillary Electrophoresis: A Review

    ELECTROANALYSIS, Issue 24 2004
    Pavel Kubá
    Abstract The popularity of contactless conductivity detection in capillary electrophoresis has been growing steadily over the last few years. Improvements have been made in the design of the detector in order to facilitate its handling, to allow easy incorporation into available instruments or to achieve higher sensitivity. The understanding of its fundamental working principles has been advanced and the detection approach has also been transferred to lab-on-chip devices. The range of applications has been extended greatly from the initial work on small inorganic ions to include organic species and biomolecules. Concurrent determination of cations and anions by dual injection from opposite ends has been demonstrated as well as sample introduction by using flow-injection systems for easy automation of the process. [source]

    Characterization and Assessment of the Microjet Electrode as a Detector for HPLC

    ELECTROANALYSIS, Issue 9 2004
    Susan Cannan
    Abstract The microjet electrode (MJE) is characterized as a detector for high performance liquid chromatography (HPLC). Voltammetric measurements of the oxidation of hydroquinone (HQ) allow mass transport to be determined for the MJE detector configuration, and the factors controlling the conversion efficiency of the device to be well understood. The current-time response to the flow injection analysis of volumes of solution in the 10,80,,L range has been established, and the limit of detection of this method has been determined. The latter was found to approach that of UV absorbance measurements, which is particularly encouraging, given that HQ has a relatively strong chromophore (,=2,290.8,cm,1 mol,1,L). This detection system is a robust and simple arrangement with the capability of analyzing large volumes of eluent at typical analytical HPLC flow rates. [source]

    Determination of Reserpine in Urine by Capillary Electrophoresis with Electrochemiluminescence Detection

    ELECTROANALYSIS, Issue 3 2004
    Weidong Cao
    Abstract A fast and sensitive approach to detect reserpine in urine using micellar electrokinetic capillary chromatography with electrochemiluminescence (ECL) of Ru(bpy)32+ detection is described. Using a 25,,m i.d. capillary as separation column, the ECL detector was coupled to the capillary in the absence of an electric field decoupler. Field-amplified injection was used to minimize the effect of ionic strength in the sample and to achieve high sensitivity. In this way, the sample was analyzed directly without any pretreatment. The method was validated for reserpine in the urine over the range of 1×10,6,1×10,4,mol/L with a correlation coefficient of 0.996. The RSD for reserpine at a level of 5,,mol/L was 4.3%. The LOD (S/N=3) was estimated to be 7.0×10,8,mol/L. The average recoveries for 10,,mol/L reserpine spiked in human urine were 94%. [source]

    High-sensitivity detection of oxytetracycline using light scattering agglutination assay with aptasensor

    ELECTROPHORESIS, Issue 18 2010
    Keesung Kim
    Abstract We present an aptamer-based biosensor (aptasensor) for rapid and high-sensitive detection of oxytetracycline (OTC) antibiotic in PBS inside a Y-channel PDMS microfluidic device. The detection was made by real-time monitoring of the agglutination assay of ssDNA aptamer-conjugated polystyrene latex microspheres with proximity optical fibers. The agglutination assay was performed with serially diluted OTC antibiotic solutions using highly carboxylated polystyrene particles of 920,nm diameter conjugated with OTC-binding ssDNA aptamer. Proximity optical fibers were used to measure the increase in 45° forward light scattering of the aggregated particles by fixing them around the viewing cell of the device with stable angle and distance to the detector. The detection limit was around 100,ppb for the current aptasensor system with the detection time less than 3,min. [source]

    CEC-ESI ion trap MS of multiple drugs of abuse

    ELECTROPHORESIS, Issue 7 2010
    Zeineb Aturki
    Abstract This article describes a method for the separation and determination of nine drugs of abuse in human urine, including amphetamines, cocaine, codeine, heroin and morphine. This method was based on SPE on a strong cation exchange cartridge followed by CEC-MS. The CEC experiments were performed in fused silica capillaries (100,,m×30,cm) packed with a 3,,m cyano derivatized silica stationary phase. A laboratory-made liquid junction interface was used for CEC-MS coupling. The outlet capillary column was connected with an emitter tip that was positioned in front of the MS orifice. A stable electrospray was produced at nanoliter per minute flow rates applying a hydrostatic pressure (few kPa) to the interface. The coupling of packed CEC columns with mass spectrometer as detector, using a liquid junction interface, provided several advantages such as better sensitivity, low dead volume and independent control of the conditions used for CEC separation and ESI analysis. For this purpose, preliminary experiments were carried out in CEC-UV to optimize the proper mobile phase for CEC analysis. Good separation efficiency was achieved for almost all compounds, using a mixture containing ACN and 25,mM ammonium formate buffer at pH 3 (30:70, v/v), as mobile phase and applying a voltage of 12,kV. ESI ion-trap MS detection was performed in the positive ionization mode. A spray liquid, composed by methanol,water (80:20, v/v) and 1% formic acid, was delivered at a nano-flow rate of ,200,nL/min. Under optimized CEC-ESI-MS conditions, separation of the investigated drugs was performed within 13,min. CEC-MS and CEC-MS2 spectra were obtained by providing the unambiguous confirmation of these drugs in urine samples. Method precision was determined with RSDs values ,3.3% for retention times and ,16.3% for peak areas in both intra-day and day-to-day experiments. LODs were established between 0.78 and 3.12,ng/mL for all compounds. Linearity was satisfactory in the concentration range of interest for all compounds (r2,0.995). The developed CEC-MS method was then applied to the analysis of drugs of abuse in spiked urine samples, obtaining recovery data in the range 80,95%. [source]

    A new evaluation technique for the detection of impurities in purified proteins via CE with native UV-LIF

    ELECTROPHORESIS, Issue 2 2010
    Audrey Rodat
    Abstract An analytical methodology for quality control analyses of IgG and their impurities is presented using a new UV-LIF (266,nm) detector inside the cassette of a CE instrument and its performance was evaluated. The observed sensitivity was very close to that obtained by silver staining of slab gels (LOD of 25,ng/mL), while the sensitivity of the analysis is 80 times better than with CE/UV absorption (214,nm). Examples of the analysis of pharmaceutical and other commercial IgGs are provided and the kinetics of the reduction of IgG by ,-mercaptoethanol is reported, demonstrating the ease of performing the analysis. [source]

    Filmy channel microchip with amperometric detection

    ELECTROPHORESIS, Issue 22 2009
    Wei Wang
    Abstract In this article, a new type of microchip with filmy channels and a sample-injection fracture is introduced. Unlike commercial microchip, new microchip possessed filmy channel with width 2,3,mm. The effective cooling ability made filmy channel microchip restrain the generation of Joule heat even under electric field of 588,V/cm. Moreover, wider channel could be more easily modified to prevent the absorption of samples, load more samples and result in a higher sensitivity. Sample-injection fracture was first applied to match the filmy channel in microchip. Equipped with an amperometric detector, the characteristics of the newly designed filmy channel microchip had been studied and the results showed that it had good reproducibility, higher sensitivity and excellent separation ability. The microchip was also applied to separate L -tryptophan's metabolites, namely 5-hydroxy- L -tryptophan, 5-hydroxytryptamine and 5-hydroxy-indole-3-acetic acid. [source]

    Effects of heterogeneous electron-transfer rate on the resolution of electrophoretic separations based on microfluidics with end-column electrochemical detection

    ELECTROPHORESIS, Issue 19 2009
    Joseph 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 detector

    ELECTROPHORESIS, Issue 19 2009
    Dexian 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 in low-temperature co-fired ceramics technology with contactless conductivity measurement

    ELECTROPHORESIS, Issue 14 2009
    Georg Fercher
    Abstract In this paper a novel micromachined contactless conductivity CE device produced in low temperature co-fired ceramics (LTCC) is introduced. The application of LTCC multilayer technology provides a promising method for the contactless detection of conductive compounds because of its increased dielectric constant compared with glass or plastics. The capacitive coupling of the excitation signal into the microchannel across the LTCC substrate is improved, resulting in better detection sensitivity. Two silver electrodes located externally at opposite sides at the end of the separation channel act as detector. Impedance variations in the channel are measured without galvanic contact between electrodes and fluid. Inorganic ions are separated in less than 1,min with this novel ceramic device. The limit of detection is 10,,M for potassium. [source]

    MCE-electrochemical detection for following interactions of ssDNA and dsDNA with methylene blue

    ELECTROPHORESIS, Issue 11 2009
    Mario Castaño-Álvarez
    Abstract The interaction between the organic dye, methylene blue and DNA has been studied by MCE with electrochemical detection. Interaction produces two different signals, one corresponding to free methylene blue and other, for the complex methylene blue,DNA. The hybridization between a ssDNA and a complementary sequence, specific to the severe acute respiratory syndrome virus, has been performed and studied in a thermoplastic olefin polymer of amorphous structure CE-microchip with an end-channel gold wire detector. Moreover, studies with a longer dsDNA, an expression vector involved in the transitory or stable expression in mammals cells, pFLAG-CMV4, has also been performed. [source]

    Cover Picture: Electrophoresis 3'09

    ELECTROPHORESIS, Issue 3 2009
    Article first published online: 11 FEB 200
    This is a regular issue with an emphasis on "Fundamentals Methodologies and Instrumentation" assembling 11 articles in various research areas on fundamentals, methods development, instrumental design, detection and sensitivity enhancement approaches. The remaining articles are on proteins and proteomics analyses by various electrophoretic approaches. Selected topics of issue 3 are: Capillary Electrophoresis-based detection of Methicillin-resistant Staphylococcus aureus (MRSA CE-based detection of methicillin-resistant Staphylococcus aureus A portable capillary electropherograph equipped with a cross-sampler and a contactless-conductivity detector for the detection of the degradation products of chemical warfare agents in soil extracts Two-dimensional phosphate-affinity gel electrophoresis for the analysis of phosphoprotein isotypes [source]

    Competitive immunoassay by capillary electrophoresis with laser-induced fluorescence for the trace detection of chloramphenicol in animal-derived foods

    ELECTROPHORESIS, Issue 16 2008
    Can Zhang
    Abstract A competitive immunoassay using CE with an LIF detector was developed for the detection of chloramphenicol (CAP). The method was based on the competitive reactions between fluorescently labeled CAP hapten and free CAP, with a limited amount of anti-CAP antibody. The poly(N -isopropylacrylamide) (pNIPA) hydrogel was added in the separation buffer as a dynamic modifier to reduce adsorption and enhance reproducibility. The linear range and LOD for CAP were 0.008,5,,g/L and 0.0016,,g/L, respectively. An ELISA using the same immuno-reagents was also developed for the analysis of CAP, with an LOD of 0.03,,g/L. The sensitivity of this CE immunoassay (CEIA)-LIF was almost 20 times greater than that of the ELISA. Using CEIA-LIF, equilibrium was reached in 15,min and the analytical results were obtained within 5,min by CE separation. Sample preparation for CEIA-LIF was not time-consuming and the matrix effect was easy to remove. An LOD of 0.1,,g/kg CAP in food matrices was easily achieved. This method is thus proposed as a fast and sensitive means of detecting trace amounts of CAP residues in animal-derived foods. [source]