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Sample Injection (sample + injection)
Selected AbstractsField-amplified sample injection-micellar electrokinetic capillary chromatography for the analysis of bisphenol A, bisphenol F, and their diglycidyl ethers and derivatives in canned soft drinksELECTROPHORESIS, Issue 9 2010Héctor Gallart-Ayala Abstract Conditions were established for the separation and analysis of bisphenol A, bisphenol F, and their diglycidyl ethers by micellar electrokinetic capillary chromatography (MECC). Good resolution was obtained for all compounds, although in order to achieve the separation of ortho,ortho, ortho,para, and para,para isomers of bisphenol F diglycidyl ether (BFDGE), BFDGE·2H2O and BFDGE·2HCl, it was necessary to use a 25,,m id fused silica capillary. To increase sensitivity, a field-amplified sample injection (FASI)-MECC method was developed using 10,mM SDS solution as injection matrix and a 75,,m id fused silica capillary. Instrumental quality parameters such as LODs (<55,,g/L with standards), linearity (r2>0.999), and run-to-run and day-to-day precisions (RSD values lower than 12.5%) were determined. Finally, the suitability of the FASI-MECC method for the analysis of bisphenol A, bisphenol F, and their diglycidyl ethers in canned soft drinks was evaluated. Quantitation was performed by matrix-matched calibration using a plastic-bottled isotonic drink as matrix. The results showed that FASI-MECC is an economic method for the screening and quantitation of these kinds of compounds in soft drink beverages, with no loss of reproducibility, and effective at concentrations lower than the specific migration level values established by the European Union. [source] An accessible micro-capillary electrophoresis device using surface-tension-driven flowELECTROPHORESIS, Issue 9 2009Swomitra K. Mohanty Abstract We present a rapidly fabricated micro-capillary electrophoresis chip that utilizes surface-tension-driven flow for sample injection and extraction of DNA. Surface-tension-driven flow (i.e. passive pumping) [G. M. Walker et al., Lab. Chip. 2002, 2, 131,134] injects a fixed volume of sample that can be predicted mathematically. Passive pumping eliminates the need for tubing, valves, syringe pumps, and other equipment typically needed for interfacing with microelectrophoresis chips. This method requires a standard micropipette to load samples before separation, and remove the resulting bands after analysis. The device was made using liquid phase photopolymerization to rapidly fabricate the chip without the need of special equipment typically associated with the construction of microelectrophoresis chips (e.g. cleanroom) [A. K. Agarwal et al., J. Micromech. Microeng. 2006, 16, 332,340; S. K. Mohanty et al., Electrophoresis 2006, 27, 3772,3778]. Batch fabrication time for the device presented here was 1.5,h including channel coating time to suppress electroosmotic flow. Devices were constructed out of poly-isobornyl acrylate and glass. A standard microscope with a UV source was used for sample detection. Separations were demonstrated using Promega BenchTop 100,bp ladder in hydroxyl ethyl cellulose (HEC) and oligonucleotides of 91 and 118,bp were used to characterize sample injection and extraction of DNA bands. The end result was an inexpensive micro-capillary electrophoresis device that uses tools (e.g. micropipette, electrophoretic power supplies, and microscopes) already present in most labs for sample manipulation and detection, making it more accessible for potential end users. [source] SPE and large-volume sample stacking in MEKC for determination of doxycycline in biological fluids: Comparison of direct injection to SPE-MEKCELECTROPHORESIS, Issue 21 2008Rade Injac Abstract A novel and simple method has been developed for the determination of doxycycline (DOX) in biological fluids. The method is based on SPE, large-volume sample stacking (LVSS) and MEKC with UV-DAD detection. Six SPE cartridges have been used in investigation for sample clean up and pre-concentration (Supelco® LC-8, LC-18, LC-SCX, and LC-WCX, as well as StrataÔ-X and X-C). DOX was determined on a 56,cm (effective length 50,cm)×50,,m id fused-silica capillary. The BGE was 20,mM borate buffer, pH 9.3, containing 80,mM SDS and 7.5%,v/v of methanol (30,s×50,mbar), and the temperature and voltage were 25°C and 30,kV, respectively. The analytical wavelength was set at 210,nm. Under optimized conditions it is possible to determine DOX in human serum, urine, semen, tears and saliva with recovery of 97.5% (RSD 2.5%). The method was shown to be sensitive (LOD is 1,,g/L) and precise (intra-day RSD 0.2 and 2.4%; inter-days 0.4 and 3.5% for migration time and peak area, respectively). Results for developed SPE-LVSS-MEKC were compared with LVSS-MEKC method with direct sample injection. The new LVSS-MEKC method is presented as a useful technique for rapid determination without extraction procedure of DOX in human urine and serum, using 80,mM of SDS, 10%,v/v of methanol and 40,mM borate buffer (pH 9.3; 30,s×50,mbar; 25°C; 30,kV; 350,nm), but not for the other biological fluids, according to lower sensitivity of the method and because of the sample composition. [source] Capillary electrophoresis-time of flight-mass spectrometry using noncovalently bilayer-coated capillaries for the analysis of amino acids in human urineELECTROPHORESIS, Issue 12 2008Rawi Ramautar Abstract A capillary electrophoresis-time of flight-mass spectrometry (CE-TOF-MS) method for the analysis of amino acids in human urine was developed. Capillaries noncovalently coated with a bilayer of Polybrene (PB) and poly(vinyl sulfonate) (PVS) provided a considerable EOF at low pH, thus facilitating the fast separation of amino acids using a BGE of 1,M formic acid (pH,1.8). The PB,PVS coating proved to be very consistent yielding stable CE-MS patterns of amino acids in urine with favorable migration time repeatability (RSDs <2%). The relatively low sample loading capacity of CE was circumvented by an in-capillary preconcentration step based on pH-mediated stacking allowing 100-nL sample injection (i.e. ca. 4% of capillary volume). As a result, LODs for amino acids were down to 20,nM while achieving satisfactory separation efficiencies. Preliminary validation of the method with urine samples showed good linear responses for the amino acids (R2 >0.99), and RSDs for peak areas were <10%. Special attention was paid to the influence of matrix effects on the quantification of amino acids. The magnitude of ion suppression by the matrix was similar for different urine samples. The CE-TOF-MS method was used for the analysis of urine samples of patients with urinary tract infection (UTI). Concentrations of a subset of amino acids were determined and compared with concentrations in urine of healthy controls. Furthermore, partial least squares,discriminant analysis (PLS,DA) of the CE-TOF-MS dataset in the 50,450,m/z region showed a distinctive grouping of the UTI samples and the control samples. Examination of score and loadings plot revealed a number of compounds, including phenylalanine, to be responsible for grouping of the samples. Thus, the CE-TOF-MS method shows good potential for the screening of body fluids based on the analysis of endogenous low-molecular weight metabolites such as amino acids and related compounds. [source] Application of CE with novel dynamic coatings and field-amplified sample injection to the sensitive determination of isomeric benzoic acids in atmospheric aerosols and vehicular emissionELECTROPHORESIS, Issue 19 2007Ewa Dabek-Zlotorzynska Dr. Abstract A simple and reliable CE method with direct UV detection has been developed to separate eight isomeric benzoic acids in atmospheric aerosols and vehicular emission without complex sample pretreatment. Optimal electrophoretic conditions, with migration times under 5,min, were obtained by using a 50,mM acetate buffer (pH,4.7) containing a dynamic surface coating EOTrolÔ LN (0.005% w/v). The separations were carried out in a cathode to anode direction (,30,kV) allowing the low cathodal EOF (,1×10,9,m2V,1s,1) to extend the effective separation by slowing the movement of the studied aromatic acids. Moreover, the sensitivity of the method at 200,nm was enhanced by using a field-amplified sample injection (FASI) with electrokinetic (EK) sample injection (,2,kV, 60,s). Prior to sample injection, a short water plug (3,s at 0.5,psi) was introduced. Under these conditions, the method was capable of detecting the analytes in deionized water with LODs (S/N,=,3) as low as 0.1,,g/L for most of the studied acids. In the presence of 10,mg/L of sulphate (added to simulate a sample matrix), LODs ranged from 0.26 to 0.62,,g/L. The validation of the method has proven an excellent separation performance and accuracy for the determination of isomeric benzoic acids in the studied matrices. [source] High-sensitivity detection of biological amines using fast Hadamard transform CE coupled with photolytic optical gatingELECTROPHORESIS, Issue 17 2007Kevin L. Braun Abstract Here, we report the first utilization of Hadamard transform CE (HTCE), a high-sensitivity, multiplexed CE technique, with photolytic optical gating sample injection of caged fluorescent labels for the detection of biologically important amines. Previous implementations of HTCE have relied upon photobleaching optical gating sample injection of fluorescent dyes. Photolysis of caged fluorescent labels reduces the fluorescence background, providing marked enhancements in sensitivity compared to photobleaching. Application of fast Hadamard transform CE (fHTCE) for fluorescein-based dyes yields a ten-fold higher sensitivity for photolytic injections compared to photobleaching injections, due primarily to the reduced fluorescent background provided by caged fluorescent dyes. Detection limits as low as 5,pM (ca. 18,molecules per injection event) were obtained with on-column LIF detection using fHTCE in less than 25,s, with the capacity for continuous, online separations. Detection limits for glutamate and aspartate below 150,pM (1,2,amol/injection event) were obtained using photolytic sample injection, with separation efficiencies exceeding 1×106,plates/m and total multiplexed separation times as low as 8,s. These results strongly support the feasibility of this approach for high-sensitivity dynamic chemical monitoring applications. [source] Application of Hadamard transformation to MEKCELECTROPHORESIS, Issue 3 2007Kazuki Hata Abstract The Hadamard transform (HT) technique, which permits the S/N in CE to be improved, was applied to MEKC. Multiple sample injection of fluorescent analytes according to a Hadamard code sequence was performed using an optically gated sample injection technique, in which a sample plug was produced based on photodegradation by irradiation with an intense laser beam. The capillary and reservoirs were filled with a sample solution containing buffer components and SDS as a pseudostationary phase. A preliminary study confirmed that fluorescein ion could be photobleached in the presence of SDS. The optically gated sample injection technique was then applied to multiple sample injection, based on a Hadamard matrix. The S/N in the electropherogram obtained by HT-MEKC was improved substantially compared to that obtained by a single injection method. When the technique was applied to the separation of several amino acids labeled with FITC, the S/N ratio for each amino acid was enhanced, without any evidence of degradation in separation resolution. Moreover, HT-MEKC was applied to the analysis of amino acids contained in a Japanese beverage, resulting in improved S/Ns for the amino acids. [source] Speciation of selenium compounds by open tubular capillary electrochromatography-inductively coupled plasma mass spectrometryELECTROPHORESIS, Issue 21 2006Shu-Yu Lin Abstract We introduce a T-type interface and a crossflow nebulizer to find ways to combine CEC with inductively coupled plasma MS (ICP-MS) detection for selenium speciation. For CEC separation, we employed a macrocyclic polyamine-bonded phase capillary as the separation column and a bare fused-silica capillary filled with the make-up liquid (0.05,M,HNO3). The effect of nebulizer gas flow rate, make-up liquid flow, type, concentration and pH of the mobile phase on the separation have been studied. Tris buffer of 50,mM at pH,8.50 gave the best performance for selenium speciation. The reproducibility of the retention time indicated that sample injection by electrokinetic and nebulizer gas flow was better than that by self-aspiration alone. The detection limits for selenate, selenite, selenocystine and selenomethionine were found to be 2.40, 3.53, 12.86 and 11.25,ng/mL, respectively. Due to the high sensitivity and element-specific detection, as well as the high selectivity of the bonded phase, quantitative analysis of selenium speciation in urine was also achieved. [source] A novel ultra-sensitive method for the quantification of glycosaminoglycan disaccharides using an automated DNA sequencerELECTROPHORESIS, Issue 7 2006Kay Vogel Abstract Analysis of glycosaminoglycans (GAGs) is of increasing importance concerning alterations in extracellular matrix composition and selectivity of glomerular basement membrane. In this report we describe the analysis of chondroitin sulfate disaccharides as an example of GAG ,disaccharide analysis using standard DNA sequencing equipment (DNA sequencer-assisted GAG disaccharide separation, DSA-GAGS). The presented methodology allows nanomolar quantification of 8-aminopyrene-1,3,6-trisulfonic acid (APTS)-derived GAG disaccharides. In comparison to RP-HPLC the established method is much more sensitive, showing detection limits of 38,fmol/,L. Variation coefficients were approximately 10%, enabling exact quantifications after run times of 17,min at 30°C and an electrophoresis voltage of 15,kV; using a capillary DNA sequencer, available in many molecular laboratories, presented advantages like automated sample injection, opportunity of high-throughput analyses, separation of even sulfated disaccharide epimers, and the possibility of using APTS-derived fucose as an internal standard. Furthermore, highly reproducible retention times rendered easy identification of specific signals (SD,0.02). With regard to these results, the described method is a useful tool for the quantification of GAG disaccharides in low amounts, indicating advantages of obverse RP-HPLC and slab gel polyacrylamide electrophoresis in sensitivity, error-proneness, automation, and handling. [source] Rapid determination of acyclovir in plasma and cerebrospinal fluid by micellar electrokinetic chromatography with direct sample injection and its clinical applicationELECTROPHORESIS, Issue 4 2006Hsin-Hua Yeh Abstract A simple MEKC with UV detection at 254,nm for analysis of acyclovir in plasma and in cerebrospinal fluid (CSF) by direct injection without any sample pretreatment is described. The separation of acyclovir from biological matrix was performed at 25°C using a BGE consisting of Tris buffer with SDS as the electrolyte solution. Several parameters affecting the separation of the drug from biological matrix were studied, including the pH and concentrations of the Tris buffer and SDS. Using dyphylline as an internal standard, the linear ranges of the method for the determination of acyclovir in plasma and in CSF all exceeded the range of 2,50,,g/mL; the detection limit of the drug in plasma and in CSF (S/N = 3; injection 3.45,kPa, 5,s) was 1.0,,g/mL. The applicability of the proposed method for determination of acyclovir in plasma and CSF collected at 8,h after intravenous administration of 500,mg acyclovir (Zovirax®) in two patients with herpes simplex encephalitis was demonstrated. [source] Electrokinetic-driven microfluidic system in poly(dimethylsiloxane) for mass spectrometry detection integrating sample injection, capillary electrophoresis, and electrospray emitter on-chipELECTROPHORESIS, Issue 24 2005Sara Thorslund Abstract A novel microsystem device in poly(dimethylsiloxane) (PDMS) for MS detection is presented. The microchip integrates sample injection, capillary electrophoretic separation, and electrospray emitter in a single substrate, and all modules are fabricated in the PDMS bulk material. The injection and separation flow is driven electrokinetically and the total amount of external equipment needed consists of a three-channel high-voltage power supply. The instant switching between sample injection and separation is performed through a series of low-cost relays, limiting the separation field strength to a maximum of 270,V/cm. We show that this set-up is sufficient to accomplish electrospray MS analysis and, to a moderate extent, microchip separation of standard peptides. A new method of instant in-channel oxidation makes it possible to overcome the problem of irreversibly bonded PDMS channels that have recovered their hydrophobic properties over time. The fast method turns the channel surfaces hydrophilic and less prone to nonspecific analyte adsorption, yielding better separation efficiencies and higher apparent peptide mobilities. [source] A multilayer poly(dimethylsiloxane) electrospray ionization emitter for sample injection and online mass spectrometric detectionELECTROPHORESIS, Issue 24 2005Jamie M. Iannacone Abstract An ESI emitter made of poly(dimethylsiloxane) interfaces on-chip sample preparation with MS detection. The unique multilayer design allows both the analyte and the spray solutions to reside on the device simultaneously in discrete microfluidic environments that are spatially separated by a polycarbonate track-etched, nanocapillary array membrane (NCAM). In direct spray mode, voltage is applied to the microchannel containing a spray solution delivered via a syringe pump. For injection, the spray potential is lowered and a voltage is applied that forward biases the membrane and permits the analyte to enter the spray channel. Once the injection is complete, the bias potential is switched off, and the spray voltage is increased to generate the ESI of the injected analyte plug. Consecutive injections of a 10,,M bovine insulin solution are reproducible and produce sample plugs with limited band broadening and high quality mass spectra. Peptide signals are observed following transport through the NCAM, even when the peptide is dissolved in solutions containing up to 20% seawater. The multilayer emitter shows great potential for performing multidimensional chemical manipulations on-chip, followed by direct ESI with negligible dead volume for online MS analysis. [source] Modified Hadamard transform microchip electrophoresisELECTROPHORESIS, Issue 16 2005Renato Guchardi Abstract Sensitivity is a crucial point in the development applications for medicine or environmental samples in which the analytes are present in the nanomolar range. Besides further technical development of detection systems, the multiplex sample injection technique can be applied for enhancing the signal-to-noise ratio. Hadamard transform is easily applied to microchip electrophoresis due to the fact that sample injection is generally achieved through cross, double-tee, or tee injector structures. This paper reports the first demonstration of a modified Hadamard transform electrophoresis on a microchip by using an amperometric detector. Contrary to the previous Hadamard applications, the resolution (number of points per unit of time) of electropherograms obtained is independent of the number of injections. [source] Microautosamplers for discrete sample injection and dispensationELECTROPHORESIS, Issue 9 2005Chun-Wei Huang Abstract Microfluidic systems show considerable potential for use in the continuous reaction and analysis of biosamples for various applications, such as drug screening and chemical synthesis. Typically, microfluidic chips are externally connected with large-scale autosamplers to inject specific volumes of discrete samples in the continuous monitoring and analysis of multiple samples. This paper presents a novel microelectromechanical system (MEMS)-based autosampler capable of performing the discrete injection and dispensation of variable-volume samples. This microdevice can be integrated with other microfluidic devices to facilitate the continuous monitoring and analysis of multiple biosamples. By means of electroosmotic focusing and switching controlled by the direct application of electric sources on specific fluid reservoirs, a precise sample volume can be injected into the specified outlet port. Fluorescence dye images verify the performance of the developed device. An injection-and-washing scheme is developed to prevent cross-contamination during the continuous injection of different samples. This approach renders feasible the injection of several discrete samples using a single microchip. Compared to its large-scale counterparts, the developed microautosampler is compact in size, has low fabrication costs, is straightforward to control, and most importantly, is readily integrated with other microfluidic devices (e.g., microcapillary electrophoresis chips) to form a microfluidic system capable of the continuous monitoring and analysis of bioreactions. The proposed microautosampler could be promising towards realizing the micrototal analysis system (,-TAS) concept. [source] Comparison of two capillary electrophoresis online stacking modes by analysis of polycyclic aromatic hydrocarbons in airborne particulatesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 13 2006Guan-Qun Song Abstract Naphthalene, fluorene, pyrene, anthracene, phenanthrene, and chrysene were successfully separated by CD-modified MEKC (CD-MEKC) using 20 mM borate (pH 9.0) containing 90 mM SDS and 75 mM ,-CD. Two online stacking methods, i. e., sweeping and field-enhanced sample injection (FESI), were explored to enhance the detection sensitivity. The influences of some crucial parameters in sweeping and FESI procedures were investigated. For FESI method, a plug of water and low-conductivity sample matrix was used to increase the stacking efficiency. Compared with the sweeping method, FESI can increase the sensitivity in the range of 10,20-fold. The proposed method was used for the analysis of polycyclic aromatic hydrocarbons in airborne particulates. [source] Field-amplified on-line sample stacking for determination of carnosine-related peptides by capillary electrophoresisJOURNAL OF SEPARATION SCIENCE, JSS, Issue 7 2006Ying Huang Abstract An on-line sample stacking method, namely field-amplified sample injection, has been developed for the separation and determination of carnosine, anserine, and homocarnosine by capillary electrophoresis. Using electrokinetic injection, about 130- to 160-fold improvement of sensitivity was achieved without loss of separation efficiency when compared to conventional sample injection. For conventional injection, the samples were dissolved in running buffer and then hydrodynamically injected for 10 s (3.45 kPa). Various parameters affecting separation and sample stacking were optimized. Under optimum conditions, linear responses were obtained over two orders of magnitude and the detection limits (defined as S/N = 3) of carnosine, anserine, and homocarnosine were 1.5×10,8 to 1.6×10,8 mol/L. [source] Analysis of isomeric tropane alkaloids from Schizanthus grahamii by very fast gas chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 1 2006Stefan Bieri Abstract This study presents a very fast GC analysis applied for the baseline separation of isomeric tropane alkaloids extracted from the stem-bark of Schizanthus grahamii (Solanaceae). The work provided a challenging application where isothermal analysis in conjunction with very short narrow bore columns (3 m×100 ,m ID and 1.5 m×50 ,m ID) was particularly suited for the speeding up. Experimental parameters were used in the optimisation steps, including selection of stationary phase, temperature, internal column diameter and optimal practicable gas velocity. Some considerations about sample injection in fast isothermal analysis are also briefly presented. Finally, the investigated approach allowed a very fast baseline separation of four positional and configurational isomers in less than 9 s. [source] On-line concentration by field-enhanced sample injection with reverse migrating micelles in micellar electrokinetic capillary chromatography for the analysis of coumarins from traditional Chinese medicine and human serumBIOMEDICAL CHROMATOGRAPHY, Issue 6 2010Ting-Fu Jiang Abstract In this work, a simple, reproducible and sensitive micellar electrokinetic chromatography method was developed for the separation and determination of three coumarins, imperatorin (IM), isoimperatorin (IO) and osthole (OS) from traditional Chinese medicine and human serum. Field-enhanced sample injection with reverse migrating micelles was used for on-line concentration of the coumarins. The optimum buffer contained 50,mM H3PO4, 160,mM sodium dodecyl sulfate, 20% acetonitrile and 15% 2-propanol, and the pH of buffer was 2.0. The sample solution was diluted with water containing 5,mM sodium dodecyl sulfate and injected for 15,s with ,8,kV after injection of 2,s water plug. The effects of concentrations of sodium dodecyl sulfate and organic modifier, the sample matrix, the injection time of water plug, the injection voltage and injection time of sample on the separation and stacking efficiency were investigated. Under the optimum conditions, the analytes were well separated and by optimizing the stacking conditions, about 93, 195 and 136 fold improvement in the detection sensitivity was obtained for IM, IO and OS. The contents of three coumarins in Angelica dahurica Benth, Radix Angelicae Pubescentis and Fructus Cnidii were successfully determined with satisfactory repeatability and recovery. The possibilities of using this method for the determination of three coumarins in spiked human serum were also tested. Copyright © 2009 John Wiley & Sons, Ltd. [source] Microfluidic devices for electrokinetic sample fractionationELECTROPHORESIS, Issue 15 2010Zhen Wang Abstract We present three generations of microchip-based "in-space" sample fractionators and collectors for use in proteomics. The basic chip design consisted of a single channel for CE separation of analytes that then intersects a fractionation zone feed into multiple high aspect ratio microchannels for fractionation of separated components. Achievements of each generation are discussed in relation to important design criteria. CE-separated samples were electrokinetically driven to multiple collection channels in sequence without cross-contamination under the protection of sheath streams. A 36-channel fractionator demonstrated the efficacy of a high-throughput fractionator with no observed cross-contamination. A mixture of IgG and BSA was used to test the efficiency of the fractionator and collector. CE of the fractionated samples was performed on the same device to verify their purity. Our demonstration proved to be efficient and reproducible in obtaining non-contaminated samples over 15 sample injections. Experimental results were found to be in close agreement with PSpice simulation in terms of flow behavior, contamination control and device performance. The design presented here has a great potential to be integrated in proteomic platforms. [source] A sweeping-micellar electrokinetic chromatography method for direct detection of some aromatic amines in water samplesELECTROPHORESIS, Issue 4 2008Jianhua Zhang Abstract A simple and rapid sweeping method for the online improvement of detection limit of some aromatic amines has been developed in this work. The optimum sweeping and separation conditions for 4-methylaniline, 3,4-dichloroaniline, 4-chloroaniline, and 4-aminophenyl were investigated in detail. Under the optimum conditions, the detection limits of these four aromatic amines ranged from 5.4×10,10 to 4.6×10,8,mol/L (S/N,=,3), which was about 80,1090-folds lower than those of conventional sample injections. Linear response range were in the range of 2.5×10,8,2.0×10,6,mol/L with the correlation coefficient between 0.9965 and 0.9994. Baseline separation was achieved within 10,min. After validation, the developed method was applied to determine 4-methylaniline, 3,4-dichloroaniline, 4-chloroaniline, and 4-aminophenyl in river water sample with average recoveries of 79.6,88.7%. [source] Microchip capillary electrophoresis with a cellulose-DNA-modified screen-printed electrode for the analysis of neurotransmittersELECTROPHORESIS, Issue 15 2005Muhammad Johirul Abstract A microfluidic chip based on capillary electrophoresis coupled with a cellulose-single-stranded DNA (cellulose-ssDNA) modified electrode was used for the simultaneous analysis of dopamine (DA), norepinephrine (NE), 3,4-dihydroxy- L -phenylalanine (L -DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), and ascorbic acid (AA). The modification of the electrode improved the electrophoretic analysis performance by lowering the detection potential and enhancing the signal-to-noise characteristic without surface poisoning of the electrode. The sensitivity of the modified electrode was about 12 times higher than those of the bare ones. The test compounds were separated using a 62,mm long separation channel at the separation field strength of +200,V/cm within 220,s in a 10,mM phosphate buffer (pH,7.4). The most favorable potential for the amperometric detection was 0.7,V (vs. Ag/AgCl). A reproducible response (relative standard deviation of 1.3, 1.3, 2.1, 3.1, 3.4% for DA, NE, L -DOPA, DOPAC, and AA, respectively, for n,=,9) for repetitive sample injections reflected the negligible electrode fouling at the cellulose-ssDNA modified electrode. Square-wave voltammetric analyses reflected the sensitivities of the modified electrode for DA, NE, L -DOPA, DOPAC, and AA which were 1.78, 0.82, 0.69, 2.45, and 1.23,nC/µM with detection limits of 0.032, 0.93, 1.13, 0.31, and 0.62,µM, respectively. The applicability of this microsystem to real sample analysis was demonstrated. [source] Packing capillary electrochromatography columns using vacuum , A preliminary studyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 14 2004Qishu Qu Abstract This paper introduces a novel method for packing Capillary Electrochromatography Columns (CEC). Using vacuum packing methodology, silica particles as small as 1 ,m were successfully packed into the capillary columns with 75 ,m inner diameter. The columns are very stable and show no noticeable loss in efficiency after 200 sample injections. The performance of these vacuum packed capillary columns was evaluated with a mixture of aromatic and non-aromatic compounds. A 24 cm long capillary column can produce peak efficiencies of around 45 000 plates for benzene. [source] The design of an on-line semi-preparative LC,SPE,NMR system for trace analysis,MAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2005Feng Xu Abstract This paper reports the design of an on-line semi-preparative LC,SPE,NMR system and its use in the structural analysis of mixture components at the 0.02,1% level. The combination provides at least a five fold mass sensitivity increase over that obtained from typical analytical LC,SPE systems and a >30-fold total NMR sensitivity enhancement over analysis by LC,NMR. This is accomplished by using a novel on-line device to store, dilute (1,100-fold) and deliver (at an optimized flow-rate) the isolated component of interest to an SPE trap unit. The SPE unit consists of two cartridges connected in parallel to increase the overall SPE capacity and also to decrease the flow-rate through each trap for enhanced trapping efficiency. As the coupling of semi-preparative LC with NMR (through SPE) is well matched in terms of optimal mass loading for both techniques, only one LC,SPE cycle is required to enrich a 50 µg ml,1 component (1% in a 5 mg ml,1 mixture) for the acquisition of heteronuclear 1H,13C NMR data using a conventional NMR flow probe. Furthermore, analytes at the 0.02% level (,1 µg ml,1) can be studied using 2D 1H NMR techniques if peak cuts from replicate sample injections (,3) are accumulated into the storage/dilution unit and the resulting solution processed by just one SPE trap and elute cycle. Copyright © 2005 John Wiley & Sons, Ltd. 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