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Separation Performance (separation + performance)
Selected AbstractsSeparation and Detection of Narcotic Drugs on a Microchip Using Micellar Electrokinetic Chromatography and ElectrochemiluminescenceELECTROANALYSIS, Issue 6 2008Yan Du Abstract A new approach for fast and sensitive electrochemiluminescence (ECL) detection of narcotic drugs on a microchip after separation by micellar electrokinetic chromatography (MEKC) is presented, taking the cocaine and its hydrolysate ecgonine as the test analytes. The mixture of hydrophilic BMIMBF4 ionic liquid (IL) and sodium dodecyl sulfate (SDS) was used directly as the buffer of MEKC with less noisy baselines, lower electrophoretic current and satisfactory separation performance. This developed microchip MEKC,ECL system was successfully applied to the determination of two very similar narcotics, heroin and codeine, within 100s in urine sample and was demonstrated as a promising method in clinical and forensic analysis. [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] IEF in microfluidic devicesELECTROPHORESIS, Issue 5 2009Greg J. Sommer Abstract IEF is one of the most powerful and prevalent techniques used in separation sciences. The power of IEF comes from the fact that it not only separates analytes based on their pI but also focuses them into highly resolved bands. In line with the miniaturization trend spurring the analytical community, the past decade has yielded a wealth of research focused on implementing IEF in microfluidic chip-based formats (,IEF). Scaling down the separation technique provides several advantages such as reduced sample sizes, assay automation, and significant improvements in assay speed without sacrificing separation performance. Besides presenting microscale adaptations of standard schemes, researchers have also developed improved detection techniques, demonstrated novel ,IEF assays, and incorporated ,IEF with other analytical methods for achieving on-chip multidimensional separations. This review provides a brief historical outline of IEF's beginnings, theoretical incentives driving miniaturization of the methodology, a thorough synopsis of ,IEF publications to date, and an outlook to the future. [source] Investigating DNA migration in pulsed fields using a miniaturized FIGE systemELECTROPHORESIS, Issue 23 2008Xiaojia Chen Abstract PFGE is a well-established technique for fractionation of DNA fragments ranging from kilobases to megabases in length. But many of these separations require an undesirable combination of long experiment times (often approaching tens of hours) and application of high voltages (often approaching tens of kV). Here, we present a simple miniaturized FIGE apparatus capable of separating DNA fragments up to 32.5,kb in length within 3,h using a modest applied potential of 20,V. The device is small enough to be imaged under a fluorescence microscope, permitting the migrating DNA bands to be observed during the course of the separation run. We use this capability to investigate how separation performance is affected by parameters including the ratio of forward and backward voltage, pulse time, and temperature. We also characterize the dependence of DNA mobility on fragment size N, and observe a scaling in the vicinity of N,0.5 over the size range investigated. The high speed, low power consumption, and simple design of this system may help enable future studies of DNA migration in PFGE to be performed quickly and inexpensively. [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] SDS-CGE of proteins in microchannels made of SU-8 filmsELECTROPHORESIS, Issue 18 2006Maria Agirregabiria Abstract This work describes the SDS-CGE of proteins carried out in microchannels made of the negative photoresist EPON SU-8. Embedded electrophoretic microchannels have been fabricated with a multilayer technology based on bonding and releasing steps of stacked SU-8 films. This technology allows the monolithic integration of the electrodes in the device. A high wafer fabrication yield and mass production compatibility guarantees low costs and high reliability. A poly(methyl methacrylate) (PMMA) packaging allows an easy setup and replacement of the device for electrophoresis experiments. In addition, the wire-bonding step is avoided. The electrophoretic mobilities of four proteins have been measured in microchannels filled with polyacrylamide. Different pore sizes have been tested obtaining their Ferguson plots. Finally, a separation of two proteins (20 and 36,kDa) has been carried out confirming that this novel device is suitable for protein separation. A resolution of 2.75 is obtained. This is the first time that this SU-8 microfluidic technology has been validated for SDS-CGE of proteins. This technology offers better separation performance than glass channels, at lower costs and with an easy packaging procedure. [source] Microemulsion electrokinetic chromatography of drugs varying in charge and hydrophobicity: I. Impact of parameters on separation performance evaluated by multiple linear regression modelsELECTROPHORESIS, Issue 1 2004Valérie Harang Abstract The separation of anionic, cationic and neutral drugs in microemulsion electrokinetic chromatography (MEEKC) was studied with a statistical experimental design. The concentration of sodium dodecyl sulfate (SDS, surfactant), 1-butanol (co-surfactant) and borate buffer and the factors Brij 35 (surfactant), 2-propanol (organic solvent) and cassette temperature were varied simultaneously, while the parameters pH (9.2), the concentration of octane (oil, 0.8% w/w), the voltage (10 kV) and the dimension of the fused-silica capillary, were kept constant. Eight different model substances were chosen with different hydrophobicities. Two of the analytes were positively charged, two were negatively charged, and the remaining four were neutral or close to neutral at the pH explored. The importance of each parameter on the separation window, the plate height and the retention factor for each of the analytes was studied by means of multiple linear regression (MLR) models. A new response was evaluated for anions, the quotient between the effective mobility in the microemulsion and the effective mobility in the corresponding buffer. Factors affecting selectivity changes were also explored, and it was found that SDS and 2-propanol had the largest effect on selectivity. [source] Recent progress in enantiomeric separation by capillary electrochromatographyELECTROPHORESIS, Issue 22-23 2002Jingwu Kang Abstract Recent progress in enantiomeric separations by capillary electrochromatography (CEC) is reviewed. The development of simple and robust CEC column technologies plays an important role for popularization of CEC. During the last several years, various approaches for the preparation of enantioselective columns have been reported. Currently, the monolithic column technology (continuous beds) represents the most advanced approach for the preparation of CEC columns. The development of new chiral stationary phase used for CEC is another important issue in this field. Fundamental investigations on electrochromatographic behaviors of various CSPs are necessary in order to understand the separation mechanism and thus improve the separation performance. Some chiral stationary phases performed better under nonaqueous CEC conditions than reversed-phase conditions. Coupling CEC with mass spectrometry (MS) provides a powerful tool for enantiomeric separation. Finally, some applications of enantiomeric separation by CEC are summarized. [source] Assessment of a semi-quantitative method for estimation of the rejection of organic compounds in aqueous solution in nanofiltrationJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2006Bart Van der Bruggen Abstract A large number of different mechanisms describing the retention of dissolved organic compounds in nanofiltration have been proposed. A recent review identified the parameters possibly involved in the separation performance and suggested a qualitative classification of dissolved compounds. Continuing this approach, a semi-quantitative assessment of the observed rejections in nanofiltration is given in this paper, based on threshold values of key parameters such as molecular weight and molecular weight cut-off (MWCO), molecular size, pH and pKa, hydrophobicity (logKow) and membrane charge. Experimental values and literature data were used to provide a broad basis for comparison. It was concluded that (a) all categories that contain hydrophobic components are badly defined, in particular for small components, with rejections varying from low to very high, (b) all components that contain hydrophilic components have relatively high rejections and (c) all categories that contain charged components have well-defined, high rejections (intermediate for membranes with low surface charge). In all cases, the average rejection is higher when the component's molecular weight is larger than the MWCO of the membrane and when the molecular size is larger than the pore size of the membrane. Copyright © 2006 Society of Chemical Industry [source] STUDY ON IMPROVEMENT OF THE QUALITY IN CHINESE NEW-TYPE LIQUOR BY PERVAPORATION WITH POLYDIMETHYLSILOXANE MEMBRANEJOURNAL OF FOOD PROCESS ENGINEERING, Issue 1 2007ER SHI ABSTRACT A composite polydimethylsiloxane (PDMS) membrane was used to separate aroma compounds from Chinese new-type liquor by pervaporation at 30, 35 and 40C and 10-mmHg downstream pressure. The gas chromatography analysis of aroma compounds in the retentate and permeate showed that PDMS membrane had excellent separation performance. Separation efficiencies for five kinds of esters (except ethyl lactate) and acetal in the original liquor are 100%, over 70% for alcohols (except methanol) and above 87% for aldehyde. The average flux for ethanol reached 3,539 g/m2 · h at 40C. Sensory analysis of the separated ingredients indicates that the sensory quality of the new liquor was significantly superior to that of the original liquor. Experiments suggest that pervaporation is a promising technique for the improvement of Chinese new-type liquor in terms of its flavor. [source] Enantioseparation via EIC-OSN: Process design and improvement of enantiomers resolvability and separation performanceAICHE JOURNAL, Issue 4 2010Issara Sereewatthanawut Abstract This article presents a mathematical model to assess and optimize the separation performance of an enantioselective inclusion complexation-organic solvent nanofiltration process. Enantiomer solubilities, feed concentrations, solvent compositions, permeate solvent volumes, and numbers of nanofiltrations were identified as key factors for process efficiency. The model was first tested by comparing calculated and experimental results for a nonoptimized process, and then, calculations were carried out to select the best operating conditions. An important finding was that the optimal configuration varied with the objective function selected, e.g., resolvability versus yield, with a boundary on product optical purity. The model also suggested that the process efficiency could benefit from diafiltration of the distomer and from the use of higher feed concentrations. However, the latter strategy would result in higher losses of eutomer. To address this drawback, a multistage process was evaluated using the verified process model. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Exploration of ionic modification in dual-layer hollow fiber membranes for long-term high-performance protein separationAICHE JOURNAL, Issue 2 2009Yi Li Abstract Two types of ionic modification approaches (i.e., sulfonation and triethylamination) were applied with the aid of dual-layer hollow fiber technology in this work to fine tune the pore size and pore size distribution, introduce the electrostatic interaction, and reduce membrane fouling for long-term high-performance protein separation. A binary protein mixture comprising bovine serum albumin (BSA) and hemoglobin (Hb) was separated in this work. The sulfonated fiber exhibits an improved BSA/Hb separation factor at pH = 6.8 compared with as-spun fibers but at the expense of BSA sieving coefficient. On the other hand, the triethylaminated fiber reveals the best and most durable separation performance at pH = 4.8. Its BSA/Hb separation factor is maintained above 80 for 4 days and maximum BSA sieving coefficient reaches 33%. Therefore, this study documents that an intelligent combination of both size-exclusion and electrostatic interaction can synergistically enhance protein separation performance in both purity and concentration. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Ultrathin polymeric interpenetration network with separation performance approaching ceramic membranes for biofuelAICHE JOURNAL, Issue 1 2009Lan Ying Jiang Abstract Biofuel has emerged as one of the most strategically important sustainable fuel sources. The success of biofuel development is not only dependent on the advances in genetic transformation of biomass into biofuel, but also on the breakthroughs in separation of biofuel from biomass. The "separation" alone currently accounts for 60,80% of the biofuel production cost. Ceramic membranes made of sophisticated processes have shown separation performance far superior to polymeric membranes, but suffers fragility and high fabrication cost. We report the discovery of novel molecular engineering and membrane fabrication that can synergistically produce polymeric membranes exhibiting separation performance approaching ceramic membranes. The newly discovered Polysulfone/Matrimid composite membranes are fabricated by dual-layer coextrusion technology in just one step through phase inversion. An ultrathin dense-selective layer made of an interpenetration network of the two materials with a targeted and stable interstitial space is formed at the interface of two layers for biofuel separation. The combined molecular engineering and membrane fabrication approach may revolutionize future membrane research and development for purification and separation in energy, environment, and pharmaceuticals. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Heat-exchange pressure swing adsorption process for hydrogen separationAICHE JOURNAL, Issue 8 2008Jang-Jae Lee Abstract A current focus in the energy field is on the use of hydrogen in fuel cells. Development of a hydrogen station system is important to the commercialization of fuel cells and fuel cell powered vehicles. In this study, the heat-exchange pressure swing adsorption (HE-PSA) was developed to design a compact H2 PSA process for small spatial occupancy in the hydrogen station. The adsorption dynamics and performance of the newly designed bed were compared with those of a conventional bed by using a quaternary mixture (H2/CO2/CH4/CO 69:26:3:2 vol %) which is generally obtained from the steam-reforming reaction of natural gas. Because the detrimental exothermic/endothermic heat effects accompanied by the adsorption/desorption steps were reduced by heat exchange between the adsorption beds, the separation performance of the HE-PSA was higher than that of a conventional PSA. In addition, the spatial occupancy of the beds could be significantly reduced, compared with a conventional PSA, because the single annular-type bed performed the function of two beds in the HE-PSA. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Hydrogen separation of methyltriethoxysilane templating silica membraneAICHE JOURNAL, Issue 12 2007Jong-Ho Moon Abstract Hydrogen separation on microporous methyltriethoxysilane-templating silica composite/,-alumina membranes (below MTES membrane) was studied using three binary gas mixtures: H2/N2, H2/CO2, and H2/CH4. The characteristics of unsteady and steady-state permeation/separation on the MTES membrane were compared to each other. Although permeation flux in the H2/N2 mixture was comparatively low, H2 selectivity was high (H2/N2 SF , 30,60). On the contrary, the H2/CO2 mixture showed high permeation flux but low H2 selectivity (H2/CO2 SF , 1.5,6.5). The H2/CH4 mixture showed a large difference between permselectivity (28,48) and separation factor (10,22). Results from this study revealed that it was difficult to predict the separation factor using the one-component permeation ratio (permselectivity) over the experimental range tested. These separation characteristics could be primarily ascribed to the molecular size and structure of each gas, which likely contributed to steric hindrance or molecular sieving within the membrane pore. In addition, the adsorption affinity of each molecule on the membrane surface acted as a key factor in separation performance because it significantly influenced surface diffusion. The generalized Maxwell-Stefan model incorporating the dust gas model, and the Langmuir model could successfully predict the transient and steady-state permeation/separation. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Modeling l-dopa purification by chiral ligand-exchange chromatographyAICHE JOURNAL, Issue 3 2007Nooshafarin Sanaie Abstract A model describing elution-band profiles that combines multiple chemical equilibria theory with the nonideal equilibrium,dispersion equation for solute transport is used to predict and characterize the separation of l,d-dopa by chiral ligand-exchange chromatography (CLEC). Formation constants and stoichiometries for all equilibrium complexes formed in the interstitial volume and pore liquid are taken from standard thermodynamic databases and independent potentiometric titration experiments. Formation constants for complexes formed with the stationary phase ligand (N-octyl-3-octylthio-d-valine) are determined from potentiometric titration data for a water-soluble analogue of the ligand. This set of pure thermodynamic parameters is used to calculate the spatially discretized composition of each column volume element as a function of time. The model includes a temperature-dependent pure-component parameter, determined by regression to a single elution band for the pure component, that corrects for subtle effects associated with immobilizing the N-octyl-3-octylthio-d-valine ligand onto the stationary phase. The model is shown to accurately predict elution chromatograms and separation performance as a function of key column operating variables. The model is then used to better understand the connection between chemical equilibria within the system and changes in band profiles and band separation resulting from changes in column operating conditions. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] CO2 Plasticization of polyethersulfone/polyimide gas-separation membranesAICHE JOURNAL, Issue 7 2003G. C. Kapantaidakis This work reports the CO2 plasticization of gas-separation hollow-fiber membranes based on polyimide and polyethersulfone blends. The feed pressure effect on the permeance of pure gases (CO2, N2) and the separation performance of a gaseous mixture (CO2/N2, 55/45%) is examined. Contrary to dense membranes, the permeance of CO2 through ultrathin asymmetric fibers increases immediately with pressure resulting in pronounced apparent plasticization and reduction of the ideal CO2/N2 selectivity. However, no evidence of plasticization was observed when a CO2/N2, 55/45% mixture was fed to the hollow-fiber membranes. In all cases, CO2 permeance decreased with pressure, while that of N2 remained constant. Experimental results were validated by means of mathematical modeling. Membrane-separation performance was overestimated when pressure-independent permeabilities were used in the model, while pressure-dependent permeabilities, due to the overall effect of plasticization and competition phenomena, explained excellently, the obtained stage-cut and permeate purity. [source] Linearized transport model for nanofiltration: Development and assessmentAICHE JOURNAL, Issue 4 2002W. Richard Bowen Finite difference linearization of pore concentration gradient in nanofiltration membranes greatly simplifies the solution of a three-parameter model (pore radius, membrane charge, and pore dielectric constant) for electrolyte rejection by removing the requirement for numerical integration of the extended Nernst,Planck equation. The validity of the linearized model is first experimentally tested by comparing with a rigorous characterization of the Desal-DK nanofiltration membrane, the linearized model closely agreeing with the numerical solution of the full model. Investigation of pore concentration profiles showed the assumption of linearity to be valid over a wide range of nanofiltration conditions. The linearized model was also successfully extended to ternary electrolyte mixtures, highlighting its main advantage over analytic solutions. Overall, the model is a powerful tool for characterization of nanofiltration membranes and subsequent prediction of separation performance. Computational demands are modest in terms of time and complexity. [source] Boron-substituted ZSM-5 membranes: Preparation and separation performanceAICHE JOURNAL, Issue 6 2000Vu A. Tuan ZSM-5 zeolite membranes with boron substituted into the framework for silicon were prepared on porous stainless-steel and ,-alumina tubular supports. These membranes had higher n-C4H10/i-C4H10 separation selectivities, and effectively separated these isomer mixtures to higher temperatures than membranes with aluminum substituted into the framework. Membranes were prepared with Si/B ratios as low as 12, and the best membranes were prepared from alkali-free gels. The highest n-C4H10/i-C4H10 permselectivity at 473 K was 60, and the highest at 527 K was 24. For most alkali-free membranes, the n-C4H10/i-C4H10 permselectivities and separation selectivities increased with boron content, and membranes on ,-alumina supports had both higher permeances and separation selectivities. Membranes with the same permeances and selectivities can be reproducibly prepared, and they are stable at elevated temperatures. [source] Linear peak capacity of a comprehensive multi-dimensional separationJOURNAL OF SEPARATION SCIENCE, JSS, Issue 19 2008Leonid M. Blumberg Abstract In order to resolve (quantifiably and identifiably separate) the same number of peaks in the analysis of the same mixture yielding statistically uniform peak distribution, a comprehensive 2-D separation needs a two times larger peak capacity than a 1-D separation does. Each additional dimension further reduces the utilization of the peak capacity of comprehensive multi-dimensional (MD) separation by a factor of two per dimension. As a result, the same peak capacity means different things for separations with different dimensionalities. This complicates the use of the peak capacity for comparison of the potential separation performance of the separations with different dimensionalities. To facilitate the comparison, a concept of a linear peak capacity has been proposed. The linear peak capacity of an MD separation is the peak capacity of a 1-D separation that, in the analysis of the same mixture, is statistically expected to resolve the same number of peaks as the MD separation is. There are other factors that differently affect the performance of the separations that have different dimensionalities. Peak capacity of a 2-D separation with a rectangular separation space is 27% larger than the product of the peak capacities of its first and second dimension. This advantage of a 2-D separation is essentially nullified by the fact that the peak capacity of the first dimension of an optimized 2-D separation cannot be higher than 80% of the peak capacity of its first dimension standing alone. All in all, the incremental peak capacity gained from addition of a second dimension will not exceed 50% of the peak capacity of the added second dimension. All results are valid for arbitrarily shaped (not necessarily Gaussian) peaks. [source] Separation of VOCs from N2 using poly(ether block amide) membranesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009Li Liu Abstract This work deals with the separation of volatile organic compounds (VOCs) from nitrogen streams for organic vapour emission control by poly(ether block amide) membranes. As representative air pollutant VOCs, n -pentane, n -hexane, cyclohexane, n -heptane, methanol, ethanol, n -propanol, n -butanol, acetone, dimethyl carbonate, and methyl tert -butyl ether were used in this study. The separation of both binary VOC/N2 and multicomponent VOCs/N2 gas mixtures was carried out, and the membranes exhibited good separation performance. A VOC concentration of more than 90 mol% was achieved at a feed VOC concentration of 5 mol%. It was found that the permeances of the VOCs were mainly dominated by their solubilities in the membrane, whereas the permeance of N2 was affected by the presence of the VOCs. The permeance of N2 in the VOC/N2 mixtures was shown to be higher than pure N2 permeance due to membrane swelling induced by the VOCs dissolved in the membrane. Nevertheless, theVOC/N2 selectivity increased with an increase in the feed VOC concentration. Among the VOCs studied, the membrane showed a higher permeance to alcohol VOCs than paraffin VOCs. The effects of feed VOC concentration, temperature, stage cut, and permeate pressure on the separation performance were investigated. Ce travail porte sur la séparation des composés organiques volatils (COV) présents dans des courants d'azote pour le contrôle des émissions de vapeur organique par des membranes de poly(éther amide bloc). Comme polluants atmosphériques représentatifs des COV, on a utilisé dans cette étude le n-pentane, le n-hexane, le cyclohexane, le n-heptane, le méthanol, l'éthanol, le n-propanol, le n-butanol, l'acétone, le carbonate de diméthyle et le méthyl tertio-butyl. On a procédé à la séparation du mélange de gaz de COV/N2 binaire et du mélange de gaz multicomposant COV/N2, et les membranes montrent une bonne performance de séparation. Une concentration de COV de plus de 90% en poids moléculaire a été obtenue à une concentration d'alimentation de COV de 5% en poids moléculaire. On a trouvé que les perméances de N2 était sensibles à la présence de COV. La perméance de N2 dans les mélanges de COV/N2 s'avère plus élevée que la perméance du N2 pur en raison du gonflement de la membrane provoqué par les COV dissous dans la membrane. Néanmoins, la sélectivité des COV/N2 augmente avec la concentration de COV d'alimentation. Parmi les COV étudiés, la membrane montre la plus haute perméance aux COV d'alcool qu'aux COVde paraffine. Les effets de la concentration de COV d'alimentation, de la température, la coupure de phase et la pression des perméats ont été étudiés. [source] Total analysis of endocrine disruptors in a microchip with gold nanoparticlesELECTROPHORESIS, Issue 18 2010Hui-Bog Noh Abstract The development of a simple, sensitive, and direct method for the total analysis of certain endocrine disruptors was performed by integrating preconcentration steps to a separation step on a microchip through the modification of the field-amplified sample stacking and field-amplified sample injection steps. To improve the preconcentration and separation performances, the preconcentration and separation buffers were modified with citrate-stabilized gold nanoparticles (AuNPs). For the detection of the separated samples, cellulose-dsDNA/AuNPs-modified carbon paste electrodes were used at the channel end. The experimental parameters affecting the analytical performances, such as the buffer concentration, water plug length, SDS concentration in the separation buffer, AuNPs concentration, preconcentration time, detection potential and electrode to channel distance, were examined. The detection limits of the test compounds were between 7.1 and 11.1,fM and that for 4-pentylphenol was 7.1 (±1.1) fM. Dynamic ranges were in the range from 0.15 to 600.0,pM. The experiments with real samples were performed to evaluate the reliability of the proposed method. [source] Analyses of preservatives by capillary electrochromatography using methacrylate ester-based monolithic columnsELECTROPHORESIS, Issue 18-19 2004Hsi-Ya Huang Abstract Five common food preservatives were analyzed by capillary electrochromatography, utilizing a methacrylate ester-based monolithic capillary as separation column. In order to optimize the separation of these preservatives, the effects of the pore size of the polymeric stationary phase, the pH and composition of the mobile phase on separation were examined. For all analytes, it was found that an increase in pore size caused a reduction in retention time. However, separation performances were greatly improved in monolithic columns with smaller pore sizes. The pH of the mobile phase had little influence on separation resolution, but a dramatic effect on the amount of sample that was needed to be electrokinetically injected into the monolithic column. In addition, the retention behaviors of these analytes were strongly influenced by the level of acetonitrile in the mobile phase. An optimal separation of the five preservatives was obtained within 7.0 min with a pH 3.0 mobile phase composed of phosphate buffer and acetonitrile 35:65 v/v. Finally, preservatives in real commercial products, including cold syrup, lotion, wine, and soy sauces, were successfully determined by the methacrylate ester-based polymeric monolithic column under this optimized condition. [source] | ||||||||||