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Dead Volume (dead + volume)
Selected AbstractsCEC-ESI ion trap MS of multiple drugs of abuseELECTROPHORESIS, Issue 7 2010Zeineb 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 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] Sequencing of real-world samples using a microfabricated hybrid device having unconstrained straight separation channelsELECTROPHORESIS, Issue 21 2003Shaorong Liu Abstract We describe a microfabricated hybrid device that consists of a microfabricated chip containing multiple twin-T injectors attached to an array of capillaries that serve as the separation channels. A new fabrication process was employed to create two differently sized round channels in a chip. Twin-T injectors were formed by the smaller round channels that match the bore of the separation capillaries and separation capillaries were incorporated to the injectors through the larger round channels that match the outer diameter of the capillaries. This allows for a minimum dead volume and provides a robust chip/capillary interface. This hybrid design takes full advantage, such as sample stacking and purification and uniform signal intensity profile, of the unique chip injection scheme for DNA sequencing while employing long straight capillaries for the separations. In essence, the separation channel length is optimized for both speed and resolution since it is unconstrained by chip size. To demonstrate the reliability and practicality of this hybrid device, we sequenced over 1000 real-world samples from Human Chromosome 5 and Ciona intestinalis, prepared at Joint Genome Institute. We achieved average Phred20 read of 675 bases in about 70 min with a success rate of 91%. For the similar type of samples on MegaBACE 1000, the average Phred20 read is about 550,600 bases in 120 min separation time with a success rate of about 80,90%. [source] Simultaneous estimation of diffusive Volatile Organic Compound (VOC) fluxes and Non-Aqueous Phase Liquid (NAPL) saturation in the vadose zoneGROUND WATER MONITORING & REMEDIATION, Issue 2 2005David Werner Soil-gas monitoring is a widely used tool to observe the migration of volatile organic compounds (VOCs) at contaminated sites. By combining this technique with natural gradient tracer methods, diffusive contaminant fluxes can be measured in situ, and non,aqueous phase liquid (NAPL) can be detected and roughly quantified. This work describes the new approach and its application at a field site in Denmark with an emplaced NAPL contamination. Soil-gas probes with a low dead volume were installed at 1-m depths in the sandy vadose zone, and a small volume of gas containing conservative and partitioning tracers was injected. Soil-gas samples were withdrawn subsequently during 1 to 4 h and analyzed simultaneously for VOCs and tracers. Tracers detected the NAPL reliably, and the combined data allowed for a close delineation of the source zone. The calculated NAPL saturation deviated by up to a factor of 3 from the analyses of soil cores. Better agreement was found by taking the NAPL composition into consideration, which is, however, generally unknown at the actual field sites. In addition, the tracers were also used to estimate effective diffusion coefficients in situ, which varied by a factor of 2 between various locations. From these data, diffusive contaminant vapor fluxes were quantified without additional laboratory experiments or the use of empirical relationships. The new approach yields a better site investigation with a few additional measurements. [source] Tapered element oscillating microbalance (TEOM) studies of isobutane, n-butane and propane sorption in ,- and Y-zeolitesAICHE JOURNAL, Issue 5 2010Kening Gong Abstract A TEOM is used to elucidate the adsorption/desorption characteristics of alkylation reactants on USY- and ,-zeolites. Equilibrium adsorption isotherms were obtained on USY- and ,-zeolites using n-butane, isobutane and propane as proxy reactant molecules (T = 303,398 K, adsorbate partial pressure 0,1.2 bar). Analysis of the transient adsorption/desorption profiles of these molecules from either a bed of the zeolite or pelletized particles of the crystals (with mean size < 1 ,m) demonstrate that diffusion in the secondary meso-/macroporous structure formed in the packing or the pellets controls the overall sorption rates. The experimental adsorption/desorption profiles from the pelletized zeolites were regressed with available mathematical models to obtain effective meso-/macropore diffusivities for reactant molecules, and nearly perfect fits of the experimental and the modeled profiles. Taking into account the dead volume in the system, a criterion for reliable measurements of either micropore or mesopore diffusivities by the TEOM technique is derived. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Separation of benzene and deuterated benzenes by reversed-phase and recycle liquid chromatography using monolithic capillary columnsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 15-16 2004Lee Wah Lim Abstract An alternate pumping-recycle system utilizing a commercially available low dead-volume switching valve was developed for microcolumn LC. The recycle system had two separation columns, and the dead volume of the recycling lines was kept to a minimum by avoiding passage of the sample through the pump chamber, sample injector, and the normal path length of a conventional UV detector. The drawback of the high total back pressure caused by the second column that is placed after the detector was overcome by on-column detection, and this eliminated the need for a high pressure flow cell. The system was used for the separation of an authentic mixture of benzene, benzene-1,3,5-d3, and benzene-d6. Baseline separation was accomplished after six cycles and the calculated theoretical plate number for benzene was 230,000. It was observed that the theoretical plate number (N) increased linearly with increasing number of cycles, and the N per unit time increased with increasing inlet pressure. The separation conditions were optimized and the separation of benzene and benzene-d6 was accomplished within 75 min at 2.5 MPa inlet pressure. [source] Serially coupled microcolumn reversed phase liquid chromatography for shotgun proteomic analysisPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 7 2009Dingyin Tao Abstract Microcolumn RPLC (,RPLC) is one of the optimum separation modes for shotgun proteomic analysis. To identify as many proteins as possible by MS/MS, the improvement on separation efficiency and peak capacity of ,RPLC is indispensable. Although the increase in column length is one of the effective solutions, the preparation of a long microcolumn is rather difficult due to the high backpressure generated during the packing procedure. In our recent work, through connecting microcolumns of 5, 10, and 15,cm length via unions with minimal dead volume, long microcolumns with length up to 30,cm were obtained, with which 318 proteins were identified from proteins extracted from Escherichia coli by ,RPLC-ESI MS/MS, and similar distributions of Mw and pI were found with single and various coupled microcolumns. Furthermore, by using MS/MS with improved sensitivity, with such a serially coupled 30,cm long microcolumn, 1692 proteins were identified within 7,h from rat brain tissue, with false positive rate (FPR) <1%. All these results demonstrated that serially couple microcolumns might be of great promising to improve the separation capacity of ,RPLC in shotgun proteomic analysis. [source] A practical interface for microfluidics and nanoelectrospray mass spectrometryELECTROPHORESIS, Issue 9 2008Sergio L. S. Freire Abstract We report a new method for fabricating nanospray ionization tips for MS, formed from glass substrates and the inert polymer, parylene-C. Using a single photolithography step, the emitters are formed contiguously with microchannels, such that no dead volumes are observed. In addition, because the devices are very thin (,0.3,mm) and the tips are formed at rectangular corners, the Taylor cone volumes are small, which makes the method attractive for future integration with microfluidic separations. Device performance was demonstrated by evaluating diverse analytes, ranging from synthetic polymers, to peptides, to nucleic acids. For all analytes, performance was similar to that of conventional emitters (pulled-glass capillaries and the Agilent HPLC ChipÔ) with the advantage of rapid, batch fabrication of identical devices. [source] Separation of chiral mixtures in real SMB units: The FlexSMB-LSRE®AICHE JOURNAL, Issue 1 2010Pedro Sá Gomes Abstract In this work, a procedure for the separation of a racemic mixture of guaifenesin onto a chiral stationary phase (Chiralpak AD), by means of Simulated Moving Bed (SMB) technology, is presented in four major steps: (1) search for the suitable stationary and mobile phases; (2) determination of sorption parameters and validation by frontal analysis; (3) modeling and design of the SMB unit; and (4) operation and demonstration. A major emphasis is given to the common deviations that "real" SMB units present when compared with the theoretical apparatus (due to tubing and equipment dead volumes, switching time asymmetries and delays, pumps flow rates variations). These deviations are analyzed before and after the design and construction of the FlexSMB-LSRE® unit, a new flexible unit, hereby presented. A detailed model that takes into account tubing and equipment dead volumes, as well as switching time asymmetries and delay, was used to study and compare different dead volumes design and compensating strategies. It is shown that all these approaches can be converged into a switching time compensating strategy. This approach served to predict the experimental operating conditions and run a classical SMB experiment, which afterwards was compared with the simulated profiles obtained for the FlexSMB-LSRE® unit. The result of the separation was guaifenesin enantiomers with purities above 98% and a productivity value of 23 genantiomer/(dm3 CSP day). © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Liquid flow in capillary (electro)chromatography: Generation and control of micro- and nanoliter volumesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2003Erdmann Rapp Abstract We describe and discuss instrumental developments in capillary (electro)chromatography which are of particular relevance for generating (and controlling) required volumetric flow rates in the micro- and nanoliter range through packed capillaries. Both isocratic and gradient elution are considered. For capillary HPLC this practically involves only commercial instrumentation, with systems based on syringe or piston pumps, but it also realizes the innovative concept of a high-pressure electrokinetic pump. The numerous systems that have been used to generate electroosmotic flow through chromatographic beds are classified under the following headings: i) basically commercial capillary electrophoresis instruments (adapted for electrochromatography); ii) home-built configurations; and iii) commercial capillary electrochromatography systems. Concerning the reviewed instrumentation, emphasis is placed on feasibility, automation, as well as system-inherent delay times and dead volumes. [source] | ||||||||||