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Capillary Interface (capillary + interface)
Selected AbstractsDistinguishing N -oxide and hydroxyl compounds: impact of heated capillary/heated ion transfer tube in inducing atmospheric pressure ionization source decompositionsJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2004Dilrukshi M. Peiris Abstract In the pharmaceutical industry, a higher attrition rate during the drug discovery process means a lower drug failure rate in the later stages. This translates into shorter drug development time and reduced cost for bringing a drug to market. Over the past few years, analytical strategies based on liquid chromatography/mass spectrometry (LC/MS) have gone through revolutionary changes and presently accommodate most of the needs of the pharmaceutical industry. Among these LC/MS techniques, collision induced dissociation (CID) or tandem mass spectrometry (MS/MS and MSn) techniques have been widely used to identify unknown compounds and characterize metabolites. MS/MS methods are generally ineffective for distinguishing isomeric compounds such as metabolites involving oxygenation of carbon or nitrogen atoms. Most recently, atmospheric pressure ionization (API) source decomposition methods have been shown to aid in the mass spectral distinction of isomeric oxygenated (N -oxide vs hydroxyl) products/metabolites. In previous studies, experiments were conducted using mass spectrometers equipped with a heated capillary interface between the mass analyzer and the ionization source. In the present study, we investigated the impact of the length of a heated capillary or heated ion transfer tube (a newer version of the heated capillary designed for accommodating orthogonal API source design) in inducing for-API source deoxygenation that allows the distinction of N -oxide from hydroxyl compounds. 8-Hydroxyquinoline (HO-Q), quinoline- N -oxide (Q-NO) and 8-hydroxyquinoline- N -oxide (HO-Q-NO) were used as model compounds on three different mass spectrometers (LCQ Deca, LCQ Advantage and TSQ Quantum). Irrespective of heated capillary or ion transfer tube length, N -oxides from this class of compounds underwent predominantly deoxygenation decomposition under atmospheric pressure chemical ionization conditions and the abundance of the diagnostic [M + H , O]+ ions increased with increasing vaporizer temperature. Furthermore, the results suggest that in API source decompostion methods described in this paper can be conducted using mass spectrometers with non-heated capillary or ion transfer tube API interfaces. Because N-oxides can undergo in-source decomposition and interfere with quantitation experiments, particular attention should be paid when developing API based bioanalytical methods. Copyright © 2004 John Wiley & Sons, Ltd. [source] Microfluidics-based electrospray ionization enhances the intrasource separation of lipid classes and extends identification of individual molecular species through multi-dimensional mass spectrometry: development of an automated high-throughput platform for shotgun lipidomicsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2008Xianlin Han Herein, we exploit the use of microfluidics and optimized Taylor cones for improved intrasource separation/selective ionization of lipid classes during electrospray ionization. Increased differential ionization of multiple phospholipid classes was achieved through microfluidics with chip-based ionization resulting in substantial enhancement of intrasource separation/selective ionization of phospholipid classes in comparison to the conventional ion source. For example, using myocardial lipid extracts, 3-fold improvements in intrasource separation/selective ionization of myocardial phospholipid classes were routinely realized in the negative-ion mode in the absence of LiOH or other basic modifiers in the infused sample solutions. Importantly, the relative ratios of ions corresponding to individual molecular species in each lipid class to a selected internal standard from myocardial extracts were nearly identical between the chip-based interface and the syringe-pump-driven capillary interface. Therefore, quantitation of individual lipid molecular species directly from biological extracts through comparisons with internal standards in each lipid class was readily accomplished with an accuracy and dynamic range nearly identical to those documented using the well-established direct syringe-pump-driven capillary interface. Collectively, the use of microfluidics and robotic sample handling substantially enhances intrasource separation of lipids in comparison to routine capillary interfaces and greatly facilitates the use of multi-dimensional mass spectrometry using shotgun lipidomics, thereby providing an automated and high-throughput platform for global analyses of cellular lipidomes. Copyright © 2008 John Wiley & Sons, Ltd. [source] A projection scheme for incompressible multiphase flow using adaptive Eulerian gridINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2004T. Chen Abstract This paper presents a finite element method for incompressible multiphase flows with capillary interfaces based on a (formally) second-order projection scheme. The discretization is on a fixed Eulerian grid. The fluid phases are identified and advected using a level set function. The grid is temporarily adapted around the interfaces in order to maintain optimal interpolations accounting for the pressure jump and the discontinuity of the normal velocity derivatives. The least-squares method for computing the curvature is used, combined with piecewise linear approximation to the interface. The time integration is based on a formally second order splitting scheme. The convection substep is integrated over an Eulerian grid using an explicit scheme. The remaining generalized Stokes problem is solved by means of a formally second order pressure-stabilized projection scheme. The pressure boundary condition on the free interface is imposed in a strong form (pointwise) at the pressure-computation substep. This allows capturing significant pressure jumps across the interface without creating spurious instabilities. This method is simple and efficient, as demonstrated by the numerical experiments on a wide range of free-surface problems. Copyright © 2004 John Wiley & Sons, Ltd. [source] Microfluidics-based electrospray ionization enhances the intrasource separation of lipid classes and extends identification of individual molecular species through multi-dimensional mass spectrometry: development of an automated high-throughput platform for shotgun lipidomicsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2008Xianlin Han Herein, we exploit the use of microfluidics and optimized Taylor cones for improved intrasource separation/selective ionization of lipid classes during electrospray ionization. Increased differential ionization of multiple phospholipid classes was achieved through microfluidics with chip-based ionization resulting in substantial enhancement of intrasource separation/selective ionization of phospholipid classes in comparison to the conventional ion source. For example, using myocardial lipid extracts, 3-fold improvements in intrasource separation/selective ionization of myocardial phospholipid classes were routinely realized in the negative-ion mode in the absence of LiOH or other basic modifiers in the infused sample solutions. Importantly, the relative ratios of ions corresponding to individual molecular species in each lipid class to a selected internal standard from myocardial extracts were nearly identical between the chip-based interface and the syringe-pump-driven capillary interface. Therefore, quantitation of individual lipid molecular species directly from biological extracts through comparisons with internal standards in each lipid class was readily accomplished with an accuracy and dynamic range nearly identical to those documented using the well-established direct syringe-pump-driven capillary interface. Collectively, the use of microfluidics and robotic sample handling substantially enhances intrasource separation of lipids in comparison to routine capillary interfaces and greatly facilitates the use of multi-dimensional mass spectrometry using shotgun lipidomics, thereby providing an automated and high-throughput platform for global analyses of cellular lipidomes. Copyright © 2008 John Wiley & Sons, Ltd. [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] | ||||||||||