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Mass Spectrometry System (mass + spectrometry_system)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Modification of a commercial electrospray nebulizer for operation in a liquid chromatography/mass spectrometry system at flow rates in the low,µL/min range

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2001
Alain Carrier
A simple and inexpensive approach to convert the electrospray nebulizer of a commercial liquid chromatography/mass spectrometry (LC/MS) system (HP 1100) to accommodate lower flow rates has been proposed and evaluated. This modification consists of simply replacing the nebulizer needle by a commercially available stainless steel needle with a smaller internal diameter. Experiments were conducted in order to optimize operational parameters. Using two different internal diameter needle sizes, flow rates ranging from 1 to 250,µL/min could be accommodated. The modification presented allows an extension of the range of compatible flow rates without major modification of the standard design of the interface. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Parallel SFC/MS-MUX screening to assess enantiomeric purity

CHIRALITY, Issue 8 2008
Derek B. Laskar
Abstract Enantiomeric excess (ee) was evaluated for two internally synthesized compound libraries using a high-throughput automated, intelligent four-channel parallel supercritical fluid chromatography/mass spectrometry system equipped with a multiplexed ion source interface (SFC/MS-MUX). The two libraries contained compounds spanning a wide range of enantiomeric ratios with structurally diverse chemical scaffolds and stereogenic centers. The system analyzed each sample simultaneously against four chiral columns using up to six organic modifiers. Enhancements to our previously published parallel supercritical fluid chromatography/mass spectrometry system were implemented to address the challenges associated with automated trace enantiomer identification and quantitation. A reversal of enantiomer elution order was observed for several samples across multiple CSPs and modifiers. The relationship between elution order and % ee accuracy is presented for compounds exhibiting high, middle and low % ee values. Despite incidences in which the minor enantiomer eluted prior to the major enantiomer with less than baseline resolution, the overall % ee was in agreement with separations in which full baseline resolution was achieved. The methods presented here demonstrate the value and utility of high-throughput ee determinations to support drug discovery and development programs. Chirality, 2008. © 2008 Wiley-Liss, Inc. [source]

Testosterone 1,-hydroxylation by human cytochrome P450 3A4

FEBS JOURNAL, Issue 19 2004
Joel A. Krauser
Human cytochrome P450 3A4 forms a series of minor testosterone hydroxylation products in addition to 6,-hydroxytestosterone, the major product. One of these, formed at the next highest rate after the 6,- and 2,-hydroxy products, was identified as 1,-hydroxytestosterone. This product was characterized from a mixture of testosterone oxidation products using an HPLC-solid phase extraction-cryoprobe NMR/time-of-flight mass spectrometry system, with an estimated total of ,,6 µg of this product. Mass spectrometry established the formula as C19H29O3 (MH+ 305.2080). The 1-position of the added hydroxyl group was established by correlated spectroscopy and heteronuclear spin quantum correlation experiments, and the ,-stereochemistry of the added hydroxyl group was assigned with a nuclear Overhauser correlated spectroscopy experiment (1,-H). Of several human P450s examined, only P450 3A4 formed this product. The product was also formed in human liver microsomes. [source]

Thin-layer chromatography/electrospray ionization triple-quadrupole linear ion trap mass spectrometry system: analysis of rhodamine dyes separated on reversed-phase C8 plates ,

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2005
Michael J. Ford
Abstract The direct analysis of separated rhodamine dyes on reversed-phase C8 thin-layer chromatography plates using a surface sampling/electrospray emitter probe coupled with a triple-quadrupole linear ion trap mass spectrometer is presented. This report represents continuing work to advance the performance metrics and utility of this basic surface sampling electrospray mass spectrometry system for the analysis of thin-layer chromatography plates. Experimental results examining the role of sampling probe spray end configuration on liquid aspiration rate and gas-phase ion signal generated are discussed. The detection figures-of-merit afforded by full-scan, automated product ion and selected reaction monitoring modes of operation were examined. The effect of different eluting solvents on mass spectrum signal levels with the reversed-phase C8 plate was investigated. The combined effect of eluting solvent flow-rate and development lane surface scan rate on preservation of chromatographic resolution was also studied. Analysis of chromatographically separated red pen ink extracts from eight different pens using selected reaction monitoring demonstrated the potential of this surface sampling electrospray mass spectrometry system for targeted compound analysis with real samples. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Direct injection of 96-well organic extracts onto a hydrophilic interaction chromatography/tandem mass spectrometry system using a silica stationary phase and an aqueous/organic mobile phase

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2004
Weng Naidong
First page of article [source]

A new continuous flow isotope ratio mass spectrometry system for the analysis of ,2H, ,17O and ,18O of small (120,,g) water samples in atmospheric applications

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2004
Peter Franz
A new continuous-flow system for the analysis of the complete stable isotopic composition of water vapor has been developed. The sample size is reduced to only 120,,g (,120,nL of liquid substance) of water, yielding precisions of about 0.7, 1.3 and 7, for ,17O, ,18O and ,2H, respectively. The total time for the analysis of a sample is about 150 min including purging times. Oxidized steel surfaces can be a source of memory effects which can be corrected for. The system is predestined for atmospheric applications in the tropopause region, as the sample can be directly introduced into the system from a cryogenic trap. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Isotopic metrology of carbon dioxide.

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2003

We report high-precision isotopic carbon dioxide measurements, made before and after ion source modification to gas isotope ratio mass spectrometry (IRMS) instruments. Measurement protocols were designed to explore the effects of ion source material substitution, source conductance, inlet pressure, electron emission, acceleration potential, and inlet changeover equilibration time. After modification of the IRMS instruments at the National Institute of Standards and Technology (NIST) and the Max-Planck-Institute for Chemistry (MPI-Mainz), immediate changes were observed. At NIST, measurements were no longer sensitive to inlet equilibration times greater than 15,s, and different settings of ion source conductance resulted in ,13C shifts of about 0.04, per 10, measurement difference between sample and reference, a five-fold improvement. No significant changes in machine performance were observed after a month of use. After a year, performance had degraded slightly, but was controlled by ion source cleaning and the use of low-energy ion acceleration to minimize sputtering. At MPI-Mainz, results were very similar. We report cross-contamination coefficients measured since 1996, and discuss the role of adsorption, ion implantation, and sputtering on cross contamination in mass spectrometry systems. We recommend that users of high-precision IRMS instruments test for and minimize the effects described. Published in 2003 by John Wiley & Sons, Ltd. [source]