Biomedical subjects

Bradley B Schneider

Publications and source records attributed to Bradley B Schneider.

9 recordsLinked to original sources

PubMed2006

Design considerations for high speed quantitative mass spectrometry with MALDI ionization.

A MALDI ion source on a triple quadrupole mass spectrometer constructed for the purpose of obtaining high speed quantitative measurements on drugs and other low molecular weight compounds is described. Particular attention is given to the ion generation and transport phenomena that affect analysis speed, throughput, and practical instrument robustness. In this regard parameters that affect desorption speed, beam spreading, ion flight times, sensitivity, signal-to-noise, ion fragmentation, sample carry-over, and instrument contamination are examined and experimental results are provided. MALDI and electrospray sensitivity is compared, to provide a practical frame of reference.

Computer Systems↗

PubMed2006

Ion sampling effects under conditions of total solvent consumption.

The motivation of this work was to study some of the properties of nanoelectrospray operation under conditions where the entire sprayed liquid is vaporized and inhaled into the vacuum system. Under these conditions the desolvation requirements, sampling efficiency, concentration versus mass sensitivity, and molar response characteristics of various compounds were studied. The combined efficiency of ion production from solution and transfer into the vacuum system, referred to as sampling efficiency, is presented under various inlet conditions including different flow rates, solution compositions, and compound types. Under ideal solvent conditions the results for favorable compounds show sampling efficiencies of 70-85% at flows in the range of 50-500 nL/min. Efficiencies were lower for aqueous samples and compounds of different structures gave different molar response factors under these high sampling efficiency conditions. The relative molar response factors are presented in terms of those observed with higher flow rate sources which operate at significantly lower sampling efficiencies. In all cases, operating in this flow regime, the ion count rate was directly proportional to the absolute mass of analyte molecules entering the source. The experimental source used to carry out these studies included gas nebulization to stabilize the electrospray process, a heated laminar flow chamber to enhance desolvation and ion production, and various atmosphere-to-vacuum aperture diameters to maximize ion transfer.

Journal Article↗

PubMed2005

High-performance SPME/AP MALDI system for high-throughput sampling and determination of peptides.

This paper presents the performance characteristics for a new multiplexed solid-phase microextraction/atmospheric pressure matrix-assisted laser desorption/ionization (SPME/AP MALDI) source configuration for a hybrid quadrupole-linear ion trap instrument. The results demonstrate that thorough optimization of parameters such as SPME coating material, optics configurations, extraction solvents, and fiber capacity provides dramatic sensitivity improvements (>1000x) over previous reports in the literature. The multiplexed SPME plate is capable of simultaneous extraction from 16 different wells on a multiwell plate, eliminating the need for extensive sample preparation. Subfemtomole sensitivity is demonstrated for peptide standards and protein digests with run-run reproducibility ranging from approximately 13 to 31%. This high-performance SPME/AP MALDI system shows potential for high-throughput extraction from biological samples.

Angiotensin I↗

PubMed2005

Automated nanospray using chip-based emitters for the quantitative analysis of pharmaceutical compounds.

An automated nanospray system based on chip technology (the NanoMate) was successfully interfaced to a modified Particle Discriminator Interface on a triple quadrupole mass spectrometer. A number of the interface parameters were optimized to improve the sampling efficiency for ions from the chip-based system. Analytical performance was assessed using a number of biochemicals as well as via a methodology for a pharmaceutical that passed validation as required by Good Laboratory Practices. Infusion analyses in flow rates <1 microL/min provided advantages in terms of throughput and sample consumption when compared to other methodologies based on liquid chromatography.

Deoxycytidine↗

PubMed2005

AP and vacuum MALDI on a QqLIT instrument.

This article presents a comparative study of the performance, operational, and instrumental characteristics of AP and vacuum MALDI for the analysis of peptides and protein digests. Spectra generated with the two ion sources were surprisingly similar, both qualitatively and quantitatively, with vacuum MALDI generating ion count rates that were approximately a factor of 2 greater than those generated with AP MALDI on this system. Even though the peptide signals were 2X greater with vacuum MALDI, the background intensities also increased by a similar amount, leading to approximately equivalent signal/background ratios for digests and peptide mixtures. The results suggest that when AP MALDI conditions are properly optimized, the sensitivity can approach that of vacuum MALDI. However, AP MALDI performance is critically affected by source gas flows, potentials, and temperature, making it operationally more complex. In addition, evidence is provided for thermal degradation of samples stored on a target plate within a heated AP MALDI ion source. An improved interface for atmosphere to vacuum ion transfer substantially improved these characteristics.

Atmospheric Pressure↗

PubMed2005

Stable gradient nanoflow LC-MS.

This paper demonstrates improved nanoflow LC-MS performance on a QqTOF instrument with the incorporation of a heated nanoflow interface (particle discriminator) and a nebulizer assisted sprayer. It is shown that the nebulizer broadens the usable range of electrospray potentials, simplifying the tuning procedure, particularly for negative mode nanoflow gradients. The improved desolvation capability with the particle discriminator results in signal/noise improvements of approximately 3.5x for negative ion mode samples prepared in predominantly acidified water as well as increased ion current stability. For nanoLC applications, the combined desolvation capabilities of a counter-current gas and heated laminar flow chamber provide reduced background, increased signal stability, reduced background drift, and improved protein sequence coverage when compared with data generated with only a counter-current gas for desolvation. This system is capable of subfemtomole nanoflow LC-MS sensitivity in both positive and negative ion mode across the solvent gradient.

Journal Article↗

PubMed2003

Particle discriminator interface for nanoflow ESI-MS.

An atmosphere to vacuum interface was designed to exploit the different mobility and momentum characteristics of ions, and charged and neutral particles in electrospray ionization-mass spectrometry. The purpose of this device is to transmit with high efficiency the ions created at atmospheric pressure into the mass analyzer and to deflect the large charged and neutral particles prior to entrance into the vacuum system, thereby maintaining system cleanliness and stability. This interface is particularly suitable for low flow rate electrospray ionization-mass spectrometry where the close proximity of the electrospray emitters to the vacuum entrance, and near total consumption of the entire spray, leads to the production of large quantities of non-desolvated droplets and large charged and neutral particles. The improvement involves the application of potential gradients to a particle discriminator space located between the gas restricting ion entrance orifice of the mass spectrometer and the exit of a heated laminar flow chamber to divert large particles from the gas conductance limiting orifice. A counter-current flow of drying gas is used to deflect neutral particles and solvent vapor. Two stages of desolvation are achieved with the combined effects of the curtain gas and heated laminar flow chamber. This enhances the efficiency of desolvation and ion production, and stabilizes the resulting ion current under a wide variety of solvent compositions. In addition, this system eliminates the problems associated with the boiling of solution in nanospray tips when operated in close proximity to a heated mass spectrometer inlet. The particle discriminator interface gives approximately a 2-fold improvement in ion count rates, and a 3-fold improvement in stability (as measured by the signal relative standard deviation).

Algorithms↗

PubMed2002

Multiple sprayer system for high-throughput electrospray ionization mass spectrometry.

A multiple sprayer electrospray ion source for high-throughput analysis is described. The ion source is comprised of multiple electrospray capillaries, each with an ion lens located near the tip. The electric potentials applied to the ion lenses are used to control the sprayers. The use of ion lenses eliminates the need for mechanical blocking devices to selectively enable or disable the sprayers, and results in a less expensive and more reliable set-up. Sprayers can be enabled or disabled within approximately 50-250 ms when the lens potentials are controlled manually. For simultaneous operation of multiple electrospray capillaries, it is advantageous to orient the capillaries so that the spray from each passes directly in front of the entrance aperture of the mass spectrometer.

Journal Article↗

PubMed2002

An atmospheric pressure ion lens that improves nebulizer assisted electrospray ion sources.

An atmospheric pressure ion lens improves the performance and ease of use of a nebulizer assisted electrospray (ion spray) ion source. The lens is comprised of an oblong-shaped stainless steel ring attached to an external high voltage power supply. The lens is located near the tip of the conductive sprayer, and is maintained at a potential less than that of the sprayer. The ion lens improves the shape of the equipotential lines in the vicinity of the sprayer tip. This lens gives approximately a 2-fold reduction in the signal RSD, a 2-fold increase in the ion signal, an increase in the number of multiply charged ions, and a much broader range of usable sprayer positions.

Journal Article↗