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Coy S.L.,Sionex Corporation | Krylov E.V.,Sionex Corporation | Schneider B.B.,AB SCIEX | Covey T.R.,AB SCIEX | And 6 more authors.
International Journal of Mass Spectrometry | Year: 2010

Technology to enable rapid screening for radiation exposure has been identified as an important need, and, as a part of a NIH/NIAD effort in this direction, metabolomic biomarkers for radiation exposure have been identified in a recent series of papers. To reduce the time necessary to detect and measure these biomarkers, differential mobility spectrometry-mass spectrometry (DMS-MS) systems have been developed and tested. Differential mobility ion filters preselect specific ions and also suppress chemical noise created in typical atmospheric-pressure ionization sources (ESI, MALDI, and others). Differential-mobility-based ion selection is based on the field dependence of ion mobility, which, in turn, depends on ion characteristics that include conformation, charge distribution, molecular polarizability, and other properties, and on the transport gas composition which can be modified to enhance resolution. DMS-MS is able to resolve small-molecule biomarkers from isobaric interferences, and suppresses chemical noise generated in the ion source and in the mass spectrometer, improving selectivity and quantitative accuracy. Our planar DMS design is rapid, operating in a few milliseconds, and analyzes ions before fragmentation. Depending on MS inlet conditions, DMS-selected ions can be dissociated in the MS inlet expansion, before mass analysis, providing a capability similar to MS/MS with simpler instrumentation. This report presents selected DMS-MS experimental results, including resolution of complex test mixtures of isobaric compounds, separation of charge states, separation of isobaric biomarkers (citrate and isocitrate), and separation of nearly isobaric biomarker anions in direct analysis of a bio-fluid sample from the radiation-treated group of a mouse-model study. These uses of DMS combined with moderate resolution MS instrumentation indicate the feasibility of field-deployable instrumentation for biomarker evaluation. © 2010 Elsevier B.V. All rights reserved.

Schneider B.B.,MDS Analytical Technologies | Covey T.R.,MDS Analytical Technologies | Coy S.L.,Sionex Corporation | Krylov E.V.,Sionex Corporation | Nazarov E.G.,Sionex Corporation
European Journal of Mass Spectrometry | Year: 2010

Differential mobility spectrometry (DMS) separates ions on the basis of the difference in their migration rates under high versus low electric fields. Several models describing the physical nature of this field mobility dependence have been proposed but emerging as a dominant effect is the clusterization model sometimes referred to as the dynamic cluster-decluster model. DMS resolution and peak capacity is strongly influenced by the addition of modifiers which results in the formation and dissociation of clusters. This process increases selectivity due to the unique chemical interactions that occur between an ion and neutral gas-phase molecules. It is thus imperative to bring the parameters influencing the chemical interactions under control and find ways to exploit them in order to improve the analytical utility of the device. In this paper, we describe three important areas that need consideration in order to stabilize and capitalize on the chemical processes that dominate a DMS separation. The first involves means of controlling the dynamic equilibrium of the clustering reactions with high concentrations of specific reagents. The second area involves a means to deal with the unwanted heterogeneous cluster ion populations emitted from the electrospray ionization process that degrade resolution and sensitivity. The third involves fine control of parameters that affect the fundamental collision processes, temperature and pressure. © IM Publications LLP 2009 All rights reserved.

Manard M.J.,CA Technologies | Trainham R.,CA Technologies | Weeks S.,CA Technologies | Coy S.L.,Sionex Corporation | And 2 more authors.
International Journal of Mass Spectrometry | Year: 2010

The design of a prototype, field-portable mass spectrometer (MS) is described. The MS has been designed with an atmospheric interface in order to couple the system to a commercially available differential mobility spectrometer. The differential mobility spectrometer provides selective injection of trace-level analytes of interest into the inlet of the MS for real-time chemical detection. To accomplish this task, the MS design incorporates the use of an electrodynamic ion funnel to transport the ion beam, generated at atmospheric pressure, to the high-vacuum chamber that houses the mass analyzer. This leads to a design that utilizes two stages of differential pumping to achieve an overall pressure drop from atmosphere (760Torr) to approximately 1×10-5Torr. A mass resolution of 140 (m/z=84) and a limit of detection of approximately 1ppbv have been measured for the system. © 2010 Elsevier B.V.

Schneider B.B.,MDS Analytical Technologies | Covey T.R.,MDS Analytical Technologies | Coy S.L.,Sionex Corporation | Krylov E.V.,Sionex Corporation | Nazarov E.G.,Sionex Corporation
International Journal of Mass Spectrometry | Year: 2010

Ion filters based on planar DMS can be integrated with the inlet configuration of most mass spectrometers, and are able to enhance the quality of mass analysis and quantitative accuracy by reducing chemical noise, and by pre-separating ions of similar mass. This paper is the first in a series of papers describing the optimization of DMS/MS instrumentation. In this paper the important physical parameters of a planar DMS-MS interface including analyzer geometry, analyzer coupling to a mass spectrometer, and transport gas flow control are considered. The goal is to optimize ion transmission and transport efficiency, provide optimal and adjustable resolution, and produce stable operation under conditions of high sample contamination. We discuss the principles of DMS separations and highlight the theoretical underpinnings. The main differences between planar and cylindrical geometries are presented, including a discussion of the advantages and disadvantages of RF ion focusing. In addition, we present a description of optimization of the frequency and amplitude of the DMS fields for resolution and ion transmission, and a discussion of the influence and importance of ion residence time in DMS. We have constructed a mass spectrometer interface for planar geometries that takes advantage of atmospheric pressure gas dynamic principles, rather than ion focusing, to minimize ion losses from diffusion in the analyzer and to maximize total ion transport into the mass spectrometer. A variety of experimental results has been obtained that illustrate the performance of this type of interface, including tests of resistance to high contamination levels, and the separation of stereoisomers. In a subsequent publication the control of the chemical interactions that drive the separation process of a DMS/MS system will be considered. In a third publication we describe novel electronics designed to provide the high voltage asymmetric waveform fields (SV) required for these devices as well as the effects of different waveforms. © 2010 Elsevier B.V.

Krylov E.V.,Sionex Corporation | Coy S.L.,Sionex Corporation | Vandermey J.,MDS Analytical Technologies | Schneider B.B.,MDS Analytical Technologies | And 2 more authors.
Review of Scientific Instruments | Year: 2010

Devices based on differential mobility spectrometry (DMS) are used in a number of ways, including applications as ion prefilters for API-MS systems, as detectors or selectors in hybrid instruments (GC-DMS, DMS-IMS), and in standalone systems for chemical detection and identification. DMS ion separation is based on the relative difference between high field and low field ion mobility known as the alpha dependence, and requires the application of an intense asymmetric electric field known as the DMS separation field, typically in the megahertz frequency range. DMS performance depends on the waveform and on the magnitude of this separation field. In this paper, we analyze the relationship between separation waveform and DMS resolution and consider feasible separation field generators. We examine ideal and practical DMS separation field waveforms and discuss separation field generator circuit types and their implementations. To facilitate optimization of the generator designs, we present a set of relations that connect ion alpha dependence to DMS separation fields. Using these relationships we evaluate the DMS separation power of common generator types as a function of their waveform parameters. Optimal waveforms for the major types of DMS separation generators are determined for ions with various alpha dependences. These calculations are validated by comparison with experimental data. © 2010 American Institute of Physics.

Tadjimukhamedov F.K.,Purdue University | Jackson A.U.,Purdue University | Nazarov E.G.,Sionex Corporation | Ouyang Z.,Purdue University | Cooks R.G.,Purdue University
Journal of the American Society for Mass Spectrometry | Year: 2010

A planar differential mobility spectrometer (DMS) was coupled to a Mini 10 handheld rectilinear ion trap (RIT) mass spectrometer (MS) (total weight 10 kg), and the performance of the instrument was evaluated using illicit drug analysis. Coupling of DMS (which requires a continuous flow of drift gas) with a miniature MS (which operates best using sample introduction via a discontinuous atmospheric pressure interface, DAPI), was achieved with auxiliary pumping using a 5 L/min miniature diaphragm sample pump placed between the two devices. On-line ion mobility filtering showed to be advantageous in reducing the background chemical noise in the analysis of the psychotropic drug diazepam in urine using nanoelectrospray ionization. The combination of a miniature mass spectrometer with simple and rapid gas-phase ion separation by DMS allowed the characteristic fragmentation pattern of diazepam to be distinguished in a simple urine extract at lower limits of detection (50 ng/mL) than that achieved without DMS (200 ng/mL). The additional separation power of DMS facilitated the identification of two drugs of similar molecular weight, morphine (average MW = 285.34) and diazepam (average MW = 284.70), using a miniature mass spectrometer capable of unit resolution. The similarity in the proton affinities of these two compounds resulted in some cross-interference in the MS data due to facile ionization of the neutral form of the compound even when the ionic form had been separated by DMS. © 2010.

Schneider B.B.,MDS Analytical Technologies | Schneider B.B.,Sionex Corporation | Covey T.R.,MDS Analytical Technologies | Covey T.R.,Sionex Corporation | And 6 more authors.
Analytical Chemistry | Year: 2010

In differential mobility spectrometry (also referred to as high-field asymmetric waveform ion mobility spectrometry), ions are separated on the basis of the difference in their mobility under high and low electric fields. The addition of polar modifiers to the gas transporting the ions through a differential mobility spectrometer enhances the formation of clusters in a field-dependent way and thus amplifies the high- and low-field mobility difference, resulting in increased peak capacity and separation power. Observations of the increase in mobility field dependence are consistent with a cluster formation model, also referred to as the dynamic cluster-decluster model. The uniqueness of chemical interactions that occur between an ion and cluster-forming neutrals increases the selectivity of the separation, and the depression of lowfield mobility relative to high-field mobility increases the compensation voltage and peak capacity. The effect of a polar modifier on the peak capacity across a broad range of chemicals has been investigated. We discuss the theoretical underpinnings which explain the observed effects. In contrast to the result with a polar modifier, we find that using mixtures of inert gases as the transport gas improves the resolution by reducing the peak width but has very little effect on the peak capacity or selectivity. The inert gas helium does not cluster and thus does not reduce low-field mobility relative to high-field mobility. The observed changes in the differential mobility a parameter exhibited by different classes of compounds when the transport gas contains a polar modifier or has a significant fraction of inert gas can be explained on the basis of the physical mechanisms involved in the separation processes. © 2010 American Chemical Society.

Krylov E.,Sionex Corporation
International Journal for Ion Mobility Spectrometry | Year: 2012

Differential mobility spectrometer is a powerful tool used for detection, filtration and characterization of ions in gas-phase. DMS instrumentation analytical performance is a matter of importance for practical application. This paper is devoted to the improving of the planar DMS analytical characteristics. The goal is to optimize ion transmission and separation efficiency for the best possible DMS performance, balanced between sensitivity and selectivity. Analytical characteristics of the DMS instrument depend on a number of interrelated parameters. Present paper focuses on the sensor geometry and transport gas flow rate and its influence on the DMS performance. To find optimal sensor design parameters a systematic approach to the DMS performance is provided and evaluated both theoretically and experimentally. To facilitate DMS optimization special criterion quantitatively describing DMS analytical quality is proposed. DMS instrumental parameters maximizing analytical quality are determined. Theoretical analysis is validated by comparison with experimental data. Practical recommendations following from these finding are presented. © 2012 Springer-Verlag.

Roetering S.,University of Applied Sciences of Leipzig | Nazarov E.G.,Sionex Corporation | Borsdorf H.,Helmholtz Center for Environmental Research | Weickhardt C.,University of Applied Sciences of Leipzig
International Journal for Ion Mobility Spectrometry | Year: 2010

The chances to improve the detection of pesticides using differential mobility spectrometry (DMS) with an atmospheric pressure photoionization (APPI) ion source by means of dopants was investigated. The effect of employing benzene, anisole and chlorobenzene as dopants is described regarding sensitivity, limits of detection and peak displacements in the spectra. For typical pesticides an improvement of detection limits up to two orders of magnitude could be determined, while for the peak shift of individual substances no uniform behaviour was observed. Possible mechanisms of action in respect to atmospheric pressure photoionization (APPI) processes are discussed. © 2010 Springer-Verlag.

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