Ion−Neutral Potential Models in Atmospheric Pressure Ion Mobility Time-of-Flight Mass Spectrometry IM(tof)MS

Steiner, Wes E.; English, William A.; Hill, Herbert H.

doi:10.1021/jp056158t

Cited by 24 publications

(11 citation statements)

References 25 publications

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“…Mobility in mixtures is predicted by Blanc’s law, and shows that small amounts of polar gases can prevent the expected hard sphere mobility coefficients from being observed. For instance, the comprehensive drift gas IMS results from the Hill group 14 scale for each ion as expected with reduced mass for several drift gases, but not to the full extent predicted for helium, while low pressure, fully-declustered experiments by Bierbaum and Leone 15 do scale as expected, showing the very high mobility in helium of 11.8 cm 2 /V·s for C 6 H 6 + . This polar-nonpolar mixing effect has also been examined for t-C 4 H 9 + in Ref 16 .…”

Section: Resultsmentioning

confidence: 66%

Chemical Effects in the Separation Process of a Differential Mobility/Mass Spectrometer System

Schneider¹,

Covey²,

Coy³

et al. 2010

Anal. Chem.

155

200

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In differential mobility spectrometry (DMS, also referred to as high field asymmetric waveform ion mobility spectrometry, FAIMS), 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 DMS 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 low-field mobility relative to high-field mobility increases the compensation voltage and peak capacity. The effect of polar modifiers 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 from polar modifiers, we find that using mixtures of inert gases as the transport gas improve resolution by reducing peak width but has very little effect on peak capacity or selectivity. Inert gases do not cluster and thus do not reduce low field mobility relative to high-field mobility. The observed changes in the differential mobility α parameter exhibited by different classes of compounds when the transport gas contains polar modifiers or has a significant fraction of inert gas can be explained on the basis of the physical mechanisms involved in the separation processes.

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Section: Resultsmentioning

confidence: 66%

Chemical Effects in the Separation Process of a Differential Mobility/Mass Spectrometer System

Schneider¹,

Covey²,

Coy³

et al. 2010

Anal. Chem.

155

200

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“…It is quite clear that for a monomer and a dimer with the same reduced mass, the monomer has a lower reduced mobility and therefore a larger collision cross section than that of the dimer. It has previously been shown that the motion of ions in nitrogen at 200°C, where cluster formation is minimal [22], can be described by the rigid sphere model [23]. Our experiments were performed at ambient temperature, where the mobility is expected to be influenced by cluster formation, especially with the water ubiquitously present.…”

Section: Resultsmentioning

confidence: 96%

Characterization of proton-bound acetate dimers in ion mobility spectrometry

Pedersen

Lauritsen

Сысоев

et al. 2008

J. Am. Soc. Mass Spectrom.

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Ionized acetates were used as model compounds to describe gas-phase behavior of oxygen containing compounds with respect to their formation of dimers in ion mobility spectrometry (IMS). The ions were created using corona discharge at atmospheric pressure and separated in a drift tube before analysis of the ions by mass spectrometry. At the ambient operational temperature and pressure used in our instrument, all acetates studied formed dimers. Using a homolog series of n-alkyl-acetates, we found that the collision cross section of a dimer was smaller than that of a monomer with the same reduced mass. Our experiments also showed that the reduced mobility of acetate dimers with different functional groups increased in the order n-alkyl :=:; branched chain alkyl zs cyclo alkyl < aromat. For mixed n-alkyl dimers we found that the reduced mobility of acetate dimers having the same number of carbons, for example a dimer of acetyl acetate and hexyl acetate has the same reduced mobility as a dimer composed of two butyl acetates. The fundamental behavior of acetate monomers and dimers described in this paper will assist in a better understanding of the influence of dimer formation in ion mobility spectrometry. on mobility spectrometry (IMS) is a versatile technique that has found widespread application in many areas, such as military and civil security applications, where it has been used to detect chemical warfare agents, explosives, and drugs [1-4]. The major advantages of IMS instruments are their small size, low power consumption, and capability to operate at atmospheric pressure, which makes them highly suited for real time analysis in the field [I, 5]. However, IMS spectra are sensitive toward changes in analytical conditions such as humidity, pressure, temperature, and matrix [6]. This feature makes it difficult to use the instrument for analysis of more than a limited number of prespecified compounds at a time, and reagent gases are often used to simplify the spectra either by suppressing certain ions [7,8] or by selective dimer formation [9].The creation of an IMS spectrum involves gas-phase ionization followed by a separation of the ions based on their mobility in an electrical field at pressures between -10 2 and 10 5 Pa. As a result of the ionization at atmospheric or near atmospheric pressure the ionized sample molecules may undergo several different transAddress reprint requests to Mr. C. S. Pedersen, Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark. E-mail: csp@kemLku.dk formations such as fragmentation, rearrangement, and cluster formation. In particular molecules containing functional oxygen or nitrogen, atoms tend to make clusters with water molecules or other molecules with similar hydrogen bonding capabilities. Since the separation of ions in an IMS experiment depends upon both charge and size, cluster formation has a large influence upon the observed spectra and mobilities. The formation of clusters can be advantageous. For example, a problem with i...

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“…The polarizability of the helium gas molecule leads to a potential that scales with 1/r 4 , where r is the distance between the point charge (ion) and the induced dipole (gas molecule). This means that the measured collision cross section for very small ions is governed mainly by the attractive interaction due to gas polarizability, rather than by the repulsive interaction due to collisions, which is determined by the van der Waals radii of the silver cluster and the He molecule (Tammet 1995;Gilb et al 2002;Steiner et al 2006). The shift in mobility for the first peak was also observed by Weis et al (2002) who measured the first peak at 30.5 A 2 (Z ¡1 D 0.0523 Vs cm ¡2 ) while the calculated theoretically expected value was 20.8 A 2 (Z ¡1 D 0.0357 Vs cm ¡2 ).…”

Section: Results and Discussion Silver Cluster: Identification Of Clumentioning

confidence: 99%

Atomic Cluster Generation with an Atmospheric Pressure Spark Discharge Generator

Maisser

Barmpounis

Attoui

et al. 2015

Aerosol Science and Technology

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A new method for generating metal clusters in the gas phase is described and characterized in this work. The method is based on material evaporation by spark ablation at atmospheric pressure. The characterization of atomic clusters was done by measuring their electrical mobility. The measured mobilities were compared with values found in literature in order to identify the cluster species. We show that silver clusters consisting from one up to 25 atoms can be produced in helium at atmospheric pressure. In addition, the effect of oxygen concentration on the resulting cluster mobility distribution was investigated. Results show that at higher oxygen level, the mobility distribution is dominated by the abundance of stable clusters (i.e., magic number clusters). This can be attributed to an oxidation etching effect.

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Ion−Neutral Potential Models in Atmospheric Pressure Ion Mobility Time-of-Flight Mass Spectrometry IM(tof)MS

Cited by 24 publications

References 25 publications

Chemical Effects in the Separation Process of a Differential Mobility/Mass Spectrometer System

Chemical Effects in the Separation Process of a Differential Mobility/Mass Spectrometer System

Characterization of proton-bound acetate dimers in ion mobility spectrometry

Atomic Cluster Generation with an Atmospheric Pressure Spark Discharge Generator

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