Technispan LLC

Lutherville, MD, United States

Technispan LLC

Lutherville, MD, United States
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Except for electrospray ionization that was introduced later to handle biochemical analyses, the radioactive source has been the benchmark ionization source for ion mobility spectrometry. On the other hand, the licensing requirements accompanying the use of the source has created a desire to replace it with a non-radioactive source with an equivalent ionization capability. Two such sources are the discharge and photo-ionization sources that are capable of negatively ionizing the internally hydrogen bonded ketoB isomer of methyl salicylate. IMMS data show that if the negative reactant ions are NO3− · HNO3 (discharge source) or CO3− (doped photoionization source), methyl salicylate cannot be ionized. However when the sources are synchronously pulsed with a shutter grid, methyl salicylate can be ionized by the formation of the oxygen anion adduct, O2− · M, similar to radioactive ionization. The ionization capability depends not only upon the partial concentration of oxygen in the immediate ionization region but also on the geometry used to construct the source. Molecular modeling shows that the UV radiation emitted by the sources will photodissociate the reactant ions that reconstitute as the energy of the UV radiation decreases during the pulsing cycle. The reconstitution of CO3− is delayed due to a change in geometric symmetry and is the first to leave the ionization region because of its high mobility. This allows methyl salicylate to be ionized by oxygen anions. © 2015, Springer-Verlag Berlin Heidelberg.


Spangler G.E.,Technispan LLC
Analytical Chemistry | Year: 2010

The fundamental transport theory for ion mobility spectrometry is modified to include effects of space charge. The new theory is then applied to describing the performance of "inverse ion mobility spectrometry" recently reported in Tabrizchi, M.; Jazan, E. Anal. Chem. 2010, 82, 746-750 using a discharge ionization source. The improved separation capabilities arise from space charge repulsion of the greater number of ions that are introduced into the drift tube by the technique. A larger effective diffusion coefficient and additional displacement velocities for the leading and trailing edges of the ion mobility peak account for the results. Performance is compared to conventional linear ion mobility spectrometry, with and without a radioactive source for ionization. © 2010 American Chemical Society.


Spangler G.E.,Technispan LLC
International Journal for Ion Mobility Spectrometry | Year: 2012

Using the Langevin equation for ion motion in the presence of a variable electric field, and expressing the collision frequency in a manner that conforms to scattering a polyatomic ion with an equivalent hard-sphere core, a relationship is derived for the compensation and dispersion fields in a differential ion mobility spectrometer (DIMS). For a conservative collision (no clustering or ion-neutral dissociation or rearrangement interactions), the compensation field depends on both even and odd powers of the dispersion field, and the relationship between both fields is independent of pressure when the fields are divided by the drift gas density. Because the first and most important approximation for the compensation field is proportional to the square of ion mobility under zero field conditions, the compensation field increases with the temperature of the drift gas, but the functional form for the temperature dependence involves higher order terms and requires additional knowledge of the temperature dependence for the collision cross section. Duty cycle curves for long-chain secondary ketones compare favorably to experiments using an asymmetric rectangular waveform for excitation. © 2012 Springer-Verlag.


Spangler G.E.,Technispan LLC
International Journal for Ion Mobility Spectrometry | Year: 2013

A classical theory for the collision cross section associated with elastic scattering in ion mobility spectrometry is developed. The collision cross section is found to be equal to a hard-sphere collision cross section evaluated at the turning radius plus a potential scattering term inversely proportional to the effective temperature. The results of the theory are compared to current theories by fitting reduced collision cross sections for both small-ion and large-ion mobility data using a molecular modeled hard-sphere collision cross section as reference. The turning point radius is found to be 0.7 of the hard-sphere collision radius and the interaction potential evaluated at the turning point varies inversely as the square of the turning radius. Taken in combination, classical theory provides an incomplete description of the scattering event. © 2013 Springer-Verlag Berlin Heidelberg.

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