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Abstract No.: MoP-136
Session: Ion Mobility Mass Spectrometry
Presentation date: Mon, Aug 28, 2006
Presentation time: 14:30 – 16:00

Ion Cooling in Adiabatic Supersonic Gas Flow and Ion Mirror Reflection from Charged Dielectric Films on Conducting Surfaces as a New Way for Inserting Mobility Separated Ions into Orthogonal Injection TOFMS

Valeriy Vladislavovich Raznikov1, Vladislav Valerievich Zelenov1, Elena Viktorovna Aparina1, Sergey Valentinovich Ivashin1, Gennadiy Nikolaevich Savenkov1, Michael Vladimirovich Ugarov2, Agnes Mariemadeleine Tempez2, J. Albert Schultz2

1 Institute for Energy Problems of Chemical Physics, Chernogolovka, Russian Federation
2 Ionwerks,Inc., Houston, United States

Correspondence address: Valeriy Vladislavovich Raznikov, Institute for Energy Problems of Chemical Physics, Russian Academy of Sciences, Prosp. Acad. Semenova, 1/10, Tsentral'naya, 4V-30, Chernogolovka, Moscow region, 142432 Russian Federation.

Keywords: Computer Modeling, Simulation; Ion Cooling; Ion Mirror; Mass Spectrometry, Ion Mobility.

Novel aspect: Found experimentally the divergence of C6Br6 ions in adiabatic helium flow, 0.02 radian, corresponds to the transversal ion temperature ~10K. An ion mirror reflection from dielectrically coated charged conducting surface was confirmed too.

 

Ion transmission and divergence of the ion beam at the entrance of TOFMS are the crucial properties for interfacing a mobility cell with TOFMS. Small apertures with sharp edges are usually used to avoidlarge ion losses during transport from a relatively high pressure region to a lower pressure region. This results in strongly divergent gas flow and increased divergence of the ion beam. Using RF ion guides can reduce this divergence but the temperature of the buffer gas defines the limit. One possible way for decreasing ion divergence in such interfaces is to use an adiabatic supersonic gas flow formed in a cylindrical channel to transport gas and ions from mobility cell.1
In this case the gas flow has energy of atom motion in orthogonal plane close to 1K or less. If ions travel with the cooled gas for a certain time the orthogonal motion energy of ions is reduced. This results in better performance of the orthogonal injection TOFMS. To avoid additional losses of ions inside the cylindrical channel and the decrease of mobility resolution due to the low initial gas flow velocity, this channel may be built as a sequence of insulated conductor rings. A voltage distribution is applied along the channel to provide ion motion with a velocity close to that inside the mobility cell. To completely eliminate the losses of ions inside the channel its internal surface can be coated with a thin dielectric film and charged before the measurements by ions of the same charge sign. Computer simulations show that surfaces charged with sufficient density can reflect low energy ions as a mirror. This approach was tested experimentally. Special experimental setup was constructed to test properties of the interface between ion mobility cell and TOFMS. By measuring average divergence of helium ions (~0.045 radian) traveling with the adiabatic helium flow it was found that the motion of helium atoms in the plane orthogonal to the direction of the flow corresponds to a temperature of about 1K. This value is close to the theoretically predicted one. Average divergence of C6Br6 ions was measured to be ~0.02 radian which corresponds to the transversal temperature of ions of about 10K. To prove the phenomenon of the ion mirror reflection the ion beam was shifted by a pair of parallel flat plates coated and charged in advance. These results confirm theoretical assumptions and the possibility of practical use of this approach for interfacing mobility cell and TOFMS and improving performance of analytical instruments.

1. V. V. Raznikov, V. V. Zelenov, E. V. Aparina, S. V. Ivashin, G. N. Savenkov, M. Ugarov, A. Tempez and J. A. 53rd Conference of American Society of Mass Spectrometry San Antonio, USA (2005).

The work was supported by CRDF, grant #RC1-563-MO-03.