Radiant energy – Ionic separation or analysis – Methods
Reexamination Certificate
2001-05-09
2004-12-14
Lee, John D. (Department: 2881)
Radiant energy
Ionic separation or analysis
Methods
C250S281000
Reexamination Certificate
active
06831271
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for separating and enriching isotopes in gaseous phase based on the principle of high field asymmetric waveform ion mobility spectrometry.
BACKGROUND OF THE INVENTION
High sensitivity and amenability to miniaturization for field-portable applications have helped to make ion mobility spectrometry an important technique for the detection of many compounds, including narcotics, explosives, and chemical warfare agents (see, for example, G. Eiceman and Z. Karpas,
Ion Mobility Spectrometry
(CRC. Boca Raton, Fla. 1994); and
Plasma Chromatography
, edited by T. W. Carr (Plenum, New York, 1984)). In ion mobility spectrometry, gas-phase ion mobilities are determined using a drift tube with a constant electric field. Ions are gated into the drift tube and are subsequently separated based upon differences in their drift velocity. The ion drift velocity is proportional to the electric field strength at low electric fields (e.g., 200 V/cm) and the mobility, K, which is determined from experimentation, is independent of the applied field. At high electric fields (e.g. 5000 or 10000 V/cm), the ion drift velocity may no longer be directly proportional to the applied field, and K becomes dependent upon the applied electric field (see G. Eiceman and Z. Karpas,
Ion Mobility Spectrometry
(CRC. Boca Raton, Fla. 1994); and E. A. Mason and E. W. McDaniel,
Transport Properties of Ions in Gases
(Wiley, New York, 1988)). At high electric fields, K is better represented by K
h
, a non-constant high field mobility term. The dependence of K
h
on the applied electric field has been the basis for the development of high field asymmetric waveform ion mobility spectrometry (FAIMS), a term used by the inventors throughout this disclosure, and also referred to as transverse field compensation ion mobility spectrometry, or field ion spectrometry (see I. Buryakov, E. Krylov, E. Nazarov, and U. Rasulev, Int. J. Mass Spectrom. Ion Proc. 128. 143 (1993); D. Riegner, C. Harden, B. Carnahan, and S. Day, Proceedings of the 45th ASMS Conference on Mass Spectrometry and Allied Topics, Palm Springs, Calif., 1-5 Jun. 1997, p. 473; B. Carnahan, S. Day, V. Kouznetsov, M. Matyjaszczyk, and A. Tarassov, Proceedings of the 41st ISA Analysis Division Symposium, Framingham, Mass., 21-24 Apr. 1996, p. 85; and B. Carnahan and A. Tarassov, U.S. Pat. No. 5,420,424). Ions are separated in FAIMS on the basis of the difference in the mobility of an ion at high field K
h
relative to its mobility at low field K. That is, the ions are separated because of the compound dependent behaviour of K
h
as a function of the electric field. This offers a new tool for atmospheric pressure gas-phase ion studies since it is the change in ion mobility and not the absolute ion mobility that is being monitored.
An instrument based on the FAIMS concept has been designed and built by Mine Safety Appliances Company of Pittsburgh, Pa. (“MSA”) for use in trace gas analysis. The MSA instrument is described in U.S. Pat. No. 5,420,424 and is available under the trade mark FIS (for Field Ion Spectrometer). While the use of the MSA instrument (and similar Instruments based on the FAIMS concept) for trace gas analysis is known, the inventors believe that they have identified certain heretofore unrealized properties of these instruments which make them more versatile. Based this realization the inventors have developed what is believed to be a previously unknown method for separation of isotopes of ions. A summary and detailed description of the present invention is provided below.
SUMMARY OF THE INVENTION
The present invention provides a method for identifying isotopes, comprising the steps of:
a) providing at least one ionization source for providing ions at least some of which are isotopes;
b) providing an analyzer region defined by a space between at least first and second spaced apart electrodes, said analyzer region being in communication with at least one of each of a gas inlet, a gas outlet, an ion inlet and an ion outlet, and introducing said ions into said analyzer region through said ion inlet;
c) applying an asymmetric waveform voltage and a direct current compensation voltage to at least one of said electrodes;
d) setting said asymmetric waveform voltage;
e) varying said direct current compensation voltage and measuring resulting transmitted ions at said ion outlet, so as to produce a compensation voltage scan for said transmitted ions;
f) identifying peaks in said compensation voltage scan corresponding to said isotopes; and
g) setting said direct current compensation voltage to correspond to one of said peaks, so as to separate and enrich a desired isotope.
Advantageously, the method is operable substantially at atmospheric pressure and substantially at room temperature.
The method may further include the step of detecting said transmitted ions by mass spectrometry.
Such transmitted ions may be subjected to a mass analysis scan to provide ion intensity data over a selected range of mass to charge ratios.
Typically, the method includes providing a gas flow through said analyzer region, so as to transport said ions along said analyzer region, although it will be understood that other ion transport means are possible.
Furthermore, in identifying a peak, it will be understood that the term peak is not limited to the apex of the peak, and at a peak will typically have a noticeable width, or a compensation voltage range in which the peak appears.
Finally, it will be understood that while mass spectrometry may be used for the purpose of compensation voltage scans, mass spectrometry is not necessary once the operating conditions have been determined. That is to say, isotopes separated and enriched by the above method may be collected for further processing.
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Buryakov, I. A., Krylov, E. V., Nazarov, E. G., and Rasulev, U. K., A new method of separation of multi-atomic ions by mobility at atmospheric pressure using a high-frequency amplitude-symmetric strong electric field, Int. J. Mass Spectrom. Ion Processes, 128, 143 (1993).
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Carnahan, B., Day, S., Kouznetsov, V., Matyjaszczyk, M., and Tarassov, A., Filed Ion Spectrometry—A New Analytical Technology for Trace Gas Analysis Proceedings of the 41st Annual ISA Analysis Division Symposium, , Framingham, MA, pp. 85 (1996).
Riegner, D. E., Harden, C. S., Carnahan, B., and Day, S., Qualitative Evaluation of Field Ion Spectrometry for Chemical Warfare Agent Detection Proceedings of the 45th ASMS Conference on Mass Spectrometry and Allied Topics, , Palm Springs, California, pp. 473 (1997).
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Barnett David
Guevremont Roger
Purves Randy
Freedman & Associates
Gurzo Paul M.
Lee John D.
National Research Council Canada
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