Radiant energy – Ionic separation or analysis – Ion beam pulsing means with detector synchronizing means
Reexamination Certificate
2000-03-02
2001-05-29
Berman, Jack (Department: 2881)
Radiant energy
Ionic separation or analysis
Ion beam pulsing means with detector synchronizing means
C250S282000
Reexamination Certificate
active
06239428
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to ion mobility spectrometers and methods.
BACKGROUND OF THE INVENTION
Ion mobility spectrometers are commonly used to detect the presence of target compounds. Typically, in an ion mobility spectrometer a target compound is ionized, passed through an electric field and then detected by an electrode detector.
The target compound can be directly ionized by an ionization source that emits energy that interacts with and ionizes the target compound. Alternatively or additionally, the target compound can be indirectly ionized by an ionization source which emits energy that interacts with and ionizes an intermediate compound which, in turn, interacts with and ionizes the target compound.
The amount of time it takes for the ionized target compound to pass through the electric field and reach the electrode detector can depend on a number of parameters, including the mass of the ionized target compound, the charge of the ionized target compound, and the strength of the electric field. By manipulating these parameters, the ionized target compound can be detected by measuring the ion current at the electrode detector at a predetermined time.
One type of ion mobility spectrometer is based on proton transfer. In this type of spectrometer, an ionized intermediate compound transfers a proton to the target compound to form the ionized target compound, which is then passed through an electric field and detected. Generally, the proton affinity of the intermediate compound is less than the proton affinity of the target compound.
Another type of ion mobility spectrometer is based on electron transfer. In this type of spectrometer, an ionized intermediate compound transfers an electron to the target compound to form the ionized target compound, which is then passed through an electric field and detected. Usually, the ionization potential of the intermediate compound is greater than the ionization potential of the target compound.
SUMMARY
In one aspect, the invention features a method of detecting a target compound in a sample. The method includes subjecting the sample to conditions sufficient to ionize the target compound by proton transfer ionization, and subjecting the sample to conditions sufficient to ionize the target compound by electron transfer ionization. The method also includes detecting the proton transfer first ionized sample by ion mobility spectrometry, and detecting the electron transfer ionized sample by ion mobility spectrometry.
Embodiments can include one or more of the following features.
The method can include comparing the detection of the proton transfer ionized sample and the detection of the electron transfer ionized sample. In some embodiments, the method includes determining the presence of the target compound by detection of the compound by both proton transfer ionization and electron transfer ionization.
The sample can be obtained by vapor collection.
The target compound can have a proton affinity of about 7.5 eV or greater and/or an ionization potential of about 10 eV or less. For example, the target compound can have a proton affinity of from about 9 eV to about 12 eV and/or an ionization potential of from about 5 eV to about 8 eV. In some embodiments, the target compound can be an organo-nitrogen compound. In certain embodiments, the target compound is at least one of LSD, heroin, cocaine, or their derivatives.
The proton transfer ionization can include forming a first ionized intermediate compound capable of transferring a proton from the first ionized intermediate compound to the target compound.
The electron transfer ionization can include forming a second ionized intermediate compound capable of transferring an electron from the second ionized intermediate compound to the target compound.
The method can include using a first and/or second intermediate compound. The first intermediate compound can be capable of ionizing a first set of compounds including the target compound and other known compounds, and the second intermediate compound can be capable of ionizing a second set of compounds including the target compound and other known compounds, which can be different than the first set. The first intermediate compound can be an amine, such as a primary amine. The second intermediate compound can be an aromatic compound and/or a compound containing a benzene ring.
The proton transfer and electron transfer ionizations can be detected simultaneously, or the proton transfer and electron transfer ionizations can be detected in series.
In another aspect, the invention features a system capable of detecting a target compound. The system includes a proton transfer ionization source capable of ionizing a first intermediate compound to form a first ionized intermediate compound, an electron transfer ionization source capable of ionizing a second intermediate compound to form a second ionized intermediate compound, and a detector capable of detecting the target compound after ionization by electron transfer or proton transfer. The first intermediate compound can have a lower proton affinity than the target compound, and the second intermediate compound can have a higher ionization potential than the target compound.
Embodiments can have one or more of the following features.
The detector can be an ion mobility spectrometer. The detector can be two ion mobility spectrometers operating in parallel. The detector can be a single ion mobility spectrometer for alternately detecting the proton transfer source and the electron transfer source.
The system can further include a comparison apparatus in electrical communication with the detector. The comparison apparatus can compare a first signal from ionization by proton transfer ionization with a second signal from ionization by electron transfer ionization. The comparison apparatus can determine the presence of the target compound by detection of the compound in both the first and second signals.
The first ionization source can emit electrons capable of ionizing the first intermediate compound to form the first ionized intermediate compound. The second ionization source can be a laser, such as a laser that can emit photons having a wavelength of at least about 190 nanometers, a microchip UV laser, and/or a tunable laser.
The target compound can have a proton affinity of about 7.5 eV or greater and/or an ionization potential of about 10 eV or less. For example, the target compound can have a proton affinity of from about 9 eV to about 12 eV and/or an ionization potential of from about 5 eV to about 8 eV. In some embodiments, the target compound can be an organo-nitrogen compound. In certain embodiments, the target compound is at least one of LSD, heroin, cocaine, or their derivatives.
In a further embodiment, the invention features a system for detecting a target compound in a sample that includes a sample inlet, a first ionization source that can emit electrons capable of ionizing a first intermediate compound to form a first ionized intermediate compound, a laser that can emit photons capable of ionizing a second intermediate compound to form a second ionized intermediate compound, a detector that includes an ion mobility spectrometer capable of detecting the first ionized target compound and the second ionized target compound, and a comparison apparatus in electrical communication with the detector so that the comparison apparatus can compare a first signal corresponding to the first ionized target compound and a second signal corresponding to the second ionized target compound. The first intermediate compound can have a lower proton affinity than the target compound, and the target compound can have a proton affinity of about 7.5 eV or greater. The ionization potential of the second intermediate compound can be greater than an ionization potential of the target compound, and the target compound can have an ionization potential of about 10 eV or less.
Embodiments can have one or more of the following features.
The photons can have a wavelength of at least about 190 nanometers.
The las
Berman Jack
Fish & Richardson P.C.
Massachusetts Institute of Technology
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