Patent Publication Number: US-2020286723-A1

Title: Apparatus for Detecting Constituents in a Sample and Method of Using the Same

Description:
CROSS REFERENCE 
     The present application is a continuation application of U.S. patent application Ser. No. 16/031,087, entitled “Apparatus for Detecting Constituents in a Sample and Method of Using the Same” and filed on Jul. 10, 2018, which is a continuation of U.S. patent application Ser. No. 15/370,947, of the same title, filed on Dec. 6, 2016, and issued as U.S. Pat. No. 10,049,868 on Aug. 14, 2018, both of which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     The embodiments described herein relate generally to ion mobility spectrometer (IMS) systems and ion trap mobility spectrometer (ITMS) systems and, more particularly, to IMS and ITMS detection systems for enhancing detection of materials of interest through enhanced information of fragmented ions. 
     At least some known spectrometric detection devices include a time-of-flight (TOF) ion mobility spectrometer (IMS) detection system and a TOF ion trap mobility spectrometer (ITMS) detection system. Such TOF-IMS and -ITMS detection systems are used to detect trace amounts of materials of interest, e.g., residues, in the presence of interfering substances in collected samples. In at least some known IMS and ITMS systems, ions are generated in an ionization chamber to increase the ion population therein and a retaining grid or an ion gate is maintained at a potential to induce a retention field and reduce the potential for ion leakage from the chamber. The ions are “pulsed” from the ionization chamber into a drift region through the retaining grid or ion gate. The ions are transported through the drift region to a collector electrode using an electric field. Signals representative of the ion population at the collector electrode are generated and transmitted to an analysis instrument and/or system to determine the constituents in the collected gas samples. Based on an ions&#39; mass, charge, size, and shape, the ion mobility determines the migration time through the drift region which is characteristic of different ions, leading to the ability to distinguish different analyte species. 
     However, many known drift tubes of IMS and ITMS systems have a limited resolving power. As peaks generated by ions from different compounds share similar drift times, some of the interferences, including benign substances, have the same drift times as the analyte compounds of interest associated with an increasing number of threats programmed into the detection library and, therefore, create false alarms. A number of methods and apparatus have been used to characterize the ions of interest and to decrease the false alarm rate which is addressed by the concept of the reactive drift tubes. 
     One method proposed to decrease the false alarm rate is fragmentation, i.e., the dissociation of energetically unstable molecular ions to form ion fragments of a molecule that induce a pattern in the mass spectrum or mobility spectrum used to determine structural information of the original molecule. Fragmentation can be achieved through a variety of means, including fragmentation induced by collision induced dissociation (CID) with selected gases injected into the flow path of the apparatus, fragmentation induced through a set of electrodes capable of generating electric fields with sufficiently high electric field strength to thermally form disassociated products, dissociation through laser that, depending on the required wavelength and molecules to be dissociated, uses one of photodissociation, infrared multiphoton dissociation, and thermal dissociation. Further methods of fragmentation include electron capture and transfer methods through injection of active chemicals. 
     Some known IMS and ITMS systems use ion dissociation through a high-voltage radio-frequency (HV RF) unit positioned within the drift tube. However, such IMS and ITMS systems lack the selection of ions to be fragmented, e.g., through a second ion shutter before the HV-RF unit. Therefore, most of the ions to be fragmented and the fragmented ions enter the second portion of the drift region without any screening, regardless of the chemical makeup of the fragmented ions. As such, the assignment of the fragment ions to spectral patterns is complex with little to no discrimination. The results may be ambiguous because the ability to discern the identity of the resulting fragments is limited since the ions to be dissociated are not separated from the other ions. In some of these known IMS and ITMS systems, operation at reduced pressures is one attempt of reducing the number of ion collisions and thus reducing the number of fragments to generate a more simplistic raw data stream, but the simplicity of the IMS and ITMS techniques is compromised by adding the additional hardware, such as vacuum chambers and pumps. 
     Some other known IMS and ITMS systems include a plurality of tandem drift tubes with ion control grids therebetween, where one of the drift tubes includes a fragmentation device. Such tandem drift tube devices are configured to select ions from a first drift tube through an ion control grid for introduction into a second drift tube for fragmentation through one of laser irradiation and vapor injection to promote selective reactions and additional analytical selectivity. However, such mechanisms substantially form adducts with the selected ions that are transferred to a third drift tube through another ion control grid for characterization therein. Also, uncontrolled movement of sample neutrals between mobility regions facilitates ion molecule reactions in the drift regions that further complicate the interpretation of the resultant spectra. 
     BRIEF DESCRIPTION 
     In one aspect, an apparatus for detecting constituents in a sample is provided. The apparatus includes a first drift tube defining a first drift region, a second drift tube defining a second drift region, and a controllable electric field device coupled to the first drift tube and the second drift tube. The controllable electric field device at least partially defines a fragmentation region. The apparatus also includes a first ion shutter positioned between the first drift region and the fragmentation region. The apparatus also includes a control system coupled to the controllable electric field device and the first ion shutter. The control system is configured to facilitate injection of a selected portion of the predetermined fragmented ions into the second drift region. The control system includes a processor and is also configured to regulate the first ion shutter a first predetermined temporal period, thereby facilitating injection of a selected portion of ions from the first drift region into the fragmentation region. The control system is further configured to regulate the controllable electric field device to modify the selected portion of ions to generate predetermined ion fragments within the fragmentation region. 
     In another aspect, a method of detecting constituents in a sample is provided. The method includes channeling a sample gas stream to be tested for constituents into an ionization region, generating a plurality of ions in the ionization region, and injecting at least a portion of the ions from the ionization region into a first drift region. The method also includes injecting a selected portion of ions from the first drift region into a fragmentation region including regulating a first ion shutter a first predetermined temporal period, where the first ion shutter is positioned between the first drift region and the fragmentation region. The method further includes modifying the selected portion of ions, thereby generating predetermined ion fragments within the fragmentation region including regulating a controllable electric field device positioned within the fragmentation region. 
    
    
     
       DRAWINGS 
         FIGS. 1-4  show exemplary embodiments of the systems and methods described herein. 
         FIG. 1  is a schematic view of an exemplary ion trap mobility spectrometer (ITMS) detection system; 
         FIG. 2  is a schematic view of an alternative ion trap mobility spectrometer (ITMS) detection system; 
         FIG. 3  is a graphical view of exemplary spectra that may be produced using the ITMS detection systems shown in  FIGS. 1 and 2 ; and 
         FIG. 4  is a graphical view of additional exemplary spectra that may be produced using the ITMS detection systems shown in  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments described herein provide a cost-effective system and method for improving detection of materials of interest from an object or person. The systems and methods described herein use a detector having two sequentially arranged drift tubes which are separated by shutters facilitating ions of a user-selected, i.e., library-defined drift time to be introduced into the second drift tube whereas other ions of a different mobility are discarded as needed. The tandem reactive IMS and ITMS devices disclosed herein facilitate multiple opportunities to isolate ions of interest including ion separation and selection in the first drift tube, predetermined modification through fragmentation with a controllable electric field, and selected transmission into the second drift tube ultimately ending with specific identification of the ions. Regulation of the electric field strength and temperature analyte ions from one compound may dissociate and form dissociation products that can further be characterized, while ions from another compound may dissociate as well but form different products or may even not dissociate at all. As such, this dissociation information is important for providing another dimension of characterizing the mobility of ions by their stability and their dissociation products which provides additional confidence in the presence or absence of peaks that facilitates determining if an alarm could be generated or rejected. The results are more easily interpreted and provide more definitive information that can be used for the characterization of ions since only ions of a particular drift time are exposed to the high electric field and the associated fragmentation. Consequently substantially all dissociation products detected in the second drift tube originate from the ions selected from the first drift tube and subsequently fragmented. Moreover, the additional optional introduction of dopants facilitates further modification of the selected ions through chemical reactions with or without dissociation. As such, the systems described herein facilitate an additional level of selectivity that dramatically reduces the false alarm rate from that observed on traditional IMS systems. Therefore, the portable mobility spectrometers described herein facilitate substance analysis with higher confidence while maintaining atmospheric pressure operation. 
       FIG. 1  is a schematic view of an exemplary time-of-flight (TOF) ion trap mobility spectrometer (ITMS) detection system  100  (not drawn to scale). ITMS detection system  100  includes a casing  102 . ITMS detection system  100  also includes a gas inlet tube  104  and a gas outlet tube  106  coupled to casing  102 . In the exemplary embodiment, casing  102  includes an ion trap reactor  108  coupled in flow communication with gas inlet tube  104 . Ion trap reactor  108  includes an ionizing source material (not shown), e.g., and without limitation, nickel-63 ( 63 Ni) that emits low-energy beta-(β-) particles. Alternatively, any ionizing source or ionizing source material that enables operation of ITMS detection system  100  as described herein is used. ITMS detection system  100  further includes a retaining grid  110  extending over an outlet end of ion trap reactor  108 . 
     Casing  102  further defines a tandem reactive dual drift tube and dual shutter configuration  112 . Configuration  112  includes a first drift tube  114  defining a first drift field region  116  coupled in flow communication with ion trap reactor  108 . Configuration  112  further includes a series of sequential annular electrodes E 1 , E 2 , E 3 , E 4 , E 5 , E 6 , and E 7  extending about first drift field region  116 . Configuration  112  also includes a fragmentation region  118  at least partially defined by casing  102 . Fragmentation region  118  facilitates predetermined modifications of ions received from first drift field region  116  through fragmentation with a controllable electric field generated by an electric field generation device  120  that includes a high-voltage radio-frequency (HV RF) unit  122  and electrodes  124  and  126  spaced from each other across the diameter of fragmentation region  118 . Electrodes  124  and  126  are any devices that enable operation of ITMS detection system  100  through production of a strong electric field, such devices including, but not limited to, wire grids and other metal structures that generate sufficient field strength. Electric field generation device  120  generates electric fields of sufficient strengths and frequencies to modify ions therein (discussed further below). 
     Also, in the exemplary embodiment, configuration  112  further includes a first ion shutter  128  that at least partially defines first drift field region  116  and fragmentation region  118  when energized and facilitates flow communication between regions  116  and  118  when de-energized. In addition, configuration  112  includes a second drift tube  130  defining a second drift field region  132 . Configuration  112  also includes a series of sequential annular electrodes E 8 , E 9 , E 10 , E 11 , E 12 , E 13 , and E 14  extending about second drift field region  132 . Second drift field region  132  receives fragmented ions from fragmentation region  118 . In some embodiments, configuration  112  further includes an optional second ion shutter  134  that at least partially defines second drift field region  132  and fragmentation region  118  when energized and facilitates flow communication between regions  118  and  132  when de-energized. In other embodiments, rather than second ion shutter  134 , configuration  112  further includes an optional ion trap  135  similar in design, construction, and operation as ion trap reactor  108 . Such ion trap  135  positioned between fragmentation region  118  and second drift field region  132  is configured to provide similar operational results as second ion shutter  134 , i.e., release fragmented ions into second drift tube  130  as an alternative to using a shutter grid. 
     ITMS detection system  100  also includes an ion collector  136  that includes a collector shield grid, i.e., an aperture grid  138  and a collector electrode  140 , e.g., a Faraday plate positioned just downstream of aperture grid  138 . Collector electrode  140  is coupled to a spectral analysis device  142  that includes at least one current-to-voltage amplifier (not shown). ITMS detection system  100  further includes an ITMS control system  144  that includes a processing device  146 . ITMS control system  144  is operatively coupled to ion trap reactor  108 , retaining grid  110 , sequential annular electrodes E 1 -E 7 , electric field generation devices  120 , first ion shutter  128 , second ion shutter  134  (if installed), second ion trap  135  (if installed), E 8 -E 14 , aperture grid  138 , collector electrode  140 , and spectral analysis device  142 . Casing  102  also defines a collector region  148  coupled in flow communication with second drift field region  132  and gas outlet tube  106 . 
     As used herein, the terms “processor” and “processing device” are not limited to just those integrated circuits referred to in the art as a computer, but broadly refers to a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits, and these terms are used interchangeably herein. In the embodiments described herein, memory may include, but is not limited to, a computer-readable medium, such as a random access memory (RAM), and a computer-readable non-volatile medium, such as flash memory. Alternatively, a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), and/or a digital versatile disc (DVD) may also be used. Also, in the embodiments described herein, additional input channels may be, but are not limited to, computer peripherals associated with an operator interface such as a mouse and a keyboard. Alternatively, other computer peripherals may also be used that may include, for example, but not be limited to, a scanner. Furthermore, in the exemplary embodiment, additional output channels may include, but not be limited to, an operator interface monitor. 
     Also, as used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by personal computers, workstations, clients and servers. 
     Further, as used herein, the term “non-transitory computer-readable media” is intended to be representative of any tangible computer-based device implemented in any method or technology for short-term and long-term storage of information, such as, computer-readable instructions, data structures, program modules and sub-modules, or other data in any device. Therefore, the methods described herein may be encoded as executable instructions embodied in a tangible, non-transitory, computer readable medium, including, without limitation, a storage device and/or a memory device. Such instructions, when executed by a processor, cause the processor to perform at least a portion of the methods described herein. Moreover, as used herein, the term “non-transitory computer-readable media” includes all tangible, computer-readable media, including, without limitation, non-transitory computer storage devices, including, without limitation, volatile and nonvolatile media, and removable and non-removable media such as a firmware, physical and virtual storage, CD-ROMs, DVDs, and any other digital source such as a network or the Internet, as well as yet to be developed digital means, with the sole exception being a transitory, propagating signal. 
     Furthermore, as used herein, the term “real-time” refers to at least one of the time of occurrence of the associated events, the time of measurement and collection of predetermined data, the time to process the data, and the time of a system response to the events and the environment. In the embodiments described herein, these activities and events occur substantially instantaneously. 
     Processing device  146  and other processors (not shown) as described herein process information transmitted from a plurality of electrical and electronic devices that include, without limitation, spectral analysis device  142  and feedback devices (not shown) within ITMS detection system  100 . Memory devices (not shown) and storage devices (discussed further below) store and transfer information and instructions to be executed by processing device  146 . Such memory devices and storage devices can also be used to store and provide temporary variables, static (i.e., non-volatile and non-changing) information and instructions, or other intermediate information to processing device  146  during execution of instructions by processing device  146 . Instructions that are executed include, but are not limited to, analysis of signals transmitted from spectral analysis device  142 . The execution of sequences of instructions is not limited to any specific combination of hardware circuitry and software instructions. ITMS detection system  100  also includes a data storage device  150  coupled to processing device  146 . Data storage device  140  stores the data generated by processing device  146 , such data also retrievable through processing device  146 . 
     In operation, a collection device (not shown) is coupled to gas inlet tube  104  and collects gaseous samples  152  from an object of interest (not shown). In some embodiments, rather than gaseous samples, inlet tube  104  channels particulate samples that are then vaporized to generate gaseous samples  152 . Gaseous samples  152  are channeled to the diffuser region portion of ion trap reactor  108  for expanding gaseous samples  152  prior to entry into the ionization chamber portion of ion trap reactor  108 .  63 Ni emits low-energy β-particles into ion trap reactor  108  and the β-particles ionize samples  152  while in the gaseous phase, thereby forming positive ions, negative ions, and free electrons. Ion trap reactor  108  is substantially a field-free region. Therefore, increasing a population density of the ions and electrons within ion trap reactor  108  is facilitated as a function of the flux of β-particles. As the ions are being generated in ion trap reactor  108  to increase the stored ion population  154  therein, retaining grid  110  is maintained at a slightly greater potential than the potential of ion trap reactor  108  to induce a retention field and reduce the potential for ion leakage from ion trap reactor  108 . An electric field is then induced across ion trap reactor  108  and, depending on the polarity of the induced electric field, the positive ions or the negative ions are pulsed from ion trap reactor  108 , through a high-voltage “kickout pulse”, and injected into first drift field region  116  through retaining grid  110 . The ions of the opposite polarity are attracted to the walls of ion trap reactor  108  and are discharged there. The pulses are controlled through ITMS control system  144 . 
     First drift field region  116  extends from retaining grid  110  to first ion shutter  128 . For those systems that use negative ions, annular electrodes E 1  through E 7  are energized to voltages that are sequentially less negative between retaining grid  110  to first ion shutter  128 , thereby inducing a constant positive field. Motion is induced in the negative ions from the initial pulse in ion trap reactor  108  and the ions are channeled through first drift field region  116  to first ion shutter  128 . First ion shutter  128  induces a voltage that is less negative than the voltage of electrode E 1  and is more negative than the voltage of electrode E 7 . ITMS control system  144  regulates the velocities of the ions injected from ion trap reactor  108  as they drift through first drift field region  116  toward first ion shutter  128  such that a selected portion  156  of ions injected into region  116  arrive at shutter  128  at a predetermined time, while a substantial amount of a non-selected portion  158  of ions arrive later due to the slower velocities or faster (not shown) due to the higher velocities. As such, ITMS control system  144  regulates the voltage of first ion shutter  128  for a first predetermined temporal period, thereby injecting a substantial amount  160  of the selected portion  156  of ions from first drift field region  116  into fragmentation region  118 . A significant amount of the non-selected portion  158  of ions are not permitted to transit through first ion shutter  128  when the voltage is again adjusted by ITMS control system  144  to block such ions and molecules that are subsequently discarded, thereby reducing injection of the non-selected portion of ions and into fragmentation region  118 . 
     Also, in operation, ITMS control system  144  regulates electric field generation device  120  to modify the selected portion of ions, thereby generating predetermined ion fragments  162  within fragmentation region  118  through regulating a voltage and frequency of the controllable electric field generated between electrodes  124  and  126 . The electric field dissociates a first portion of the selected portion  160  of ions injected into fragmentation region  118  into a first portion  164  of the predetermined ion fragments for further transmission to second field drift region  132 . Fragmentation of selected ions  162  generates ion fragments  164  that have a different mobility from unmodified ions  166  that generate different peaks on the associated output spectrum. As such, fragmentation facilitates distinguishing between two different, but intermingled ion populations that would otherwise have similar mobilities, since the modified versions of these fragment ions  164  will have dissimilar mobilities from those of unmodified ions  166 . 
     Further, in operation, at least some of those ions  168  of the non-selected portion of ions  158  that made it into fragmentation region  118  are also modified to further distinguish the resultant dissociated non-selected ions  170  from the predetermined ion fragments  162  under consideration due to the different mobilities. The dissociated non-selected ions  170  are discarded. In alternative embodiments, none of the non-selected ions  158  are dissociated into fragments, but are discarded regardless. 
     Moreover, for those embodiments that include optional second ion shutter  134 , in operation, the selected ion fragments under consideration  164  arrive at second ion shutter  134  at different times than most of the other ions, molecules, and fragments due to the different mobilities. As such, ITMS control system  144  regulates the voltage of second ion shutter  134  for a second predetermined temporal period, thereby injecting a substantial amount  172  of the selected portion  164  of the predetermined fragmented ions from fragmentation region  118  into second drift field region  132 . A significant amount of the non-selected portion of ions  170  and fragments  166  are not permitted to transit through second ion shutter  134  when the voltage is again adjusted by ITMS control system  144  to block such ions  170  and fragments  166  that are subsequently discarded, thereby reducing injection of the non-selected portion of ions  158  into second drift field region  132 . 
     Second drift field region  132  extends from a region between the downstream side of electrodes  124  and  126 , or second ion shutter  134  (if installed), to collector region  148  defined by ion collector  136  and casing  102 . Collector electrode  140  is positioned on the opposite side of drift field region  112  from electrodes  124  and  126 , or second ion shutter  134  (if installed), and is held at, or near, a ground potential. For those systems that use negative ions, annular electrodes E 8  through E 14  are energized to voltages that are sequentially less negative than between electrodes  124  and  126 , or second ion shutter  134  (if installed), to collector electrode  140 , thereby inducing a constant positive field. For those embodiments that include optional ion trap  135  rather than optional second ion shutter  134 , such ion trap  135  positioned between fragmentation region  118  and second drift field region  132  is configured to provide similar operational results as second ion shutter  134 , i.e., release fragmented ions into second drift tube  130  as an alternative to using a shutter grid. 
     For such embodiments with second ion shutter  134 , ITMS control system  144  regulates the voltage of second ion shutter  134  for a second predetermined temporal period, thereby injecting a substantial amount  172  of the selected portion  164  of fragmented ions from fragmentation region  118  into second drift field region  132 . For those embodiments that include optional ion trap  135  rather than optional second ion shutter  134 , such ion trap  135  positioned between fragmentation region  118  and second drift field region  132  is configured to provide similar operational results as second ion shutter  134 , i.e., release fragmented ions into second drift tube  130  as an alternative to using a shutter grid. Motion is induced in the negative ions through the graduated potential along second field drift region  132 . As such, ITMS control system  144  regulates the velocities of the selected portion  172  of the predetermined fragmented ions  164  injected from fragmentation region  118  as they drift through second drift field region  132  toward collector electrode  140 . The selected portion  172  of the predetermined fragmented ions  164  injected into region  132  arrive at collector electrode  140  at a predetermined time, while any remaining non-selected ions  170  and ion fragments  166  are expected to arrive at a different drift time due to the different velocities. A significant amount of the non-selected portion of ions  170  and ion fragments  166  are not permitted to transit through second ion shutter  134  (or ion trap  135 ) when the voltage is again adjusted by ITMS control system  144  to block non-selected ions  170  and ion fragments  166  that are subsequently discarded, thereby reducing injection of the non-selected  170  portion of ions and ion fragments  166  into second field drift region  132 . 
     Therefore, in operation, with, or without second ion shutter  134  (and, similarly, with or without ion trap  135 ), the selected portion  172  of the predetermined fragmented ions  164  drift through second field drift region  132  to collector electrode  140  through aperture grid  138 . Aperture grid  138  induces a voltage that is less negative that the voltage of electrode E 8  and is more negative than the voltage of collector electrode  140  that is maintained at substantially ground potential. Signals representative of the ion population at collector electrode  140  are generated and transmitted to spectral analysis device  142  to determine the constituents in collected gas samples  152 , and a detection spectrum representative of the ion or fragment ions detected at collector electrode  140  through spectral analysis device  142  coupled to collector electrode  140 . 
     The exemplary embodiment as described above is directed to an ITMS detection system  100  configured to use negative ions. However, in some embodiments, ITMS detection system  100  is configured to use positive ions. In such embodiments, the electric field induced across ion trap reactor  108  has a polarity to “kick out” the positive ions rather than the negative ions such that the positive ions are pulsed from ion trap reactor  108  through the high-voltage “kickout pulse”, and injected into first drift field region  116  through retaining grid  110 . The ions of the opposite polarity are attracted to the walls of ion trap reactor  108  and are discharged there. Motion is induced in the positive ions from the initial pulse in ion trap reactor  108 . Also, in such circumstances, annular electrodes E 1  through E 7  are energized to voltages that are sequentially less positive between retaining grid  110  to first ion shutter  128  to facilitate inducing motion in the positive ions such that the ions are channeled through first drift field region  116  to first ion shutter  128 . First ion shutter  128  induces a voltage that is less positive than the voltage of electrode E 1  and is more positive than the voltage of electrode E 7 . The remainder of ITMS detection system  100  is further configured for positive ions rather than negative ions and operation thereof is executed accordingly. 
       FIG. 2  is a schematic view of an alternative ion trap mobility spectrometer (ITMS) detection system  200  (not drawn to scale). System  200  is similar to system  100  (shown in  FIG. 1 ) with the difference that system  200  includes a dopant injection system  202  coupled in flow communication with fragmentation region  118 . Some dopants further enhance the specificity of identification of substances, for example, and without limitation, some typical dopants used in trace detection of explosives are chlorinated compounds, e.g., in a negative ion mode, and without limitation, dichloromethane, hexachloroethane, and chloroform, and, in positive ion modes, and without limitation, acetone and ammonia-based compounds, e.g., ammonium carbamate, and anhydrous ammonia. Therefore, in operation of system  200 , a dopant  204  is injected into fragmentation region  118  and at least a portion of injected dopant  204  is mixed with the selected portion of ions  160  from first drift field region  116 . Operation of system  200  is similar to that of system  100  as described above, with the primary difference of the dopant altering the population of predetermined fragmented ions  164  and  172  with constituents including, without limitation, adducts (not shown). 
     TOF ion mobility spectrometer (IMS) detection systems (not shown) are similar to ITMS detection systems  100  and  200  with one difference of the IMS detections systems is that they do not include ion trap features through a retaining grid that is maintained at a relatively constant voltage to trap the ions in the ionization chamber. Rather, IMS detection systems include an ion gate device (sometimes referred to as an ion shutter), e.g., a Bradbury-Nielsen gate. Similar to retaining grid  110  of systems  100  and  200 , as the ions are being generated in the IMS ionization region to increase the ion current therein, the ion gate device is maintained at a relative voltage great enough to substantially prevent ion current transmitting into the adjacent drift region. The relative voltage difference between the ion gate device is then temporarily removed and the stored ions are pulsed from the ionization region into the drift region through the ion gate device. The temporal period of gate de-energization is predetermined. The voltage applied of the ion gate device is then re-established, thereby substantially halting ion entry from the ionization region into the drift region. Therefore, rather than pulsing the ions through a consistently energized retaining grid as is done for ITMS systems  100  and  200 , in the IMS systems the ion gate is temporarily de-energized. 
       FIG. 3  is a graphical view, i.e., graph  300  of exemplary spectra that may be produced using ITMS detection systems  100  and  200  (shown in  FIGS. 1 and 2 , respectively). Graph  300  includes a y-axis  302  representative of ion intensity, i.e., detector response in arbitrary units (au). Also, graph  300  includes an x-axis  304  representative of drift time in arbitrary units (au). In the exemplary embodiment, a sample of ethylene glycol dinitrate (EGDN) [C 2 H 4 (ONO 2 ) 2 ], a common constituent of explosive devices, is introduced into IMS detection system  200 , system  200  including tandem reactive drift tube configuration  112  (shown in  FIGS. 1 and 2 ). 
     Graph  300  includes a first trace  306  representing a spectral analysis of the EGDN sample with the fragmentation system off, i.e., electric field generation device  120  in fragmentation region  118  (both shown in  FIGS. 1 and 2 ) removed from service. First trace  306  includes a chloride ion (Cl − ) peak  308  and a M.Cl −  adduct peak  310 . While peak  308  is a dopant peak, peak  310  may indicate the presence of EGDN (EGDN*Cl − ). A peak  312  may indicate the presence of trace amounts of NO 3   − . 
     Graph  300  also includes a second trace  314  representing a spectral analysis of the EGDN sample with the fragmentation system on, i.e., electric field generation device  120  in fragmentation region  118  placed in service. Second trace  314  includes a nitrate (NO 3   − ) peak  316  as a result of the decomposition of EGDN, such peak indicative of the presence of EGDN. Notably, M.Cl −  adduct peak  310  is not found with second trace  314  since the M.Cl −  ions were decomposed using the fragmentation system. The peak just to the left of nitrate peak  316  is at least partially due to some additional Cl −  from peak  308 . Therefore, use of the fragmentation system during sample analysis in conjunction with the remainder of the tandem reactive dual drift tube and dual shutter configuration  112  significantly improves the sample analyses for substances of interest, such as EGDN. 
       FIG. 4  is another graphical view, i.e., graph  400  of exemplary spectra that may be produced using ITMS detection systems  100  and  200  (shown in  FIGS. 1 and 2 , respectively). Graph  400  includes a y-axis  402  representative of ion intensity, i.e., detector response in arbitrary units (au). Also, graph  400  includes an x-axis  404  representative of drift time in arbitrary units (au). In the exemplary embodiment, a sample of ethylene glycol dinitrate (EGDN) [C 2 H 4 (ONO 2 ) 2 ], a common constituent of explosive devices, is introduced into IMS detection system  200 , system  200  including tandem reactive drift tube configuration  112  (shown in  FIGS. 1 and 2 ). Only the analyte ions of EGDN (shown as  310  in  FIG. 3 ), however, are transferred through the first shutter  128  into the second drift tube  130  defining the second drift region  132  whereas all other ions of different mobilities are excluded from passing the shutter. 
     Graph  400  includes a first trace  406  representing a spectral analysis of the analyte ions of the EGDN sample with the fragmentation system off, i.e., electric field generation device  120  in fragmentation region  118  (both shown in  FIGS. 1 and 2 ) removed from service. First trace  406  includes an M.Cl −  adduct peak  410 , peak  410  may indicate the presence of EGDN (EGDN*Cl − ). No other peaks such as the dopant peak previously shown as  308  in  FIG. 3  are detected in the spectrum  406  displayed in  FIG. 4 . 
     Graph  400  also includes a second trace  412  representing a spectral analysis of the analyte ions (M.Cl) −  of the EGDN sample with the fragmentation system on, i.e., electric field generation device  120  in fragmentation region  118  placed in service. Second trace  412  includes a nitrate (NO 3   − ) peak  414  as a result of the decomposition of the analyte ions of EGDN, such peak indicative of the presence of EGDN. Notably, this peak was not present when the fragmentation system was off. Moreover, the intensity of a M.Cl −  adduct peak  416  is much lower with second trace  412  compared to the intensity of  410  since the M.Cl −  ions were decomposed using the fragmentation system. Therefore, use of the fragmentation system during sample analysis in conjunction with the remainder of the tandem reactive dual drift tube and dual shutter configuration  112  significantly improves the sample analyses for substances of interest, such as EGDN. 
     ITMS detection systems  100  and  200  (shown in  FIGS. 1 and 2 , respectively) facilitate ion fragmentation that further facilitates identifying chemical families primarily based on the way the analyte ions fragment. In general, ions in a gas phase at ambient pressure are not as robust as molecules in air at ambient pressure, i.e., the electrostatic charge on the ions increase the vulnerability of the bonds in the ion to weakening. Also, in general, increasing the thermal energy of the ions increases the vibratory motion, thereby further weakening the covalent bonds of the ions and, in cooperation with destabilizing effects of the ionic charge, rendering the bonds unstable until covalent bond cleavage, i.e., ion fragmentation is achieved. One method of increasing the temperature of the gaseous ions is through adding thermal energy to the gas by increasing the gas temperature through a heating device (not shown) to preheat the gas prior to injection into systems  100  and  200 . Another method includes using the electric fields induced as described above to rapidly increase the kinetic energy of the ions that translates into increasing the thermal energy, and as such, the vibration of the ions. Use of the electric fields already present facilitates weakening of the ion bonds at much lower temperatures. Increasing the strength of the electric fields accelerates ion fragmentation. Because substances of a given family have similar molecular structures and similar bonding and ionic characteristics within the core structure of the molecule, such ions therefore tend to break into pieces corresponding to the characteristics of such substance(s). As such, further fragmentation of the ions into selected and known ion fragments further facilitates identifying chemical families. 
     The portable, atmospheric pressure, tandem reactive IMS devices described herein provide cost-effective systems and methods for improving detection of materials of interest from an object or person. The systems and methods described herein use a detector having two sequentially arranged drift tubes which are separated by shutters facilitating ions of a user-selected, i.e., library-defined drift time to be introduced into the second drift tube whereas other ions of a different mobility are discarded as needed. The IMS and ITMS devices disclosed herein facilitate multiple opportunities to isolate ions of interest including ion separation and selection in the first drift tube, predetermined modification through fragmentation through a controllable electric field, and selected transmission into the second drift tube ultimately ending with specific identification of the ions. Regulation of the electric field strength and temperature analyte ions from one compound may dissociate and form dissociation products that can further be characterized, while ions from another compound may dissociate as well but form different products or may even not dissociate at all. As such, this dissociation information is important for providing another dimension of characterizing the mobility of ions by their stability and their dissociation products which provides additional confidence in the presence or absence of peaks that facilitates determining if an alarm could be generated or rejected. The results are more easily interpreted and provide more definitive information that can be used for the characterization of ions since only ions of a particular drift time are exposed to the high electric field and the associated fragmentation. Consequently substantially all dissociation products detected in the second drift tube originate from the ions selected from the first drift tube and subsequently fragmented. Moreover, the additional optional introduction of dopants facilitates further modification of the selected ions through chemical reactions with or without dissociation. As such, the systems described herein facilitate an additional level of selectivity that dramatically reduces the false alarm rate from that observed on traditional IMS and ITMS systems. Therefore, the portable mobility spectrometers described herein facilitate substance analysis with higher confidence while maintaining atmospheric pressure operation. 
     A technical effect of the systems and methods described herein includes at least one of: (a) substantially decreasing the frequency of false alarms in TOF-IMS and -ITMS detection systems; (b) facilitating ions of a user-selected, i.e., library-defined drift time to be introduced into a second drift tube where other ions of a different mobility are discarded as needed; (c) executing predetermined modification of selected ions through fragmentation with a controllable electric field; (d) regulating the electric field strength and temperature such that analyte ions from one compound dissociate and form dissociation products that can further be characterized while ions from other compounds either dissociate and form different products or not dissociate at all; (e) increasing dissociation information for further characterizing the mobility of ions by their stability and their dissociation products; (f) increasing confidence in the presence or absence of peaks that facilitates determining if an alarm could be generated or rejected; and (g) weakening ionic bonds through leveraging weakening of such bonds due to the electrostatic charge of the ion and increased thermal energy of the ion until ion fragmentation into the predetermined ion fragments is achieved, thereby further facilitating identifying chemical families primarily based on the way the analyte ions fragment. 
     Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
     Some embodiments involve the use of one or more electronic or computing devices. Such devices typically include a processor, processing device, or controller, such as a general purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a reduced instruction set computer (RISC) processor, an application specific integrated circuit (ASIC), a programmable logic circuit (PLC), a field programmable gate array (FPGA), a digital signal processing (DSP) device, and/or any other circuit or processing device capable of executing the functions described herein. The methods described herein may be encoded as executable instructions embodied in a computer readable medium, including, without limitation, a storage device and/or a memory device. Such instructions, when executed by a processing device, cause the processing device to perform at least a portion of the methods described herein. The above examples are exemplary only, and thus are not intended to limit in any way the definition and/or meaning of the term processor and processing device. 
     This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.