Abstract:
Mass spectometer system and method of use are disclosed. Briefly described, one embodiment of the mass spectrometry system, among others, includes a radio frequency multipole assembly, an inner structure, and a laser diode array system. The inner structure has an outside, an inside, and an opening. The inner structure substantially surrounds the radio frequency multipole assembly. The laser diode array system is disposed on the outside of the inner structure adjacent the side opening such that laser radiation emitted from the laser diode array system travels through the side opening.

Description:
BACKGROUND 
     Mass spectrometry systems are analytical systems used for quantitative and qualitative determination of the compositions of materials, which include chemical mixtures and biological samples. In general, a mass spectrometry system uses an ion source to produce electrically charged particles (e.g., molecular or polyatomic ions) from of the material to be analyzed. Once produced, the electrically charged particles are introduced to the mass spectrometer and separated by mass analyzer based on their respective mass-to-charge ratios. The abundance of the separated electrically charged particles are then detected and a mass spectrum of the material is produced. The mass spectrum is analogous to a fingerprint of the sample material being analyzed. The mass spectrum provides information about the mass-to-charge ratio of a particular compound in a mixture sample and, in some cases molecular structure of that component in the mixture. 
     For determining molecular weight of a compound, mass spectrometry systems employing a single mass analyzer are widely used. These analyzers include a quadrupole (Q) mass analyzer, a time-of-flight mass analyzer (TOFMS), ion trap (IT-MS), and etc. For more complicated molecular structure analysis, however, tandem mass spectrometers (Tandem-MS or MS/MS) are often needed. Tandem mass analyzers typically consist of two mass analyzers of the same or of different types, for instance TOF-TOF MS or Q-TOF MS. In a tandem MS analysis, ionized particles are sent to the first mass analyzer and an ion of particular interest is selected. The selected ion is transmitted to a dissociation cell where the selected ion is fragmented. The fragment ions are transmitted to the second mass analyzer for mass analysis. The fragmentation pattern obtained from the second mass analyzer can be used to determine the structure of the corresponding molecules. 
     For example, in a triple quadrupole mass spectrometer an ionization source produces a plurality of parent ions. The first quadrupole mass analyzer is used to select a particular parent ion. Then, the selected parent ion is dissociated into daughter ions in the second quadrupole via photodissociation and/or collisionally induced dissociation. Subsequently, the third quadrupole mass analyzer is used to separate the daughter ions based on their respective mass-to-charge ratios. The resulting mass spectrum can be used to identify the daughter ions, which can be useful in identifying the structure of the selected parent ion. 
     In the example described above, the second quadrupole can be used as a collision cell to facilitate collision induced dissociation of the selected parention. When the parent ions collide with a background gas (normally an inert gas such as argon), a portion of the translation energy of the parent ions is converted into activation energy that is sufficiently high to break certain molecular bonds. The fragment pattern produced characterizes the original molecule and provides information about its structure. 
     In the example described above, a laser can be used to photodissociate the parent ions in the second quadrupole instead of collisions with gas molecules. Current photodissociation techniques use a cross-directed laser beam and a complex mirror system or an on-axis directed laser beam to create a high photon flux to dissociate the molecular ions. However, these photodissociation techniques require expensive high power lasers (e.g., CO 2  laser). Cross-directed laser beam techniques require precision mirror alignment, which can be expensive and time consuming to achieve. On-axis directed laser beam techniques are problematic because of significant ion loss. 
     Thus, there is a need in the industry for a mass spectrometry system that uses a photodissociation technique that overcomes at least these disadvantages. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide for mass spectrometry systems and methods of use. Briefly described, one embodiment of the mass spectrometry system, among others, includes a radio frequency multipole assembly, an inner structure, and a laser diode array system. The inner structure has an outer surface, an inner surface, and an opening. The inner structure substantially surrounds the radio frequency multipole assembly. The laser diode array system is disposed on the outer surface of the inner structure adjacent the opening such that laser radiation emitted from the laser diode array system travels through the opening. 
     Embodiments of the present invention also include methods for dissociating an ion. In this regard, one embodiment of such a method, among others, includes producing an ion and focusing the ion into a dissociation cell/laser diode array system. The dissociation cell/laser diode array system includes a radio frequency multipole assembly, a structure that substantially surrounds the radio frequency multipole assembly and a laser diode array system disposed on the outer surface of the structure. The method also includes producing laser radiation with a laser diode array system and photodissociating the ion. 
    
    
     Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Aspects of the invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
     FIG. 1 is a block diagram illustrating a representative embodiment of a mass spectrometer system having a dissociation cell/laser diode array system of the present invention. 
     FIG. 2 is a block diagram illustrating another representative embodiment of a mass spectrometer system having a dissociation cell/laser diode array system of the present invention. 
     FIG. 3 is a perspective view of a dissociation cell/laser diode array system of the present invention. 
     FIG. 4A is a cross-sectional view of an embodiment of a laser diode array system used in the dissociation cell/laser diode array system shown in FIG.  3 . 
     FIG. 4B is a cross-sectional view of another embodiment of another laser diode array system used in the dissociation cell/laser diode array system shown in FIG. 3, in which the laser diode array system includes a lens system. 
     FIG. 4C is a cross-sectional view of another embodiment of another laser diode array system used in the dissociation cell/laser diode array system shown in FIG. 3, in which the laser diode array system is aligned off-axis relative to the central longitudinal axis of the mass analyzer. 
     FIG. 5 is a side perspective view of another dissociation cell/laser diode array system of the present invention, in which the laser diode array system is located adjacent an outer structure. 
     FIG. 6A is a cross-sectional view of an embodiment of the dissociation cell/laser diode array system shown in FIG. 5, in which the laser diode array system includes a lens system. 
     FIG. 6B is a cross-sectional view of an embodiment of the dissociation cell/laser diode array system shown in FIG. 5, in which the laser diode array system is aligned off-axis relative to the central longitudinal axis of the mass analyzer. 
     FIG. 7A is a side perspective view of a dissociation cell/laser diode array system of the present invention, in which the power cable of the laser diodes is wound helically around the inner structure. 
     FIG. 7B is a side perspective view of another embodiment of a dissociation cell/laser diode array system of the present invention, in which the power cable of the laser diode array system is wound helically around the outer structure. 
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention provide for dissociation cell/laser diode array systems that can be used in a mass spectrometry system that can overcome some of the disadvantages discussed above. The dissociation cell/laser diode array system includes one or more laser diode array systems to produce laser radiation. The laser diode array system is less expensive than equivalent laser systems (e.g., CO 2  gas laser systems). The laser diode array system includes a laser diode array. The laser diode arrays are compact and provide a high density photon flux with power supply efficiencies approaching fifty percent. In this regard, the dissociation cell/laser diode array systems of the present invention are capable of providing a high density photon flux along an extended portion of the ion beam. 
     FIG. 1 is a block diagram that illustrates a mass spectrometry system  10  that includes an ion source  12 , a dissociation cell/laser diode array system  14 , and a mass analyzer/detector  16 . The dissociation cell/laser diode array system  14  can include a radio frequency (RF) multipole assembly (e.g., quadrupole mass assembly, hexapole mass assembly, and octopole mass assembly) and one or more laser diode array systems, which will be described in more detail below. 
     The ion source  12  is typically a device capable of forming ions from a sample to be analyzed. The ion source  12  can be any appropriate mass spectrometry ion source appropriate for the particular application such as, for example, an electrospray source, a photoionization source, a matrix assisted laser desorption ion source, an electron beam ionization source (i.e., continuous or pulsed), an atmospheric pressure chemical ionization source, and a plasma source. 
     The mass analyzer/detector  16  can include a mass analyzer and a detector. The mass analyzer can include, for example, a time-of-flight (TOF) mass analyzer, an ion trap, a quadrupole mass analyzer, a magnetic sector mass analyzer, and an ion cyclotron resonance (ICR) mass analyzer. 
     The detector is a device for recording ions that are subjected to acceleration and deflection forces in mass spectrometry system, as is known in the art. The detector can include, for example, an electron multiplier detector, a channel electron multiplier detector, a microchannel plate multiplier detector, and a gas electron multiplier detector. 
     It should be noted that the mass spectrometry system  10  shown in FIG. 1 does not illustrate ion optic systems, mass spectrometry pumping equipment (e.g., turbo molecular pumps or oil diffusion pumps), mass spectrometry electronic components (e.g., power supplies), and the like. However these are known in the art and are often tailored for specific mass spectrometry systems. 
     FIG. 2 is a block diagram that illustrates a mass spectrometry system  20  that includes a dissociation cell/laser diode array system  28 . The mass spectrometry system  20  includes an ion source  22 , a first ion optic system  24 , a mass analyzer  26 , a dissociation cell/laser diode array system  28 , a second ion optic system  30 , and a mass analyzer/detector  32 . The ion source  22 , the dissociation cell/laser diode array system  28 , and the mass analyzer/detector  32  are analogous to the ion source  12 , the dissociation cell/laser diode array system  14 , and the mass analyzer/detector  16  shown in FIG.  1 . The mass analyzer  26  is typically a quadrupole mass analyzer, however, other mass analyzers, such as those described above, may be used in particular mass spectrometry configurations. 
     The ion optic systems  24  and  30  can be used for transmitting ions and manipulating a beam of ions. In particular, the ion optic systems  24  and  30  can, for example, focus or defocus a beam of ions. In addition, the ion optic systems  24  and  30  can alter ion energy and the ion beam energy distribution. 
     Generally, the ion optic systems  24  and  30  can be divided into two categories. In category one, the ion optic systems  24  and  30  use magnetic fields or electrostatic fields in various configurations such as, for example, an electrostatic einzel lens system and an electrostatic or a magnetic sector field system, and a multipole lens system. In category two, the ion optic systems  24  and  30  use a radio frequency electrical field such as that employed in RF multipole ion guides and RF ion funnels, which use of a series of ring electrodes. 
     FIG. 3 is a perspective view of a dissociation cell/laser diode array system  40 . The dissociation cell/laser diode array system  40  can be used in a mass spectrometry system to photodissociate an ion (AB + )  42  into an ion (A + )  44   a  and a neutral molecule (B)  44   b.    
     One embodiment of the dissociation celulaser diode array system  40  includes a quadrupole structure  46 , an inner structure  48 , and three laser diode array systems  52 . The inner structure  48  substantially surrounds the quadrupole structure  46 , while the three laser diode array systems  52  are disposed upon the outer surface  48   b  of the inner structure  48 . 
     The quadrupole structure  46  is a conventional electric RF multipole ion guide that is constructed of four circular electrically conductive rods of substantially the same geometric dimension. The rods are parallel to a central longitudinal axis  56 , and each rod is located a fixed distance from the central longitudinal axis  56  (as shown in FIGS.  4 A through  4 C). When radio frequency voltages of opposite polarities are alternately applied to the adjacent rods, a symmetric RF field is established inside the area defined by the rods. At any cross section of the symmetric RF quadrupole field, the potential distribution is a function of time and is characterized by the RF frequency. Other embodiments can include a RF multipole ion guide having a larger even number of rods (e.g., six rods or eight rods). RF multipole ion guides and the corresponding electronic components are known in the art. 
     The inner structure  48  substantially surrounds the quadrupole structure  46 , as shown in FIG.  3 . The inner structure  48  extends the length of the quadrupole structure  46 . However, the length of the inner structure  48  may be longer or shorter than the quadrupole structure  46 , as can be determined by one skilled in the art for a particular application. FIG. 3 illustrates the inner structure  48  as a cylinder; however, the inner structure  48  can have an elliptical or a polygonal shape to effect focusing of the laser radiation to an intense region coaxial with the inner structure  48  axis and thus form an optical cavity. 
     In the preferred embodiment, the inner surface  48   a  of the inner structure  48 , the surface facing the quadrupole structure  46 , is a highly internally optic-reflective surface that can reflect the laser radiation. Typically, the inner structure  48  is made of a material (e.g., stainless steel, aluminum or fused quartz) that is not highly internally optic-reflective. Therefore, the inner surface  48   a  of the inner structure  48  can be polished or coated with a highly internally optic-reflective material such as, for example, a reflective metal (e.g., gold or aluminum), a reflective stack of dielectric layers of material (e.g., zinc sulfide (ZnS), and cryolite). Alternatively, an absorptive coating (e.g., “black gold”) can be applied if reflection is not desired (i.e., an optic absorptive surface). 
     In a preferred embodiment, the inner structure  48  has a diameter of about 5 to 25 millimeters and a length of about 50 to 150 millimeters. The inner structure  48  has a wall thickness of about 0.25 to 1.0 millimeters. The inner structure  48  includes the opening  50  along the longitudinal axis of the quadrupole structure  46 . The opening  50  extends the length of the inner structure  48 . However, the opening  50  may extend a shorter distance than the length of the inner structure  48 . 
     In another embodiment of the inner structure  48 , the opening  50  can be represented as a slot or multiple slots through which laser radiation can pass. One or more laser diode array systems, described below, can be associated with the slot or slots. Preferably, a single laser diode array system is associated with a single slot, so that the number of slots equals the number of laser diode array systems. The slots can be located on any portion of the inner structure  48 . 
     In another embodiment, the opening  50  can be covered by a transparent material. The transparent material can be made of any material that laser radiation can pass through such as, for example, glass, fused quartz, and or a polymer. In addition, the transparent material can act as a lens system that focuses or defocuses the laser radiation. 
     FIGS. 4A through 4C are cross-sectional views illustrating three different laser diode array system configurations that can be used in the dissociation cell/laser diode array system  40  shown in FIG.  3 . FIG. 4A is a cross-sectional view of a laser diode array system  52   a  used in the dissociation cell/laser diode array system  40   a , wherein the cross-section is taken along the laser diode array system  52   a  perpendicular to the central longitudinal axis  56 . 
     The laser diode array system  52   a  shown in FIG. 4A includes a laser diode array  53   a . The laser diode array  53   a  is composed of many individual semiconductor lasers stacked side-by-side on a common substrate. The laser diode array  53   a  emits a “ribbon” shaped beam of laser radiation that passes through the opening  50  of the inner structure  48  and can be absorbed by an ion causing the ion to photodissociate. Alternatively, the laser radiation can be internally reflected on the inside surface  48   a  of the inner structure  48 . 
     In this embodiment, the laser radiation is emitted at about a 40° angle, as shown by arrow A, by the laser diode array  53   a . In addition, the opening  50  is aligned on-axis with the central longitudinal axis  56  of the quadrupole structure  46 . In general, the ion beam (not shown) is concentrated along the central longitudinal axis  56  of the quadrupole structure  46 , so that on-axis alignment may increase the probability of photodissociation of the ions. 
     The wavelength of the laser radiation emitted from the laser diode array  53   a  can be any wavelength that causes the desired photodissociation. For example, the laser diode array  53   a  (available from Cutting Edge Optronics Incorporated) can emit laser radiation having wavelengths of 795 nanometers, 808 nanometers, 1450 nanometers, 1540 nanometers, and the like. Selection of a laser diode array having a particular wavelength depends upon the type of bond that needs to be broken, which can be determined by one skilled in the art. 
     FIG. 4B is a cross-sectional view of another laser diode array system  52   b  used in the dissociation cell/laser diode array system  40   b , wherein the cross-section is taken along the laser diode array system  52   b  perpendicular to the central longitudinal axis  56 . In this embodiment, the laser diode array system  52   b  includes the laser diode array  53   a  and a lens system  54   b . The lens system  54   b  focuses the laser radiation emitted from the laser diode array  53   b  so that the laser radiation has about a 1° angle, as shown by arrow B. Since the ion beam is concentrated along the central longitudinal axis  56  of the quadrupole structure  46 , focusing the laser radiation onto the longitudinal central axis  56  enhances the probability of photodissociation of the ions. 
     FIG. 4C is a cross-sectional view of another laser diode array system  52   c  used in the dissociation cell/laser diode array system  40   c , wherein the cross-section is taken along the laser diode array system  52   c  perpendicular to the central longitudinal axis  56 . 
     The laser diode array system  52   c  is aligned off-axis relative to the central longitudinal axis  56  of quadrupole structure  46 . By aligning the laser diode array system  52   c  offaxis, the laser radiation is less likely to be reflected back to the opening  50 . It should be noted that the internal reflection of the laser radiation within the inner structure  48  might be altered by using inner structures having different geometric shapes, as discussed above. Alternatively, an absorptive coating (e.g., “black gold”) can be applied if reflection is not desired (i.e., an optic absorptive surface). 
     FIG. 3 illustrates three laser diode array systems for demonstrative purposes and one or more laser diode array systems  52  can be used in a dissociation cell/laser diode array system in accordance with this embodiment of the invention. In addition, multiple rows of laser diode array systems can be included in a dissociation cell/laser diode array system. Furthermore, a dissociation cell/laser diode array system can include laser diode array systems that can emit laser radiation having different wavelengths (i.e., laser diode arrays emitting laser radiation at 795 nanometers and 1540 nanometers). 
     The laser diode array system  52  can be operated in a continuous mode or in a pulsed mode. In the preferred embodiment, the laser diode array system  52  is operated in a pulsed mode to lessen the heat generated by the laser diode array system  52  and match the duty cycle of the associated mass spectrometer. 
     In general, the laser diode array system  52  can include a laser diode array and a lens system. In addition, the laser diode array system  52  can include one or more lenses. 
     The dissociation cell/laser diode array system  40  can be used in conjunction with a dissociation gas (i.e., collision-induced dissociation). In this embodiment, the ions can be photodissociated or collisionally dissociated or a combination thereof 
     In addition, inert gas can be used to collisionally cool the ions, so that the ion beam narrows. Collisional cooling of the ion beam toward the central longitudinal axis  56  of the quadrupole structure  46  can be useful since the laser radiation can be focused toward the central longitudinal axis  56 , as is discussed in regard to FIGS. 4B and 4C. 
     FIG. 5 is a perspective view of a mass spectrometer/laser diode array system  60 . The dissociation cell/laser diode array system  60  can be used in a mass spectrometry system to photodissociate an ion (AB + )  62  into an ion (A + )  64 A and a neutral molecule (B)  64 B. 
     One embodiment of dissociation cell/laser diode array system  60  includes a quadrupole structure  66 , an inner structure  68 , an outer structure  70 , and three laser diode array systems  74 . The inner structure  68  substantially surrounds the quadrupole structure  66 , while the outer structure  70  substantially surrounds the inner structure  68  and may serve, with suitable end caps, to contain a dissociation gas. The laser diode array systems  74  are disposed adjacent the outer surface  70   a  of outer structure  70  and would serve as gas seals for openings (not shown) corresponding to the laser diode array systems  74 . 
     The quadrupole structure  66  is a conventional electric RF multipole ion guide comparable to the quadrupole structure  46  discussed in reference to FIG.  3 . In addition, the inner structure  68  and the laser diode array systems  74  are comparable to the inner structure  48  and the laser diode array systems  52 , discussed in reference to FIG.  3 . 
     The outer structure  70  substantially surrounds the inner structure  68  and the quadrupole structure  66 , as shown in FIG.  5 . The outer structure  70  extends the length of the inner structure  68  and the quadrupole structure  66 . However, the length of the outer structure  70  may be longer or shorter than the inner structure  68  and/or the quadrupole structure  66 , as can be determined by one skilled in the art for a particular application. FIG. 5 illustrates the outer structure  70  as a cylinder; however, the outer structure  70  can have an elliptical or polygonal shape. 
     Typically, the outer structure  70  can be made of a material such as, for example, stainless steel, or aluminum. In addition, the outer structure  70  can be made of a non-metallic material such as, for example, ceramic or polymer. 
     In this embodiment, the outer structure  70  has a diameter of about 30 to 75 millimeters, a length of about 50 to 300 millimeters, and a wall thickness of about 1 to 2 millimeters. 
     The outer structure  70  includes three outer structure openings that correspond to the three laser diode array systems  74 . The outer structure openings are aligned with the opening  72  of the inner structure  68  so that laser radiation can pass through the outer structure openings and opening  72 , as shown in FIGS. 6A and 6B. 
     The outer structure openings can be any length or width such that the laser radiation can be emitted through the outer structure openings. In addition, outer structure openings can be located on any position of the outer structure  68  so long as the laser radiation can be directed through an opening in the inner structure  68 . 
     In the embodiment shown in FIG. 5, the opening  72  does not have the same dimensions as the outer structure openings, however, the dimensions of the outer structure openings and the opening  72  should be chosen so that the laser radiation can pass through both the outer structure openings and the opening  72 . Thus, various configurations (e.g., dimensions, position, and shapes) of the outer structure openings and the opening  72  can be used with the dissociation cell/laser diode array system  60 . 
     In another embodiment, the outer structure openings are covered with a transparent material. The transparent material can be made of any material that laser radiation can pass through such as, for example, glass, fused quartz or a polymer. In addition, the transparent material can act as a lens system that focuses or defocuses the laser radiation. 
     The dissociation cell/laser diode array system  60  can be used in conjunction with a dissociation gas (i.e., collision-induced dissociation) or an ion cooling gas as described above and in the dissociation celulaser diode array system  40  discussed in reference to FIG.  3 . 
     FIGS. 6A and 6B are cross-sectional views illustrating two different laser diode array system configurations used in the dissociation celulaser diode array system  60  shown in FIG.  5 . FIG. 6A is a cross-sectional view of a laser diode array system  74   a  used in the dissociation celulaser diode array system  60   a , wherein the cross-section is taken along the laser diode array system  74   a  perpendicular to the central longitudinal axis  79 . 
     In this embodiment, the laser diode array system  74   a  includes the laser diode array.  76   a  and the lens system  78   a . The lens system  78   a  focuses the laser radiation emitted from laser diode array  76   a  so that the laser radiation has about a  11  angle, as shown by arrow B. The laser radiation is focused through the outer structure opening  76   a  and the inner structure opening  72  toward the central longitudinal axis  79  of the quadrupole structure  66 . Since the ion beam is concentrated along the central longitudinal axis  79 , focusing the laser radiation onto the central longitudinal axis  79  enhances the probability of photodissociation of the ions. 
     The laser diode array system  74   a  can include one or more lenses  78   a  to focus the laser radiation. As shown in FIG. 6A, the lenses can be located adjacent laser diode array  76   a  disposed on the outer structure  68 . In addition, the lenses can be separated from the laser diode array  76   a . For example, a first lens system can be located adjacent outer structure  70 , while a second lens system is located adjacent the inner structure  68 . 
     FIG. 6B is a cross-sectional view of a laser diode array system  74   b  used in the dissociation cell/laser diode array system  60   b  along the laser diode array system  74   b.    
     The laser diode array system  74   b  is aligned off-axis relative to the central longitudinal axis  79  of the quadrupole structure  66 . The laser radiation is focused through the outer structure opening  76   b  and the inner structure opening  72  toward the central longitudinal axis  79  of the quadrupole structure  66 . By aligning the laser diode array system  74   b  off-axis, the laser radiation is less likely to be reflected back to the opening  72 . It should be noted that the internal reflection of the laser radiation within the inner structure  68  might be altered by using an inner structure having different geometric shapes, as discussed above. Alternatively, an absorptive coating (e.g., “black gold”) can be applied if reflection is not desired (i.e., an optic absorptive surface). 
     FIG. 7A is a perspective view of a dissociation cell/laser diode array system  80  in which a power conductor (i.e., cord)  92  of the laser diode array systems  84  is wound helically around the inner structure  88 . Winding the power conductor  92  helically around the inner structure  88  produces an axial magnetic field when current passes through the power conductor  92 . The magnetic field produces a “magnetic bottle” effect that constrains the ions along the central longitudinal axis (not shown) of the quadrupole structure  86 . This can be advantageous because the laser radiation is focused along the central longitudinal axis of the quadrupole structure  86 , thus enhancing the probability of photodissociation of the ions and facilitating the confinement of the fragment ions. 
     FIG. 7B is a side perspective view of another dissociation cell/laser diode array system  100  in which a power conductor  116  of the laser diode array systems  114  is wound helically around the outer structure  110 . Winding the power conductor  116  helically around the outer structure  110 , when the outer structure  110  is not ferro-magnetic, produces an axial magnetic field when current passes through the power conductor  116 . The magnetic field produces a “magnetic bottle” effect that constrains the ions along the central longitudinal axis (not shown) of the quadrupole structure  106 . This can be advantageous because the laser radiation is focused along the central longitudinal axis of the quadrupole structure  106 , thus enhancing the probability of photodissociation of the ions. 
     It should be emphasized that the above-described embodiments of the present invention, particularly, any “preferred” embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiment(s) of the invention without departing substantially from the principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.