Abstract:
A particle inlet system comprises a first chamber having a limiting orifice for an incoming gas stream and a micrometer controlled expansion slit. Lateral components of the momentum of the particles are substantially cancelled due to symmetry of the configuration once the laminar flow converges at the expansion slit. The particles and flow into a second chamber, which is maintained at a lower pressure than the first chamber, and then moves into a third chamber including multipole guides for electromagnetically confining the particle. The vertical momentum of the particles descending through the center of the third chamber is minimized as an upward stream of gases reduces the downward momentum of the particles. The translational kinetic energy of the particles is near-zero irrespective of the mass of the particles at an exit opening of the third chamber, which may be advantageously employed to provide enhanced mass resolution in mass spectrometry.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under Contract No. DE-AC05-00OR2725 awarded by the U.S. Department of Energy. The government has certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a particle inlet system for delivering near-zero kinetic energy particles into vacuum environment, which may contain an analytical instrument such as a mass spectrometer, and methods of operating the same. 
     BACKGROUND OF THE INVENTION 
     Whenever a particle or molecule is expanded into vacuum, the expansion imparts translational kinetic energy into the particle that monotonically increases with mass. For some analytical instruments that operate under vacuum, such translational kinetic energy may pose limitations on the capability of the analytical instrument. This is particularly true of mass spectrometers, in which the initial translational kinetic energy competes with the electric and magnetic fields of the mass spectrometer such that the instrumental resolution is adversely affected by the translational kinetic energy that the particle acquires in the process of expansion into vacuum. 
     The greater the mass of the particle, the greater the expansion induced kinetic energy. But the energy imparted to the particle through the electromagnetic field is proportional only to the charge of the particle and the magnitude of the electrical field, and is independent of the mass of the particle. As the mass of the particle increases, the effect of the expansion induced kinetic energy competes with, and eventually overwhelms, the effect of the electrical potential in the mass spectrometer that is applied to define the trajectory of charged particles. For this reason, it is very difficult to measure the mass of the large molecules or particles, e.g., molecules or particles having a molecular weight of 10 kDa, by mass spectrometry. 
     A prior art solution to this problem, as disclosed by U.S. Pat. No. 6,972,408 to Reilly, provides mass-dependent slowing of particles, i.e., the particles are slowed for a limited range of particle mass. The size or mass of the particles effectively slowed depends on the pressure of the reverse jet expansion. 
     In view of the above, there exists a need for a particle inlet system into the vacuum environment that provides a reduction of expansion-induced kinetic energy with a reduced mass dependence, and methods of operating the same. 
     Further, there exists a need for a particle inlet system into vacuum environment that provides a large range of particles masses to be slowed for subsequently introduction into the vacuum environment such as a mass spectrometer, and methods of operating the same. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the needs described above by providing a particle inlet system in a configuration that permits a large range of particle masses to be slowed for subsequent introduction into the vacuum environment. 
     According to the present invention, a particle inlet system comprises a first chamber having a limiting orifice for an incoming gas stream and a micrometer controlled expansion slit having a center concentric with the center of a micrometer shaft. The laminar flow has a 180° rotational symmetry at the expansion slit so that lateral components of the momentum of the particles are substantially cancelled once the laminar flow converges at the expansion slit. The particles flow into a second chamber, which is maintained at a lower pressure than the first chamber, and then moves into a third chamber including multipole guides for electromagnetically confining the particle. The third chamber is generally maintained at a positive pressure relative to the second chamber. The vertical and radial momentum of the particles descending through the center of the third chamber is reduced by collisions with the buffer gas until their motion becomes random. These particles are said to be stopped and are free of their expansion-induced kinetic energy. If the particles have a charge their motion will then be defined by the applied electric fields of the multipole and the endcap electrodes. These particulate ions can then be collimated with a multipole guide or trapped with potentials applied to the endcap electrodes and subsequently injected on-demand into a mass spectrometer. Under these conditions, the motion of the particulate ions is completely define by the applied fields. As such their masses can then be measured with accuracy and resolution that is define by the limitations of the mass analyzer and not the expansion-induced kinetic energy. The advantage of this inlet is that it permits an extraordinarily large range of particle sizes or masses to delivered to the mass spectrometer without the initial expansion-induced kinetic energy. 
     According to an aspect of the present invention, a particle inlet system for vacuum instrumentation is provided. The particle inlet system comprises: 
     a first chamber having a gas inlet orifice and an expansion slit located over a plate containing a first opening, wherein a height of the expansion slit is adjustable in a direction along an direction perpendicular to a flat surface of the plate; 
     a second chamber connected to the first chamber at the first opening and having a second opening located directly underneath the first opening; and 
     a vacuum pump connected to, and configured to pump on, the second chamber. 
     A third chamber may be connected to the second chamber at the second opening. 
     In one embodiment, the first opening has a shape with a 180 degree rotational symmetry around an axis perpendicular to the flat surface. 
     In another embodiment, the particle inlet system further comprises a micrometer, wherein a spindle of the micrometer is located over the first opening and a thimble of the micrometer is located outside the first chamber. 
     In even another embodiment, the particle inlet system further comprises an expansion chamber located between the first chamber and the second chamber and including first-chamber-side openings and at least one second-chamber-side opening, wherein said first-chamber-side openings are located on sidewalls of said expansion chamber with a 360/n degree rotational symmetry, wherein n is an integer greater than 1. The at least one second-chamber-side opening may have a 360/m degree rotational symmetry about a same axis of rotational symmetry as the first-chamber-side openings, wherein m is an integer greater than 1. 
     In yet another embodiment, the particle inlet system fifth comprises a buffer gas inlet connected directly to the third chamber. 
     In still another embodiment, the particle inlet system further comprises: 
     a fourth chamber connected to the third chamber through a third opening, wherein the third opening is located on an opposite side of the second opening on the third chamber; and 
     another vacuum pump connected to, and configured to pump on, the fourth chamber. 
     According to another aspect of the present invention, a mass spectrometry system is provided, which comprises: 
     a first chamber having a gas inlet orifice and an expansion slit located over a plate containing a first opening, wherein a height of the expansion slit is adjustable in a direction along an direction perpendicular to a flat surface of the plate; 
     a second chamber connected to the first chamber at the first opening and having a second opening located directly underneath the first opening; 
     a vacuum pump connected to, and configured to pump on, the second chamber; 
     a third chamber having a third opening and connected to the second chamber at the second opening; 
     a fourth chamber connected to the third chamber at the third opening; and 
     a mass spectrometer located in the fourth chamber. 
     In one embodiment, the mass spectrometry system further comprises a micrometer, wherein a spindle of the micrometer is located over the first opening and a thimble of the micrometer is located outside the first chamber. 
     In another embodiment, the first opening, the second opening, and the third opening are aligned on a same axis. 
     In even another embodiment, the mass spectrometry system further comprises a micrometer, wherein an axis of the spindle of the micrometer is coincidental with the same axis. 
     According to yet another aspect of the present invention, a method of operating a particle inlet system is provided, which comprises: 
     providing a particle inlet system including a first chamber having a gas inlet orifice and an expansion slit located over a plate containing a first opening, a second chamber connected to the first chamber at the first opening and having a second opening located directly underneath the first opening, and a third chamber connected to the second chamber at the second opening; 
     inducing a laminar flow of particles within the first chamber, wherein the first chamber provides a 180 degree rotational symmetry about a center of the first opening in a pattern of the laminar flow at the expansion slit; and 
     flowing a buffer gas into the third chamber, wherein the particles are slowed within the third chamber upon entry through the second opening into the third chamber. 
     In one embodiment, the method further comprises maintaining the first chamber at a first pressure and the second chamber at a second pressure, wherein the second pressure is lower than the first pressure. 
     In another embodiment, the particles flow into a fourth chamber through a third opening in the third chamber, wherein the second opening is located in a first chamber wall of the third chamber, wherein the third opening is located on a second chamber wall of the third chamber located on an opposite side of the first chamber wall, and wherein the fourth chamber contains at least one vacuum instrumentation. 
     In even another embodiment, the method further comprises adjusting a first pressure of the first chamber by changing a height of the expansion slit. 
     In yet another embodiment, the particle inlet system further comprises a micrometer, a spindle of the micrometer is located over the first opening and a thimble of the micrometer is located outside the first chamber, and the method further comprises adjusting a first pressure of the first chamber by adjusting a distance between the spindle and the plate. 
     In still another embodiment, the method further comprises guiding the particles within the third chamber with a multipole ion guide located in the third chamber. 
     In a further embodiment, the method further comprises altering speed or trajectory of the particles within the third chamber by an electromagnetic field generated by at least one electrode located within the third chamber. 
     According to still another aspect of the present invention, another particle inlet system for vacuum instrumentation is provided. The particle inlet system comprising: 
     a first chamber including a gas inlet orifice, a first opening, and a plurality of plates, wherein each of the plurality of plates has a plate opening therein and is located between the gas inlet orifice and the first opening, wherein the gas inlet orifice, an entirety of the plate openings, and the first opening are coaxially aligned; 
     a second chamber connected to the first chamber at the first opening, having a second opening, and containing a multipole ion guide and, wherein the first opening and the second opening are aligned to a center axis of the multipole ion guide; and 
     a conical jet nozzle having a ring-shaped opening around the second opening, wherein the conical jet nozzle concentrically points toward the center axis of the multipole ion guide; 
     In one embodiment, the particle inlet system further comprises a jet nozzle housing embedding the conical jet nozzle, wherein the jet nozzle housing includes an upper plate exposed to the second chamber, a lower plate separated from the upper plate by the conical jet nozzle, and a toroidal outer frame adjoined to the upper plate and the lower plate and enclosing a toroidal gas chamber radially connected to the conical jet nozzle. 
     In another embodiment, the particle inlet system further comprises: 
     a third chamber connected to the second chamber through the second opening; and 
     a vacuum pump connected to, and configured to pump on, the third chamber. 
     In yet another embodiment, the particle inlet system further comprises at least one electrode containing an electrode hole aligned to the center axis and located within the second chamber. 
     According to a further aspect of the present invention, a method of operating a particle inlet system for vacuum instrumentation is provided. The method comprises: 
     providing a directional particle beam from a first chamber into a second chamber, wherein the first chamber comprises a gas inlet orifice, a first opening, and a plurality of plates having a plate opening therein and located between the gas inlet orifice and the first opening, wherein the gas inlet orifice, an entirety of the plate openings, and the first opening are coaxially aligned, and wherein particles move from the gas inlet orifice through the plate openings and to the first opening; 
     focusing the direction particle beam in the second chamber with a multipole ion guide located within the second chamber, wherein the directional particle beam moves through the multipole ion guide and exits the second chamber through a second opening into a third chamber; and 
     providing a reverse jet through a conical jet nozzle having a ring-shaped opening around the second opening, wherein momentum of the directional particle beam is counterbalanced by momentum of the reverse jet, whereby the directional particle beam loses kinetic energy before entry into the third chamber. 
     In one embodiment, the method further comprises pumping the second chamber with a vacuum pump, wherein the second chamber is maintained at a lower pressure relative to the first chamber. 
     In another embodiment, the vacuum instrumentation includes a mass spectrometer located in the third chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical cross-sectional view of a first exemplary particle inlet system comprising a first chamber  30 , a second chamber  60 , a third chamber  80 , and a fourth chamber  80  housing vacuum instrumentation  95  according to a first embodiment of the present invention. 
         FIG. 2  is a magnified view of the first exemplary particle inlet system of the first chamber  30 , the second chamber  60 , and the third chamber  80  according to the first embodiment of the present invention. The fourth chamber  80  is partially shown in  FIG. 2 . 
         FIG. 3  is a magnified vertical cross-sectional view of the first exemplary particle inlet system around a plate  54  containing a first opening  39  and a second opening  77  according to the first embodiment of the present invention. 
         FIGS. 4A and 4B  are exemplary shapes for the plate  54  and the first opening  39  contained therein in the first exemplary particle inlet system according to the first embodiment of the present invention. 
         FIG. 5A  is a top-down view of an exemplary expansion chamber that may be employed instead of the first opening  39  and the micrometer of  FIGS. 1-4 .  FIG. 5B  is a vertical cross-sectional view of the exemplary expansion chamber of  FIG. 5A .  FIG. 5C  is an alternate vertical cross-sectional view of the exemplary expansion chamber of  FIG. 5A . 
         FIG. 6  is a vertical cross-sectional view of a second exemplary particle inlet system comprising a first chamber  130 , a second chamber  180 , and a third chamber  290  according to a second embodiment of the present invention. 
         FIG. 7A  is a side view of a jet nozzle housing according to the second embodiment of the present invention.  FIG. 7B  is a vertical cross-sectional view of the jet nozzle housing according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As stated above, the present invention relates to a particle inlet system for delivering near-zero kinetic energy particles into vacuum environment, which may contain an analytical instrument such as a mass spectrometer, and methods of operating the same, which are now described in detail with accompanying figures. It is noted that like and corresponding elements mentioned herein and illustrated in the drawings are referred to by like reference numerals. It is also noted that proportions of various elements in the accompanying figures are not drawn to scale to enable clear illustration of elements having smaller dimensions relative to other elements having larger dimensions. 
       FIGS. 1-3  illustrate a first exemplary particle inlet system according to a first embodiment of the present invention.  FIGS. 1-3  are vertical cross-sectional views with different magnifications. Specifically,  FIG. 1  shows the entirety of the first exemplary particle inlet system including a first chamber  30 , a second chamber  60 , a third chamber  80 , and a fourth chamber  80  housing vacuum instrumentation  95 .  FIG. 2  shows a magnified view of the first chamber  30 , the second chamber  60 , and the third chamber  80 .  FIG. 3  shows the first exemplary particle inlet system around a plate  52  containing a first opening  39  and a second opening  77 . 
     The first exemplary particle inlet system is employed to deliver near-zero kinetic energy particles into the fourth chamber  80  which houses the vacuum instrumentation  95 . The vacuum instrumentation  95  may be any type of vacuum compatible instrument, and may be an analytical device. Preferably, the vacuum instrumentation  95  is a vacuum compatible instrument that benefits from low kinetic energy of particles. Particularly, the vacuum instrumentation  95  may be a mass spectrometer, of which the resolution is enhanced when the kinetic energy of the particles is lowered. When the kinetic energy of the particles is near-zero as in the present invention, the mass spectrometer provides high resolution even for particles having a high atomic mass, e.g., over 200 kDa. 
     An aerosol of particles is introduced with a carrier gas from a gas inlet assembly  10  through a gas inlet orifice  17  into the first chamber  30  of the first exemplary particle inlet system. Preferably, the gas inlet orifice  17  is a flow limiting orifice. The dimension, e.g., a diameter, of the gas inlet orifice  17  may be from about 10 μm to about 1 mm, and typically from about 30 μm to about 300 μm, although lesser and greater dimensions are contemplated herein also. The particles may, or may not, be charged when admitted into the first chamber  30 . In case the vacuum instrumentation  95  comprises a mass spectrometer, the particles are preferably electrically charged prior to entry into the first chamber  30 . The aerosol of particles expands into the first chamber  30  at a reduced pressure, i.e., at a lower pressure than the pressure at the gas inlet assembly  10 , which may be at an atmospheric pressure. The velocities of the particles and the carrier gas come into equilibrium in the first chamber  30 , which is also referred to as a plenum chamber, so that the particles and the carrier gas form a laminar flow. 
     The first chamber  30  is enclosed by first chamber walls  32 , and is connected to the gas inlet assembly  10  through the gas inlet orifice  17  and to the second chamber  60  through a first opening  39  (See  FIG. 3 ), which is located within a plate  54 . The plate  54  may be embedded in one of the first chamber walls  32 . Other than the gas inlet orifice  17  and the first opening  39 , the first chamber  30  is vacuum tight. 
     A micrometer  100  is provided on the first chamber  30 . The micrometer  100  includes a thimble  56  located on the outside of the first chamber and a spindle  52  located inside the first chamber  30 . The spindle  52  is vertically movable in the direction of the axis of the spindle  52  by tuning of the thimble  56  of the micrometer  100 . The spindle  52  is located over the first opening  39 , and the end surface of the spindle  52  is parallel to the surface of the plate  54  so that the first opening may be sealed by the movement of the spindle  52 . The spindle  52  may be a cylinder of a constant horizontal cross-sectional shape, which has a 180 degree rotational symmetry. Preferably, the spindle  52  comprises a circular cylinder. 
     An adjustable expansion slit  37  is formed between the face of the plate  54  toward the first chamber  30  and the end surface of the spindle  52  when the setting of the thimble  56  of the micrometer  100  does not make the end face of the spindle  52  directly contact the face of the plate  54 , thereby sealing the first chamber  30  from the second chamber  60 . The height of the “adjustable” expansion slit  37  is adjustable by sliding the spindle  52  of the micrometer  100  toward, or away from, the face of the plate  54 . The maximum distance that the spindle  52  may travel vertically may be from about 3 mm to about 3 cm, and typically from about 6 mm to about 1.5 cm, although lesser and greater distances are contemplated herein also. The distance resolution of the distance of the spindle  52  from the face of the plate  54 , i.e., the height of the adjustable expansion slit  37 , is preferably on the order of one millimeter. The control of the height of the adjustable expansion slit  37  enables a precise control of the pressure drop across the adjustable expansion slit  37 , which is an expansion orifice, over a wide pressure range. While cylindrical symmetry of the adjustable expansion slit  37  and the first opening  39  is preferred, the present invention may be practiced with different geometric shapes as long as a 180 degree rotational symmetry is provided to the flow of particles and carrier gas molecules. 
     The adjustable “expansion” slit  37  induces expansion of the aerosol of particles since the second chamber  60  is pumped by a second chamber vacuum pump  66 , which is mounted to second chamber walls  62  through a second chamber mounting flange  64  and a second chamber gate valve  63 , while no pump is directly mounted on the first chamber  30 . To reduce load on the second chamber vacuum pump  66 , the second chamber gate valve  63  is typically operated at a partially open state. The pressure of the first chamber  30 , which is herein referred to as a first pressure, is higher than the pressure of the second chamber  60 , which is herein referred to as a second pressure. The aerosol of particles, which form a laminar flow in the first chamber  30 , expands as it flows into the second chamber  60 . Typically, the first pressure is maintained in the range from about 70 mTorr to about 1 atm, and the second pressure is maintained in the range from about 1 mTorr to about 100 mTorr, although lesser and greater values are contemplated for the first pressure and the second pressure also. The first pressure and the second pressure may be measured by pressure gauges. The adjustable expansion slit  37  is an inward expansion slit since the laminar flow of the particles and carrier gases in the first chamber  30  expands as they cross over the adjustable expansion slit  37  from the outside of the circumference that defines the adjustable expansion slit  37  to the inside of the circumference. 
     The adjustable expansion “slit”  37  limits flow of the aerosol of the particles, and has a shape of a slit having a geometry in which the height of the slit is less than the circumference of the slit. In case the spindle  52  has the shape of a circular cylinder, the adjustable expansion slit  52  has a circular circumference having the same diameter as the diameter of the spindle  52 . In other words, the adjustable expansion slit  37  has a shape of a sidewall surface of a circular cylinder having a radius equal to a radius of the spindle  52  of the micrometer  100 . The diameter of the spindle may be from about 1.5 mm to about 15 cm, and typically from about 6 mm to about 4 cm, although lesser and greater diameters are also contemplated herein. In this case, the adjustable expansion slit  37  is axially symmetric, i.e. has an axial symmetry around the axis of the spindle  52 , and has a toroidal shape. The aerosol of particles undergoes an axially symmetric inward expansion as it passes from the first chamber  30  through the adjustable expansion slit  37 . The expansion then rebounds off of itself and undergoes another expansion in the normal direction toward the first opening  39 . The particles in the expansion also rebound regardless of size and are slowed in the radial direction but may rebound more than once. Eventually, enough axial momentum is imparted for them to escape through opening  39  or deposit on a surface. The direction of the movement of the particles is schematically illustrated in  FIG. 3  by dotted arrows. 
     Particles and carrier gas molecules expanding through one side of the adjustable expansion slit  37  encounter other particles and other carrier gas molecules expanding through the opposite side of the adjustable expansion slit  37 . The lateral momentum of the particles and the carrier gas molecules cancel out as they converge at the center of the adjustable expansion slit  37  in the shape of the toroid. The lateral momentum of the particles as they enter the second chamber  60  through the first opening  39  is thus substantially decreased. Depending on the vertical momentum of the particles after the flow of the particles and the carrier gas molecules collide at the axis of the spindle  52  of the micrometer  100 , the particles are entrained into a flow of the particles in the direction orthogonal to the radius of the adjustable expansion slit  37 , i.e., orthogonal to the end surface of the spindle  52 . Due to the loss of all lateral momentum, particles after the expansion at the adjustable expansion slit  37  have a much reduced velocity compared to the particles in the first chamber  30 . 
       FIG. 4A  shows a top-down view of a first exemplary shape for the plate  54 , the first opening  39 , and the areal projection  52 ′ of the spindle  52  in the first exemplary particle inlet system.  FIG. 4B  shows a top-down view of a second exemplary shape for the plate  54 , the first opening  39 , and the areal projection  52 ′ of the spindle  52  in the first exemplary particle inlet system. 
     Preferably, the first opening  39  has a shape with a 180 degree rotational symmetry around an axis perpendicular to the face, which is a flat surface of the plate  54 . The 180 degree rotational symmetry insures that the opening does not introduce any symmetry breaking as the particles and the carrier gas molecules collide at the axis of the spindle  52  of the micrometer  100 , thereby cancellation of lateral momentum of the particles and the carrier gas molecules is near complete. The shape of the first opening  39  may be a circle, an ellipse, a square, a rectangle, a polygon having an even number of sides, or any other geometric shape having a 180 degree rotational symmetry around an axis through the center of the geometric shape. Preferably, the shape of the first opening  39  is a circle having a diameter, which may be from about 1 mm to about 10 cm, and typically from about 3 mm to about 3 cm, although lesser and greater diameters are contemplated herein also. 
     The center of the geometric shape coincides with the axis of the spindle  52  of the micrometer  100 . In other words, the first opening  39  and the spindle  52  of the micrometer  100  are coaxially aligned. 
     In a variation of the first embodiment of the present invention, the first opening  39  and the micrometer may be replaced by an expansion chamber having two sets of openings.  FIG. 5A  is a top-down view of an exemplary structure for an expansion chamber  330 .  FIGS. 5B and 5C  are alternate vertical cross-sectional views of the exemplary structure for the expansion chamber  330  of  FIG. 5A . 
     The expansion chamber  330  is located between the first chamber  30  and the second chamber  60 , and provides a path for particles to pass from the first chamber  30  to the second chamber  60 . First-chamber-side openings  329  are located on sidewalls of the expansion chamber  330  with a 360/n degree rotational symmetry to induce cancellation of average lateral momentum of the particles that enter the expansion chamber  330 , in which n is an integer greater than 1. For example, the expansion chamber  330  may have two first-chamber-side openings  329  located on opposite ends, in which case the number n is equal to 2. The expansion chamber  330  may have three first-chamber-side openings  329  separated by 120 degrees therebetween, in which case the number n is equal to 4. In general, the expansion chamber  330  may have n of first-chamber-side openings  329 , which are separated by 360/n degrees therebetween and the number n is any integer greater than 1. 
     Further, the expansion chamber  300  may have any additional set of first-chamber-side openings  329  provided that each of the first-chamber-side openings  329  have a 360/n′ degree rotational symmetry, in which n′ is an integer greater than 1. n′ may, or may not, be the same as n. 
     The expansion chamber  330  also has at least one second-chamber-side opening  331 , which provides a path for particles to move from inside the expansion chamber  330  to the second chamber  60 . The number of holes in the at least one second-chamber-side opening  331  may be 1, or a number greater than 1. Preferably, the shape of the at least one second-chamber-side opening  331  has a 360/m degree rotational symmetry about the same axis of the rotational symmetry for the first-chamber-side openings  329 . m is an integer greater than 1. The shape of the at least one second-chamber-side opening  331  may have an axial symmetry about the same axis of the rotational symmetry for the first-chamber-side openings  329 . The dimensions of the at least one second-chamber-side opening  331  may be about the same as the dimensions of the first opening  39  described above. 
     The particles move through the second chamber  60  into a third chamber  80  through a second opening  77  provided within one of third chamber walls  72  that enclose the third chamber  80 . The distance between the first opening  39  and the second opening  77  may be from about 1 mm to about 15 cm, and typically from about 5 mm to about 5 cm, although lesser and greater distances are contemplated herein also. The shape of the second opening  77  may, or may not, have a 180 degree rotational symmetry. Preferably, the shape of the second opening  77  has a 180 degree rotational symmetry. The center of the second opening  77 , if definable, is preferably aligned to the center of the first opening  39 . The size of the second opening  77  is greater than the size of the first opening. The dimension, e.g., the diameter, of the second opening  77  may be from about 3 mm to about 30 cm, and typically from about 1 cm to about 10 cm, although lesser and greater thicknesses are contemplated herein also. 
     The particles subsequently move through the third chamber  80  to a third opening  87  located in another of the third chamber walls  72 . The third opening  87  is located on an opposite side of the second opening  77 . The first opening  39 , the second opening  77 , and the third opening  87  may be located on a same axis, which preferably coincides with the axis of the spindle  52  of the micrometer  100 . A fourth chamber  90  is connected to the third chamber  80  through the third opening  87 . The fourth chamber  90  comprises vacuum instrumentation  95 , which may be, for example, a mass spectrometer. A fourth chamber vacuum pump  96  is connected to fourth chamber walls  92  through a fourth chamber mounting flange  94  and a fourth chamber gave valve  93 . Typically, the fourth chamber gate valved  93  is operated at a fully open state to provide high vacuum to the fourth chamber  90 . 
     For the purposes of application of the first exemplary particle inlet system in a mass spectrometry system, charged particles are employed for injection into the first chamber  30 , and subsequent flow into the second chamber  60 , the third chamber  80 , and the fourth chamber  90 . A multipole ion guide  86  is provided within the third chamber  80 . The multipole ion guide  86  guides comprises a plurality of poles surrounding a central cavity through which charged ions move. A set of electrical feedthroughs (not shown) are connected to the electrodes of the multipole ion guide  86 . The central cavity in the multipole ion guide  86  is preferably aligned to an axis connecting the second opening  77  to the third opening  87 , i.e., the center axis of the multipole ion guide  86  coincides with axis that connects the second opening  77  to the third opening  87 . By applying a time dependent electrical potential to the poles with appropriate phase differences, the ions are dynamically confined around the central cavity. The frequency, the amplitude, and the phase of the electrical potential depend on the geometry of the multipole ion guide  86 . Operational principles of multipole ion guides are known in the art. The charged particles move down the central cavity of the multipole ion guide around the axis of the multipole ion guide  86 . 
     The charged particles that move into the third chamber  80  may still have some lateral momentum since the cancellation of the lateral momentum during convergence of the charged particles at the axis of the adjustable expansion slit  37  is statistical. In other words, while the average lateral momentum of the particles is zero, the individual particles may have a distribution of non-zero lateral momentum. Thus, the charged particles entering the center cavity of the multipole ion guide  86  may be somewhat divergent, i.e., not collimated. However, the electromagnetic field of the multipole ion guide  86  focuses the charged particles as a directional beam along the central axis of the multipole ion guide  86 . The diameter of the central cavity of the multipole ion guide  86 , i.e., the diameter of a maximal circle that fits within the central cavity of the multipole ion guide  86 , may be from about 1 mm to about 1 m, and typically from about 5 mm to about 20 cm, although lesser and greater diameters are contemplated herein also. In practice, a multipole ion guide  86  having a large diameter tends to provide greater stopping distances to any divergent charged ions and capture heavier charged particles. 
     Control of the expansion of particles from the first chamber  30  through the adjustable expansion slit  37 , the first opening  39 , the portion of the second chamber  60  between the first opening  39  and the second opening  77 , the second opening  77 , and into the central cavity of the multipole ion guide  86  in the third chamber  80  is accomplished by optimizing the geometry of the adjustable expansion slit  37 . Such optimization may be done with fluid dynamics calculations. The primary control variables of this type of calculation are the lateral area of the adjustable expansion slit  37  for the inward expansion and the dimension, e.g., the diameter, of the third chamber  80 . The height and the circumference of the adjustable expansion slit  37  and the area of the first opening  39 , which is an expansion orifice, can be adjusted to optimize charged particle capture in the third chamber  80 . 
     A buffer gas inlet  73  is provided on one of the third chamber walls  72  located on the same side of the third chamber  80  as the third opening  87 , which is located on the opposite side of another of the third chamber walls  72  containing the second opening  77 . A buffer gas, which may comprise H 2 , He, Ne, Ar, Kr, N 2 , etc., are flowed through a gas flow control device  74  through the buffer gas inlet  73  into the third chamber  80 . The gas flow control device  74  may be a mass flow controller, an adjustable valve, or a restriction valve. The third chamber  80  is maintained at a third pressure, which is slightly higher than the second pressure of the second chamber  60 . The third pressure may be from about 5 mTorr to about 300 mTorr, and preferably from about 1 mTorr to about 100 mTorr, although lesser and greater values for the third pressure are contemplated herein also. The third pressure may be inferred from measurement on the second pressure. 
     The geometry of the structures within the third chamber  80  is optimized so that the buffer gas flows toward the second opening  77 . For example, the dimensions of the third opening  87  are set to be smaller than the dimensions of the second opening  77 . For example, the dimensions, e.g., the diameter, of the third opening  87  may be from about 0.6 mm to about 6 cm, and typically from about 1.8 mm to about 2 cm, so that the buffer gas exists the third chamber predominantly through the second opening  77  instead of the third opening  87 . The charged particles that move down along the central cavity of the multipole ion guide  86  are slowed within the third chamber  80  upon entry through the second opening  77  into the third chamber  80 . The buffer gas provides an upward momentum transfer to the charged particles that move down the central cavity of the multipole ion guide  86  toward the third opening  87 . 
     Once captured in the multipole ion guide  86  as a focused particle beam, the charged particles undergo many collisions with the buffer gas during descent down the center cavity of the multipole ion guide  86 . In other words, collisions of the charged particles with the buffer gas inside the third chamber  80  abate the forward motion, or a downward motion, of the charged particles, while the multipole ion guide  86  collimates the charged particles along the central axis of the multipole ion guide  86 . As the kinetic energy is taken away from the charged particles, the trajectory of the charged particles converge on the axis of the multipole ion guide as the charged particles, i.e., ions, loses kinetic energy and move to the middle of the center cavity of the multipole ion guide  86 . 
     Preferably, at least one electrode, to which electric potential is applied, is provided in the third chamber  80  to facilitate the convergence, and the subsequent accumulation, of the charged particles to the middle of the center cavity of the multipole ion guide  86 . For example, a first end cap electrode  82  may be formed near the second opening  77 , and a second end cap electrode  84  may be formed near the third opening  87 . Each of the first end cap electrode  82  and the second end cap electrode  84  contains a hole to allow passage of the charged particles therethrough. The holes of the first end cap electrode  82  and the second end cap electrode  84  are aligned to the axis connecting the center of the second opening  77  with the center of the third opening  87 , which may be coincident with the axis of the multipole ion guide  86 . 
     A first high transmittance conductive mesh  83  and a second high transmittance conductive mesh  85  may be provided adjacent to the openings in the first end cap electrode  82  and the second end cap electrode  84 , respectively. The first and second high transmittance conductive meshes ( 83 ,  85 ) encompass at least the area of the openings of the first end cap electrode  82  and the second end cap electrode  84 , respectively. Preferably, the same electric potential is applied to the first high transmittance conductive mesh  83  as to the first end cap electrode  82 , and the same electric potential is applied to the second high transmittance conductive mesh  85  as to the second end cap electrode  84 . The first and second high transmittance conductive meshes ( 83 ,  85 ) flatten the electric field at the ends of the multipole ion guide  86 . The ratio of the area between the wires of the first and second high transmittance conductive meshes ( 83 ,  85 ) and the area occupied by the wires of the first and second high transmittance conductive meshes ( 83 ,  85 ) is kept as high as possible to provide a high transmittance. 
     Optionally, charged particles, i.e., ions, may be mass selected in the multipole ion guide  86  so that a larger concentration of the charged particles of interest may be delivered into the fourth chamber  90  through the third opening  87 . Such a feature is advantageous if analysis of charged particles with a large atomic mass is performed in the fourth chamber  90 . For example, the analysis may be protein analysis by mass spectroscopy, in which the concentration of various protein molecules may vary by as much as six orders of magnitude. 
     Preferably, the charged particles are extracted from the multipole ion guide  86  by changing the electrical potential on the first and second end cap electrodes ( 82 ,  84 ). In this case, a large diameter is preferred for the multipole ion guide  86  because such a large diameter enables deep penetration of the electrical field generated by the first and second end cap electrodes ( 82 ,  84 ), which is referred to as an end cap electric field, into the multipole ion guide  86 . Such deep penetration of the end cap electric field permits efficient extraction of the charged particles from the multipole ion guide  86  with excellent control of the kinetic energy of the charged particles. 
     Thus, charged particles with extremely low kinetic energy may be selectively extracted through the third opening  87  into the fourth chamber  90 . In case the vacuum instrumentation  95  comprises a mass spectrometer, well-controlled injection of low-kinetic energy charged particles into the fourth chamber  90  enables precise control of the trajectory of the charged particles by the electromagnetic field of the mass spectrometer even for charged particles with a high atomic mass. When the trajectories of the charged particles are completely defined by the applied electromagnetic field, accurate high resolution mass measurement may be made for charged particle having a high mass-to-charge ratio. 
     Employing a multipole ion guide  86  having a large radius provides an additional benefit of accumulation of a large number of charged particles. Such an accumulation enables a higher flux of charged particles into the fourth chamber so that measurement of a large range of concentrations for the particle species may be performed. 
     The capture efficiency, or the ratio of the flux of the charged particles through the third opening  87  to the flux of the charged particles through the first opening  39 , is determined by several factors including the radial divergence angle of the first chamber walls  32  near the first opening  39 , the velocity distribution of the charged particles, the mass-to-charge ratio of the charged particles, the frequency and voltages of the electrical signal applied to both the multipole ion guide  86  and to the first and second end cap electrodes ( 82 ,  84 ), and buffer gas pressure. The pressure inside the third chamber  80  may be adjusted by adding additional gas to the third chamber and/or throttling the second chamber vacuum pump  66  to optimize the ion capture efficiency. In practice, using large radius multipoles permits greater trapping of larger particles. The combination of the control of the expansion of the laminar flow at the adjustable expansion slit  37 , the gas pressure in the third chamber  80 , and the radius of the multipole ion guide  86  are key elements in achieving efficient capture of a large quantity of charged particles, i.e., ions, of any size. 
     The unique feature of this method of slowing down the charged particles is that there is no mass dependence for slowing the particles down. The prior art method described in U.S. Pat. No. 6,972,408 had a reverse jet pressure dependence of retardation of particle speed, in which particles within only a relatively narrow range of atomic mass are slowed. The present invention eliminates such a problem since the mechanism for the slowing of the charged particles is by a momentum transfer by the buffer gas. The present invention permits the capture and storage of a large quantity of charged particles over a vast range of mass-to-charge ratios for a subsequent controlled injection into a fourth chamber  90 , which contains vacuum instrumentation  95 . In case the vacuum instrumentation comprises a mass spectrometer, an accurate high resolution measurement of atomic mass of the charged particles over an enormous range of atomic mass is enabled well above 200 kDa, and even beyond the range of 10 GDa. 
     Referring to  FIG. 6 , a vertical cross-sectional view of a second exemplary particle inlet system according to a second embodiment of the present invention is shown, which comprises a first chamber  130 , a second chamber  180 , and a third chamber  290 . The second exemplary particle inlet system is employed to deliver near-zero kinetic energy particles into the third chamber  290  which houses vacuum instrumentation  295 . The vacuum instrumentation  295  may be any type of vacuum compatible instrument, and may be an analytical device. Preferably, the vacuum instrumentation  295  is a vacuum compatible instrument that benefits from low kinetic energy of particles. Particularly, the vacuum instrumentation  295  may be a mass spectrometer, of which the resolution or sensitivity is enhanced when the kinetic energy of the particles is lowered. When the kinetic energy of the particles is near-zero as in the present invention, the mass spectrometer provides high resolution even for particles having a high atomic mass, e.g., over 200 kDa. 
     An aerosol of particles is introduced with a carrier gas from a gas inlet assembly  110  through a gas inlet orifice  117  into the first chamber  130  of the second exemplary particle inlet system. Preferably, the gas inlet orifice  117  is a flow limiting orifice. The dimension, e.g., a diameter, of the gas inlet orifice  117  may be from about 10 μm to about 1 mm, and typically from about 30 μm to about 300 μm, although lesser and greater dimensions are contemplated herein also. The particles may, or may not, be charged when admitted into the first chamber  130 . In case the vacuum instrumentation  295  comprises a mass spectrometer, the particles are preferably electrically charged prior to entry into the first chamber  130 . The aerosol of particles expands into the first chamber  130  at a reduced pressure, i.e., a lower pressure than the pressure at the gas inlet assembly  110 , which may be at an atmospheric pressure. 
     The first chamber  130  is enclosed by first chamber walls  132 , and is connected to the gas inlet assembly  110  through the gas inlet orifice  117  and to the second chamber  180  through a first opening  139 , which is located on one of first chamber walls that is located on the opposite side of the gas inlet assembly  110 . Other than the gas inlet orifice  117  and the first opening  139 , the first chamber  130  is vacuum tight. 
     The second chamber  180  is connected to the first chamber  130  through the first opening  139 . The second chamber  180  is pumped by a second chamber vacuum pump  176 , which is mounted to second chamber walls  172  through a second chamber mounting flange  174  and a second chamber gate valve  173 , while no pump is directly mounted on the first chamber  130 . To reduce load on the second chamber vacuum pump  176 , the second chamber gate valve  173  is typically operated at a partially open state. The pressure of the first chamber  130 , which is herein referred to as a first pressure, is higher than the pressure of the second chamber  180 , which is herein referred to as a second pressure. Typically, the first pressure is maintained in the range from about 1 Torr to about 5 Torr, and the second pressure is maintained in the range from about 1 mTorr to about 100 mTorr, although lesser and greater values are contemplated for the first pressure and the second pressure also. 
     A third chamber vacuum pump  276  is connected to third chamber walls through a third chamber mounting flange  274  and a third chamber gate valve  273 . Typically, the third chamber gate valve  273  is operated at a finally open state to provide high vacuum to the third chamber  290 . 
     The first chamber  130  constitutes an aerodynamic lens system that forms a focused aerosol beam from the particles injected through the gas inlet orifice  117 . A plurality of plates  131 , each having a plate opening  133 , is located between the gas inlet orifice  117  and the first opening  139 . The gas inlet orifice  117 , an entirety of the plate openings  133 , and the first opening  139  are coaxially aligned. A laminar flow is formed in the first chamber  130  according to fluid dynamics of the particles and the carrier gas molecules. Since each of the plurality of plates  131  provides a boundary for the laminar flow, the flow of the charged particles becomes a tightly-collimated beam by the time the particles reach the first opening  139 . Thus, the aerodynamic lens system, formed by the geometry of the first chamber  130 , delivers a highly directional beam of particles into the second chamber  180 . The laminar flow is controlled by the geometry of the first chamber  130  and the pressure of the second chamber  180 . The distance between the gas inlet orifice  117  and the first opening  139  may be from about 5 cm to about 3 m, and preferably from about 15 nm to about 1 m, although lesser and greater distances are contemplated herein also. 
     The particles move into the second chamber  180  through the first opening  139 . The shape of the first opening  139  may, or may not, have a 180 degree rotational symmetry. Preferably, the shape of the first opening  139  has a 180 degree rotational symmetry. The dimension, e.g., the diameter, of the first opening  139  may be from about 0.3 mm to about 3 cm, and typically from about 1 mm to about 1 cm, although lesser and greater thicknesses are contemplated herein also. 
     The particles subsequently move through the second chamber  180  to a third opening  187  located at the center of a jet nozzle housing embedding a conical jet nozzle  212 . In the second chamber  180 , the second opening  187  is located on an opposite side of the first opening  139 . The gas inlet orifice  117 , the first opening  39 , and the second opening  187  may be located on a same axis. The third chamber  290  is connected to the second chamber  180  through the second opening  187 . The third chamber  290  comprises vacuum instrumentation  295 , which may be, for example, a mass spectrometer. A third chamber vacuum pump  276  mounted to the third chamber  290  through a third chamber mounting flange  274  provides pumping to the third chamber  290 . The third chamber  290  is maintained at a third pressure, which is less than 100 mTorr, and typically less than 10 mTorr. 
     For the purposes of application of the second exemplary particle inlet system in a mass spectrometry system, charged particles are employed for injection into the first chamber  130 , and subsequent flow into the second chamber  180  and the third chamber  290 . A multipole ion guide  186  is provided within the second chamber  180 . The multipole ion guide  186  guides comprises a plurality of poles surrounding a central cavity through which charged ions move. The structure and operation of the multipole ion guide  186  are the same as in the first embodiment of the present invention described above. 
     The charged particles that move into the second chamber  180  may still have some lateral momentum since the momentum of individual charged particles as they enter the second chamber  180  has a statistical distribution. In other words, while the average lateral momentum, i.e., the momentum in the plane perpendicular to the direction of the beam of the charged particles, of the particles is zero, the individual charged particles may have a distribution of non-zero lateral momentum. Thus, the momentum of the charged particles entering the center cavity of the multipole ion guide  186  may have a small magnitude of divergent component, i.e., a non-collimated component despite the aerodynamic lens system of the first chamber  130 . In other words, the imperfection of the aerodynamic lens system allows a finite distribution of lateral momentum in the plane perpendicular to the direction of the charged particles. 
     The electromagnetic field of the multipole ion guide  186  focuses the charged particles as a directional beam along the central axis of the multipole ion guide  86 . Any small magnitude of lateral momentum in the charged particles is lost as the charged particles travel through the second chamber  180 , and become even more collimated due to the electromagnetic field of the multipole ion guide  186 . The structure and dimensions of the multipole ion guide  186  is the same as the structure and dimensions of the multipole ion guide  86  in the first embodiment. 
     The structure of the jet nozzle housing is illustrated in  FIGS. 7A and 7B .  FIG. 7A  is a magnified side view of the jet nozzle housing as seen from the direction of the first opening  139 , e.g., from the middle of the multipole ion guide  186 .  FIG. 7B  is a magnified view of the vertical cross-sectional view of the jet nozzle housing. The jet nozzle housing comprises an upper plate  210  exposed to the second chamber  180 , a lower plate  220  separated from the upper plate  210  by the conical jet nozzle  220  and a planar separation space  214  having a constant width, and a toroidal outer frame  230  adjoined to the upper plate  210  and the lower plate  220  and enclosing a toroidal gas chamber  216 , which is radially connected to the conical jet nozzle  212  through the planar separation space  214 . 
     The conical jet nozzle  212  has a shape of a truncated cone, of which the truncated apex is coincident with a point at the center of the charged particle beam. The located of the charged particle beam is the center axis of the multipole ion guide  186 , i.e., the axis of the center cavity of the multipole ion guide  186 . The conical jet nozzle  212 , the planar separation space  214 , and the toroidal gas chamber  216  form a contiguous space. Preferably, the set of the conical jet nozzle  212 , the planar separation space  214 , and the toroidal gas chamber  216  has a cylindrical symmetry around the center axis of the multipole ion guide  186 . The second opening  187  is located at the center of the jet nozzle housing ( 210 ,  220 ,  230 ). The second opening  187 , the opening of the conical jet nozzle  212 , and the toroidal gas chamber  216  are concentric, and the center of these structures coincide with the center axis of the multipole ion guide  186 . 
     A buffer gas inlet  218  is provided on the toroidal gas chamber  216 . A buffer gas, which may comprise H 2 , He, Ne, Ar, Kr, N 2 , etc., are flowed through a gas flow control device  219  through the buffer gas inlet  218  into the toroidal gas chamber  216 . The gas flow control device  219  may be a mass flow controller, an adjustable valve, or a restriction valve. The toroidal gas chamber  216 , the planar separation spacer  214 , and the conical jet nozzle  212  are maintained at a pressure higher than the second pressure of the second chamber  180 . The pressure of the conical jet nozzle  212  may be from about 5 mTorr to about 300 mTorr, and preferably from about 10 mTorr to about 100 mTorr, although lesser and greater values for the third pressure are contemplated herein also. 
     A reverse jet of the buffer gas is provided through the conical jet nozzle  212  into the second chamber  180 . Typically, the area of the orifice of the conical jet nozzle  212  is equivalent to the area of the first opening  139 , which is the area of the nozzle provided by the aerodynamic lens system of the first chamber  130 . The buffer gas flux of the reverse jet may be adjusted so that the total momentum flux of the reverse jet of the buffer gas is equal in magnitude as, and has the opposite direction of, the total momentum flux of the charged particles in the multipole ion guide  186 . Such a setting enables reduction of the momentum of the charged particles to near zero in the multipole ion guide  186 . After a predefined collection time, the reverse jet may be temporarily stopped to permit injection of the charged particles that have been trapped in the multipole ion guide  186  to be injected into the third chamber  290 . The charged particles injected into the third chamber  290  do not have any residual expansion-induced kinetic energy regardless of mass. 
     The conical geometry of the conical jet nozzle  212  enables convergent delivery of the buffer gas on a point in the path of the charged particles in the second chamber  180 . The lateral momentum of the buffer gas is cancelled since the conical jet nozzle  212  is cylindrically symmetric about an axis defined by the charged particle beam, and as a consequence, the flow of the buffer gas into the second chamber is also cylindrically symmetric about the axis defined by the charged particle beam, which is the axis of the multipole ion guide  186 . Thus, there is no mechanism to generate an aerodynamic vortex in the second chamber  180 . 
     The buffer gas provides a net momentum transfer to the charged particles that move down the central cavity of the multipole ion guide  86  toward the second opening  187  in the direction opposite to the movement of the charged particles. The net momentum of the buffer gas in the axial direction is adjusted to almost cancel out the momentum of the charged particle beam so that the charged particles lose kinetic energy while approaching the third opening  187 . By the time the charged particles reach the third opening  187 , the kinetic energy of the charged particles is near zero. 
     Preferably, the dimensions, e.g., the diameter, of the third opening  87  are optimized to facilitate the removal of the carrier gas molecules and the buffer gas through the second chamber vacuum pump  176 . For example, the dimensions, e.g., the diameter, of the third opening  87  may be from about 0.6 mm to about 6 cm, and typically from about 1 mm to about 1 cm, so that the buffer gas exits the second chamber  180  predominantly through the second chamber vacuum pump instead of the second opening  187 . 
     Preferably, at least one electrode, to which electric potential is applied, is provided in the second chamber  180  to facilitate the convergence, and the subsequent accumulation, of the charged particles to the middle of the center cavity of the multipole ion guide  186 . For example, a first end cap electrode  182  may be formed near the first opening  139 , and a second end cap electrode  184  may be formed near the second opening  187 . Each of the first end cap electrode  182  and the second end cap electrode  184  contains a hole to allow passage of the charged particles therethrough. The holes of the first end cap electrode  182  and the second end cap electrode  184  are aligned to the axis connecting the center of the first opening  139  with the center of the second opening  187 , which may be coincident with the axis of the multipole ion guide  86 . 
     A first high transmittance conductive mesh  183  and a second high transmittance conductive mesh  185  may be provided adjacent to the openings in the first end cap electrode  182  and the second end cap electrode  184 , respectively. The first and second high transmittance conductive meshes ( 183 ,  185 ) encompass at least the area of the openings of the first end cap electrode  182  and the second end cap electrode  184 , respectively. Preferably, the same electric potential is applied to the first high transmittance conductive mesh  183  as to the first end cap electrode  182 , and the same electric potential is applied to the second high transmittance conductive mesh  85  as to the second end cap electrode  184 . The first and second high transmittance conductive meshes ( 183 ,  185 ) flatten the electric field at the ends of the multipole ion guide  186 . The ratio of the area between the wires of the first and second high transmittance conductive meshes ( 183 ,  185 ) and the area occupied by the wires of the first and second high transmittance conductive meshes ( 183 ,  85 ) is kept as high as possible to provide a high transmittance. 
     Optionally, charged particles, i.e., ions, may be mass selected in the multipole ion guide  186  so that a larger concentration of the charged particles of interest may be delivered into the third chamber  290  through the second opening  187 . Such a feature is advantageous if analysis of charged particles with a large atomic mass is performed in the third chamber  290 . For example, the analysis may be protein analysis by mass spectroscopy. 
     Preferably, the charged particles are extracted from the multipole ion guide  186  by changing the electrical potential on the first and second end cap electrodes ( 182 ,  184 ). In this case, a large diameter is preferred for the multipole ion guide  186  because such a large diameter enables deep penetration of the electrical field generated by the first and second end cap electrodes ( 182 ,  184 ) as described in the first embodiment. In case the vacuum instrumentation  295  comprises a mass spectrometer, well-controlled injection of low-kinetic energy charged particles into the third chamber  290  enables precise control of the trajectory of the charged particles by the electromagnetic field of the mass spectrometer even for charged particles with a high atomic mass. When the trajectories of the charged particles are completely defined by the applied electromagnetic field, accurate high resolution mass measurement may be made for charged particle having a high mass-to-charge ratio. 
     The capture efficiency, or the ratio of the flux of the charged particles through the second opening  187  to the flux of the charged particles through the first opening  139 , is determined by several factors including the velocity distribution of the charged particles, the mass-to-charge ratio of the charged particles, the frequency and voltages of the electrical signal applied to both the multipole ion guide  186  and to the first and second end cap electrodes ( 182 ,  184 ), buffer gas pressure, the opening area and the angle of the conical jet nozzle  212 , and the pressure of the second chamber  180 . The pressure inside the second chamber  180  may be adjusted by adding additional gas to the second chamber  180  and/or throttling the second chamber vacuum pump  176  to optimize the ion capture efficiency. The combination of the control of the directionality and the average velocity of the charged particles from the first chamber  130  into the second chamber  180 , the gas pressure in the second chamber  180 , and the radius of the multipole ion guide  186  are key elements in achieving efficient capture of a large quantity of charged particles, i.e., ions, of any size. 
     Hybrid embodiments employing various elements of the first exemplary particle inlet system and the second exemplary particle inlet system are mixed are contemplated herein also. For example, the first chamber  30  of the first exemplary particle inlet system may replace the aerodynamic lens system implemented as the first chamber  130  in the second exemplary particle inlet system. Also, the set of the second chamber  60  and the third chamber  80  and the peripheral elements attached thereto in the first exemplary particle inlet system may replace the second chamber  180  and the peripheral elements attached thereto in the second exemplary particle inlet system. Further, embodiments in which various axes are tilted relative to another axis are contemplated herein also. Such axes include the axes connecting the various openings for the flow of particles in the exemplary particle inlet systems. 
     While the invention has been described in terms of specific embodiments, it is evident in view of the foregoing description that numerous alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the invention is intended to encompass all such alternatives, modifications and variations which fall within the scope and spirit of the invention and the following claims.