EP0023826B1 - Tandem quadrupole mass spectrometer system - Google Patents
Tandem quadrupole mass spectrometer system Download PDFInfo
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- EP0023826B1 EP0023826B1 EP19800302635 EP80302635A EP0023826B1 EP 0023826 B1 EP0023826 B1 EP 0023826B1 EP 19800302635 EP19800302635 EP 19800302635 EP 80302635 A EP80302635 A EP 80302635A EP 0023826 B1 EP0023826 B1 EP 0023826B1
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- European Patent Office
- Prior art keywords
- rods
- sets
- quadrupole
- voltages
- ions
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J49/00—Particle spectrometers or separator tubes
- H01J49/26—Mass spectrometers or separator tubes
- H01J49/34—Dynamic spectrometers
- H01J49/42—Stability-of-path spectrometers, e.g. monopole, quadrupole, multipole, farvitrons
- H01J49/4205—Device types
- H01J49/421—Mass filters, i.e. deviating unwanted ions without trapping
- H01J49/4215—Quadrupole mass filters
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J49/00—Particle spectrometers or separator tubes
- H01J49/004—Combinations of spectrometers, tandem spectrometers, e.g. MS/MS, MSn
Description
- This invention relates to a tandem quadrupole mass spectrometer system.
- In a paper published at page 2274 of the 1978 issue of Journal of the American Chemical Society R. A. Yost and C. G. Enke have published a letter disclosing that a tandem mass spectrometer system may be used to create ion species from a sample, select one individual ion species, fragment that species, and obtain the mass spectrum of the fragments. The letter discloses that a quadrupole mass filter, an AC-only quadrupole section, and a second quadrupole mass filter are arranged in series. Gas is introduced into the center quadrupole section to produce collision induced dissociation. Each quadrupole is arranged in its own cylindrical container with end apertures and operates separately. With a system such as this,. it is found that ion signal losses are very large as the ions travel from one quadrupole to the next, and therefore the sensitivity of the apparatus is greatly reduced.
- There is a problem therefore to reduce losses of ions between one quadrupole and the next in such a system, to improve sensitivity.
- The present invention as claimed is intended to provide a remedy.
- With the present invention it is found that greatly increased ion transmission can be achieved in most instances by close coupling the quadrupole sections together and by providing a specific relationship for the AC fields in the tandem sections.
- Embodiments of the invention will now be described, by way of example with reference to the accompanying drawings in which:
- Fig. 1 is a partly diagrammatic cross-sectional view of a mass spectrometer system which may be used with the present invention;
- Fig. 2 is a cross-sectional view of the apparatus of Fig. 1 taken along lines 2-2 of Fig. 1;
- Fig. 3 is a perspective view, partly in section, showing the rods of one of the mass spectrometers of Fig. 1 mounted in a holder;
- Fig. 4 is an end view showing open structure rods of the mass spectrometer system of Fig. 1;
- Fig. 5 is a side view showing the rods of Fig. 4;
- Fig. 6 is a standard stability diagram for a mass spectrometer;
- Fig. 7 is a plot showing diagrammatically the rise and fall of the AC field along the length of the tandem mass spectrometer system of Fig. 1;
- Fig. 8 is a plot showing typical emittance or acceptance elipses for a mass spectrometer;
- Fig. 8a is an end view of the rods of a mass spectrometer showing the x and y directions;
- Fig. 9 is a plot showing typical emittance and acceptance elipses for the system of Fig. 1 in the y direction;
- Fig. 10 is a plot showing typical emittance and acceptance elipses for the system of Fig. 1 in the x direction;
- Fig. 11 is a plot showing the travel time of an ion through the system of Fig. 1 expressed in terms of cycles of the applied AC field;
- Fig. 12 is a plot showing the characteristics of a typical ion source;
- Figs. 13 to 29 are plots showing envelope functions for various mass spectrometer systems of the kind shown in Fig. 1; and
- Fig. 30 is a block diagram of an electrical control system for use with the mass spectrometer system of Fig. 1.
- Reference is first made to Fig. 1, which shows a specific mechanical arrangement which may be used to implement the invention.
- Fig. 1 shows a vacuum chamber generally indicated at 2 and which contains three mass specttometer sections generally indicated at 4, 6, and 8 respectively. Spectrometer section is of conventional quadrupole square pattern.
Spectrometer section 8 is also a conventional quadrupole mass spectrometer and similarly contains fourrods 12 arranged in a normal square pattern.Spectrometer section 6 also contains fourrods 14, arranged as shown in Fig. 3 in normal quadrupole fashion. However therods 14 have solid center portions, indicated at 14-1, and open structure and extensions, indicated at 14-2. - The center portions 14-1 of
rods 14, and also therods quadrupole sections plates 16 ofquadrupole sections housings 18 haveapertures 20 therein to allow gas within themass spectrometer sections rods 14 are however housed in acylindrical can 22 which is closed except at its ends, which are defined byend discs 24 havingapertures 26 therein. In addition aduct 28 carries a target gas from asource 29 into thecan 22 and into the space between the centre portions 14-1 ofrods 14. - The open structure rod extensions 14-2 of the
rods 14 are formed, as shown in Figs. 4, 5 of thin stiff rods orwires 30. Each set ofwires 30 is arranged in a curved configuration to simulate the shape of the outer portion of a normal quadrupole rod, so that the field produced by the four sets ofwires 30 will correspond as closely as possible to the normal hyperbolic field 31 (Fig. 4) produced by the solid rods of a conventional quadrupole. Thewires 30 are supported at their inner ends by welds or solder connections to the solid rod portions 14-1. At their outer ends thewires 30 are supported by a holder 32 (see especially Fig. 5) which also acts as a barrier to help limit the amount of gas from thecentre quadrupole section 6 entering theend quadrupole sections central aperture 32a to permit ions to pass therethrough. Typically five thin wires may be used, spaced around somewhat less than half the inner circumference of the equivalent solid rod. - The three
quadrupole sections cylindrical vacuum chamber 2, being held in position by support members not shown. Each rod of each of the three sets is aligned axially with each corresponding rod of each other set, so that the spaces between the rods of each set are linearly aligned, for ions to pass therethrough. The ends of therods - The end wall of the
vacuum chamber 2 contains anaperture 34 through which ions to be examined are supplied from anion source 36.Ion source 36 may typically be the source shown in U.S. patent 4,148,196, in which a trace gas is admitted to an ionization chamber, ionized, and the resultant ions are drawn by appropriate electric potentials through a curtain gas chamber into thevacuum chamber 2. Curtain gas in the curtain gas chamber serves to block entry of unwanted materials into thevacuum chamber 2, and the curtain gas, which may typically be pure nitrogen, also enters the vacuum chamber where it is cryopumped thus permitting maintenance of a high vacuum in thevacuum chamber 2. - As shown in Figs. 1 and 2, appropriate cooling means are provided to cryopump the curtain gas entering the
vacuum chamber 2. Specifically, a refrigeratingmechanism 38 is provided having an inner tubular finger or firstcold station 40 and an outer finger or secondcold station 42. Themechanism 38 is typically able to extract 2-4 watts of thermal energy from theinner finger 40 at 20°K, and is also typically able to extract 5-10 watts of thermal energy from theouter finger 42, at 70 to 90°K. - A copper support tube 44 is mounted on top of the
inner finger 40, in good thermal contact therewith, and supports at each end acylindrical shell 46, also made of good thermal conducting material such as copper. Theshells 46 have end walls 48 and contain slots (not shown) in their upper surfaces so that thecenter quadrupole section 6 may be fitted downwardly into theshells 46. - A pair of
intermediate shells 52 are connected to theouter finger 42 and serve to reduce the heat load on theinner shells 46. Theintermediate shells 52 are mounted on an outercopper support tube 54 concentric with the inner support tube 44, theouter tube 54 being mounted on thesecond finger 42. The exterior surfaces of theintermediate shells 52 are insulated with aluminized plastic film, as indicated at 56, to reduce heat radiation to theintermediate shells 52. The outer end walls of theintermediate shells 52 containinset centre sections 60 spaced byannular gaps 62 from the outerend wall sections 64 and supported thereon by support struts, not shown. Thegaps 62 assist in cryopumping gas from theend quadrupole sections intermediate shells 52 also contain slots, shown at 66, Fig. 2, in their upper surfaces to facilitate assembly of the operations. - In operation, ion species from a sample to be considered are supplied from
ion source 36 and are focused (by conventional means not shown) to enter thefirst quadrupole section 4. In the first quadrupole section ions of the desired mass are selected and enter thecentral quadrupole section 6. In thecentral quadrupole section 6, the ions encounter a target gas supplied viaduct 28 into thespace 68 between therods 14 of the center quadrupole section. The resultant collisions induce dissociation of the ions into fragments or daughter ions, which are then transmitted into thethird quadrupole section 8. Thethird quadrupole section 8 acts as a mass filter, selecting the desired fragments or daughter ions for detection by anion detector 70. In order to act as mass filters, theend quadrupole sections center quadrupole section 6, which must pass a wide range of masses, has only an AC voltage applied to itsrods 14. The gas pressure in the first andthird quadrupole sections vacuum chamber 2 is pumped either by being fitted with appropriate cryo-cooling surfaces, as explained in patent 4,148,196, or by vacuum pumps connected toports 72 in thechamber 2. Target gas in thecenter quadrupole section 6, which tends to enter the space between the rods of theend quadrupole sections wires 30 and condensing on the cooled surfaces ofinner shells 46. - The advantages of the open structure of the rod extensions 14-2, formed by
wires 30, are as follows. Normally in a quadrupole section the gap d1 (Fig. 3) between the rods is relatively small compared with the diameter d2 of the rods (typically d1 may be about one third of d2). Thus if the rods are solid, relatively little gas can escape between them, and therefore a substantial gap must be left between the ends of adjacent quadrupole sections, so that the gas can exit through this gap and so it will not unduly pressurize the cans of theend quadrupole sections - With the open structure rod extensions 14-2 shown, the
quadrupole sections small gap 33 as discussed. Since a quadrupole section having an AC-only field applied thereto requires less accuracy of manufacture than a quadrupole section having both AC and DC applied to its rods, the open structure described may be used with little or no degradation in performance. Provided that the open sections 14-2 are of reasonably substantial length, only a small proportion of the target gas entering thecentre quadrupole section 6 will travel into theend sections - In a typical system of the kind described, the parameters of the system may be adjusted so that the gas density in the target region, i.e. in the space between rods 14-1, is in the range between 1.3 Pa and 1.3 x 1 0-2 Pa (10-2 torr and 10-4 torr) and the lengths of rod extensions 14-2 are each equal to the lengths of rods 14-1 (e.g. 4 inches). Then most of the gas in the
target region 68 travels outwardly through the gaps between thewires 30, as indicated byarrows 76, Fig. 5. Only a small proportion of the gas, indicated byarrows 78, is beamed directly into the space between the rods of theend quadrupole sections end quadrupole sections duct 28. - Although the rods of the
centre quadrupole section 6 are shown as having solid centre sections, they can be entirely of open construction, formed by thin wires stretched in tension between end discs spaced apart by support bars. - Alternatively, the rods of the centre section can be constituted by groups of longitudinally extending wires, using the principles given in a paper published by H. Matsuda and T. Matsuo entitled "A New Method of Producing an Electric Quadrupole Field", published in the International Journal of Mass Spectrometry and In Physics, No. 24, 1977 at page 107. By using such principles a quadrupole field can be produced using a number of wires suitably located, and not necessarily in the same locations as the usual solid rods themselves would assume. Such structure can be used and a gas target region created within it, provided that there is minimal interference with gas escaping from the structure. The groups of wires which produce a quadrupole field in effect act as rods and the term "rods" in the appended claims refers to any groups of wires or other structure which produces a quadrupole type field.
- Where it is desired to study for example the metastable decomposition of ions, then there is no need to introduce gas into the
centre quadrupole section 6 and the rods then need not be of open structure. - It is found that close coupling the mass spectrometer sections, permitted for example by the structure shown in Figs. 1 to 5, has substantial advantages relating to the transmission of ions through the tandem sections. Reference is made to Fig. 6, which is a standard stability diagram for a quadrupole mass spectrometer. Fig. 6 plots "a" against "q", where
- m is the mass of the ion passing through the spectrometer,
- r is the radius of the inscribed circle between rods,
- w is the angular frequency of the applied AC,
- e is the electronic charge.
- As shown, a quadrupole mass spectrometer has a high mass cutoff, indicated by
line 100, and a low mass cutoff, indicated byline 102. The shadedarea 104 between the high mass and lowmass cutoff lines mass cutoff lines - The equations given are for infinitely long. rods, and where the rods end, the fields fall off. Although the equations do not apply exactly beyond the ends of the rods, it is found that effectively the AC and DC voltages fall off together outside the rods so that an ion approaching the rods may for example find itself at
point 106 as it approaches the rods and then atpoint 108 as it travels within the rods.Point 106 is outside the stable region and hence many ions are usually lost where an ion stream enters or leaves a quadrupole field. - Reference is next made to Fig. 7, which shows diagrammatically the three.
quadrupole sections field amplitude 110 does not fall to zero and then rise up again between sections; instead the field amplitude in thetransition regions sections section 6. Typically the value of q in thesections sections centre section 6 will be about .2, so that when ions are fragmented thereby producing daughter ions of smaller mass, q for the daughter ions will not increase to such a high value as to be outside low mass cutoff line 102 (which would cause the daughter ions not to be transmitted). Since in the transition regions the field does not fall to zero, but instead the operating conditions remain within the stability region, less ion signal is lost. - It is also found that the transmission of ions from one quadrupole to another is different for each phase of the applied AC field. Reference is made to Fig. 8, where the value "µ" is plotted against "µ", where µ is the displacement of an ion in either the x or y direction between the rods, divided by ro, and µ is the velocity in the µ direction. Fig. 8 should be considered together with Fig. 8a, which shows the x and y directions and ro for a set of
rods 10. The x direction is the direction between the positively changedrods 10, assuming that positively charged ions are being analyzed, while the y direction is then the direction between the negatively chargedrods 10. (For thecentre section 6, where there is no DC, the x and y directions are the same). It will be appreciated that if µ exceeds 1, then either x or y (depending on which µ represents) exceeds ro, meaning that ions of interest are contacting a rod and are being lost. - As illustrated in Fig. 8, it is known that all ions within the
stable region 104 of the stability diagram of Fig. 6 and which enter between therods 10 at a given initial phase of the AC field, and have values of µ and µ within an elipse such as that indicated at 116, will travel throughrods 10; all other ions will be lost by contact with the rods. As the initial phase changes, theellipse 116 rotates and changes its shape, and a typical ellipse for ions entering at a different phase of the AC field is indicated at 118 in Fig. 8.Ellipses - When a quadrupole is operating near the tip of its stability diagram, i.e. near point 120 (Fig. 6), the resolution of the quadrupole is higher since the region in which ions are stable is smaller, and therefore the acceptance or emittance elipses of a quadrupole operating near the
point 120 become smaller in area. However when a quadrupole is operated with AC only on its rods, it operates on the q axis and the region of stable operation is much larger, so it is a much less selective mass filter. Therefore the acceptance and emittance ellipses of theend quadrupole sections centre quadrupole section 6, where AC only is applied. - It may be noted that the emittance and acceptance ellipses are calculated by following the movement of a typical ion, using the fundamental equations of motion for the ion, and integrating them numerically to determine the path of the ion. A program for calculating the ellipses is contained in a publication entitled "Quadrupole Mass Spectrometry", edited and partly authored by Peter Dawson, and published in 1976 by Elsevier.
- Reference is next made to Fig. 9, which shows emittance ellipses for
end quadrupole section 4 and acceptance ellipses for thecenter quadrupole section 6. The ellipses drawn are for the y direction, i.e. in the plane extending between the negatively biased rods assuming that the ions under analysis are positively biased. The emittance elipses for thequadrupole section 4 are shown in solid lines at 4yO to 4y9 for 10 different initial phases of the AC field. The ten phases are .1 cycles, i.e. 36°, apart. It will be seen that the axis of the initial ellipse 4y0 is rotated slightly clockwise from the horizontal and that the subsequent ellipses rotate and change in shape as they are rotated. The direction of rotation is not uniform and although ellipse 4y2 is rotated counterclockwise from ellipse 4y1, ellipse 4y4 is rotated clockwise from ellipse 4y3. Six of the acceptance ellipses for thecentre quadrupole section 6, for the y direction, are shown in dotted lines in Fig. 9 at 6yO and 6y5 to 6y9. The remaining four phases are symmetrical with phases 6y6 to 6y9 and are therefore not plotted. It is found that the best overall matching of the emittance and acceptance ellipses, for maximum transmission of ions in the y direction, occurs when the frequencies and phases of the AC fields applied to all of therod sections - Although ellipses 4yO to 4y9 have been described as emittance ellipses for
quadrupole section 4, they can, since the system is symmetrical, also be regarded as acceptance ellipses for thequadrupole section 8, and ellipses 6y0 to 6y9 can be regarded as emittance ellipses forcentre quadrupole section 6. Again best matching in the y direction occurs when there is little or no phase shift between the AC voltages applied to the three rod sections, although there will be more losses in ions traveling fromsection 6 tosection 8 since emittance ellipses 6y0 to 6y9 are larger than acceptance ellipses 8y0 to 8y9. - Matching is generally more difficult-in the x direction than in the y direction. Reference is next made to Fig. 10, which shows in solid lines emittance ellipses 4x0 to 4x9 for the
end rod section 4 and shows in dotted lines acceptance ellipses 6x0 and 6x5 to 6x9 for thecenter rod section 6. (The remaining acceptance ellipses for thecentre rod section 6 are symmetrical with ellipses 6x6 to 6x9). Although it is not immediately apparent from Fig. 10, it is again found, by an analysis to be discussed, that best overall ion transmission occurs when there is little or no phase shift between the AC voltages applied to all three rod sections. - To solve the problem of determining the phase relations which will provide the best transmission of ions through the three tandem rod sets, a number of envelope function diagrams have been prepared. Reference is next made to Fig. 11, which explains the interpretation of the envelope function diagrams. In Fig. 11, the envelope E is plotted on the vertical axis and the location of ions as they travel through the three tandem quadrupole spectrometers is plotted on the horizontal axis. The horizontal axis is divided into tenths of AC cycles, marked from 0 to 760 (76 cycles). As the ions from the
ion source 36 approach the first rod set 4, assuming a uniform speed for the ions, they pass through an entrance fringing field indicated at 130 and which typically is two cycles in length. The ions then travel through thefirst rod section 4, this process for example occupying 34 cycles, which are indicated at 132. The ions then pass through a 2cycle fringing field 134 to thesecond rod section 6, where they spend (for example) 15 cycles in thesecond rod section 6. This period is indicated at 136. The ions then pass through another 2 cycle transition region or fringing field 1.38 to thethird rod section 8 where they spend (for example) 19 cycles as indicated at 140. The ions then leave thethird rod section 8, passing through another twocycle fringing field 142, and travel to theion detector 70. - The envelope value E which is plotted along the vertical axis represents the largest displacement of any ion at any time at the location in question, divided by ro. The envelope functions are calculated for the x and y directions by determining the trajectories of representative ions according to the techniques used in linear accelerator design, as explained in a book entitled "High Energy Beam Optics" by Claus G. Steffen, a Wiley Et Sons publication, with reference particularly to
chapter 4 section 5. The envelope functions to be discussed assume (except where indicated) the use of a source characterized as shown in Fig. 12 by an envelope E=0.2 (which indicates how far transversely the source emits ions), a maximum angular deviation A of -0.028 and an area of 0.0025 π. These are typical normal values for an ion source. - The ehvelope functions E shown in Figs. 13 and following are each for ten different initial phases of the AC field, i.e. each envelope function is actually ten different curves superimposed on each other. If the value of E exceeds 1, this indicates that some ions are being lost by contact with the rods. Of course even when E exceeds 1, ions entering at some initial phases will be transmitted although ions entering at other initial phases will be lost.
- Fig. 13 illustrates the preferred case where there is zero phase shift between
sections - Fig. 14 illustrates the Y envelope function where there is a phase shift of +0.1 cycle (36 degrees) between
section 4 andsection 6, but no phase shift betweensections - Fig. 15 illustrates the Y envelope function where there is a phase shift of -.2 cycles (72 degrees) between
sections sections centre section 6 and considerably exceeds 1 in thethird section 8 even though there is no phase shift betweensections sections sections - Fig. 16 illustrates the Y envelope function where there is a phase shift of -0.1 cycles (36 degrees) between
sections 4 and 6 (i.e. a smaller shift than Fig. 15), and again no shift betweensections second sections third section 8, indicating some losses, although not unduly large losses. - Fig. 17 illustrates the Y envelope function where there is a phase shift of +0.2 cycles (72 degrees) between
sections sections sections section 8, indicating slight losses in the Y direction. - Fig. 18 illustrates the Y envelope function where there is no phase shift between
stages stages third stage 8 is reached, where it then exceeds 1, indicating some ion losses. - Fig. 19 illustrates the Y envelope function where there is a phase shift of -0.05 cycle (-18 degrees) between each section, i.e. between
sections sections third section 8, indicating some transmission losses. - In the preceding examples, Figs. 13 to 19, it was assumed that in the first and
third section centre section 6, a=0 and q=0.2. - Fig. 20 illustrates the Y envelope function for an instrument operation at higher resolution (operating point a=0.236098 and g=.706, corresponding to a resolution of about 220), where there is no phase shift between sections. It is assumed that the ions spend 28 cycles in
section 4, 15 cycles insection 6 and 27 cycles insection 8. At this higher resolution E exceeds 1 in the first andthird sections - Fig. 21 shows the Y envelope function for the same situation as in Fig. 20 but with a phase change of 0.1 cycles (36 degrees) between
sections 4 and 6 (no shift betweensections 6 and 8). This reduces transmission considerably, as can be seen from the increased value of E. Detailed calculations show a reduction in transmission by a factor of about three as compared with the Fig. 20 case. - Fig. 22 shows the Y envelope function for the same situation as in Fig. 20 but with a phase change of only 0.03 cycles (11 degrees) between
sections 6 and 8 (no shift betweensections 4 and 6). Here E exceeds 1 in the first andthird sections - Transmission in the x direction is normally less than in the y direction, and the results depend on the particular source and on the ion energy, i.e. the number of cycles in the transition region between each quadrupole section. Figs. 23 to 26 show four different x envelope functions, as follows:
- Here the operating point is assumed to be defined by a=0.23342 and q=0.706; resolution 50. The ions take 2 AC cycles to pass through each fringing field region. The ions spend 28 cycles in the
first section 4, 15 cycles in thesecond section 6, and 27 cycles in thethird section 8. The assumed source of ions has an envelope E=0.1, a maximum angular deviation A=0.0177, and an area=0.00125 7r. There is no phase shift between any ofsections ion detector 70 is about 23%. - The conditions here are the same as for Fig. 23, but there is a phase shift of -0.1 cycles (-36 degrees) between the second and
third sections 6, 8 (and no phase shift between the first andsecond sections 4, 6). This results in a small improvement in transmission in the X direction. - The conditions here are the same as for Fig. 23, but there is a phase shift of +0.1 cycles between the second and
third sections 6, 8 (and again no phase shift betweensections 4, 6). This results in a small decrease in ion transmission in the X direction as compared with Fig. 23. - This is an example at the same resolution as Fig. 23 but with a lower mass or higher energy ion which spends only 0.5 cycles in each transition region. (The ion also spends 30 cycles in the
first section 4, 15 cycles in thecentre section - For some operating conditions it has been found by Peter Dawson that it is advantageous to operate the
third section 8 with DC voltages switched with respect to thefirst section 4, but with synchronization of the AC voltages throughout. Fig. 27 shows an x to y envelope function in which the parameters are the same as for Fig. 2.3 but the DC for thethird section 8 is switched to give an xy combination, and the AC is synchronized in phase for all three sections. It will be noted that considerable improvement in ion transmission occurs as compared with Fig. 23. - Fig. 28 shows an x to y envelope function under the same conditions as for Fig. 27, except that there is a phase shift of -0.1 cycles between the second and
third sections - Fig. 29 shows a y to x envelope function under the same conditions as for Fig. 27 but with the DC for the
third stage 8 switched in the oppositive transverse direction from that of Fig. 27 (still 90 degrees out of phase with Fig. 23). The AC is synchronized in phase for all three sections. This results in a considerable improvement in transmission. - In summary, it will be seen that it is important to have close spacing between the coupled quadrupoles in order to achieve high ion acceptance and transmission. The spacing should not normally exceed ro, the radius of the inscribed circle between the rods. If ro varies for the three sections, the spacing will normally not exceed the smallest r o. It will also be seen that the degree of phase shift in the y direction is important and becomes more important at high resolution. For best transmission in the y direction the phase shift should be below 0.1 cycles and preferably below 0.03 cycles, and typically will be zero or nearly zero.
- The degree of importance of phase synchronization in the x direction depends on the operating conditions, and while a phase shift of 0.1 cycles is not always deleterious, full in- phase synchronization usually gives near optimum performance.
- An electrical circuit for controlling phase relations between the quadrupole sections is shown in block diagram form in Fig. 30. As drawn, an
oscillator 180 is provided which produces an AC voltage of the frequency required for mass spectrometer operation (typically 2 to 3 MHz). The AC voltage is applied through a buffer amplifier 182 (which prevents feedback) to apower amplifier 184 and to theAC terminals 186 of thefirst quadrupole section 4. DC is supplied by rectifying a portion of the power amplifier output in arectifier 188 and applying the resultant DC to theterminals 186. Mass selection is controlled by amass command unit 190, which by varying the output ofbuffer amplifier 182 controls the level of the AC (and hence also the DC) voltage applied toterminals 186. This changes the operating point of thefirst quadrupole section 4, in order to select a desired mass for transmission through therods 10. - The
oscillator 180 is also connected through aphase shifter 194 to anotherbuffer amplifier 194. The output ofamplifier 192 is connected to anotherpower amplifier 196 which applies AC to theterminals 198 ofrods 14 of thecentre quadrupole section 6. No DC is applied to therods 14. This arrangement ensures that the AC voltage applied torods 14 is synchronized in frequency and phase with that applied torods 10 so that the resultant AC fields are synchronized in frequency and phase. As discussed, the phase shift is preferably zero or nearly zero. - The
oscillator 180 is also connected through a second phase shifter -200 to anotherbuffer amplifier 202. The output ofbuffer amplifier 202 is connected topower amplifier 204 which is connected to theAC terminals 206 of therods 12 of thethird quadrupole section 8. DC is again supplied by arectifier 208, and the level of the voltages applied is controlled by amass command unit 210 which adjusts the output ofbufter amplifier 202. The use ofphase shifter 200 again ensures that the AC voltage applied to therods 12 is synchronized in frequency and phase with the AC voltage applied to therods - The DC voltages applied to the
rods - Although the invention has been described for use with three quadrupole sections in series, it may also be used with only two such sections in series, namely an AC-only section and an AC-DC section. In such system ions entering a vacuum chamber are guided into a conventional AC-DC quadrupole mass spectrometer by an AC-only section arranged in series with the conventional section, the rods of the AC-only section being of open construction to permit gas entering with the ions to flow through the rods and escape. The same phase and spacing relationships described previously apply.
Claims (17)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA000333327A CA1134957A (en) | 1979-08-03 | 1979-08-03 | Tandem mass spectrometer with synchronized rf fields |
CA333327 | 1979-08-03 |
Publications (2)
Publication Number | Publication Date |
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EP0023826A1 EP0023826A1 (en) | 1981-02-11 |
EP0023826B1 true EP0023826B1 (en) | 1984-03-07 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP19800302635 Expired EP0023826B1 (en) | 1979-08-03 | 1980-08-01 | Tandem quadrupole mass spectrometer system |
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EP (1) | EP0023826B1 (en) |
CA (1) | CA1134957A (en) |
DE (1) | DE3066835D1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
USRE40632E1 (en) | 1999-12-03 | 2009-02-03 | Thermo Finnigan Llc. | Mass spectrometer system including a double ion guide interface and method of operation |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB8305228D0 (en) * | 1983-02-25 | 1983-03-30 | Vg Instr Ltd | Operating quadrupole mass spectrometers |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2283547A2 (en) * | 1974-08-30 | 1976-03-26 | Extranuclear Lab Inc | Spatial separation of AC and DC fields in quadrupole mass filter - using material acting as dielectric to AC and conductor to DC fields |
DE2539161C2 (en) * | 1975-09-03 | 1981-12-24 | Varian Mat Gmbh, 2800 Bremen | mass spectrometry |
US4148196A (en) * | 1977-04-25 | 1979-04-10 | Sciex Inc. | Multiple stage cryogenic pump and method of pumping |
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1979
- 1979-08-03 CA CA000333327A patent/CA1134957A/en not_active Expired
-
1980
- 1980-08-01 EP EP19800302635 patent/EP0023826B1/en not_active Expired
- 1980-08-01 DE DE8080302635T patent/DE3066835D1/en not_active Expired
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
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USRE40632E1 (en) | 1999-12-03 | 2009-02-03 | Thermo Finnigan Llc. | Mass spectrometer system including a double ion guide interface and method of operation |
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CA1134957A (en) | 1982-11-02 |
DE3066835D1 (en) | 1984-04-12 |
EP0023826A1 (en) | 1981-02-11 |
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