JPS62264546A - Mass spectrograph - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates generally to tandem quadrupole mass spectrometers, and more particularly to low noise tandem quadrupole mass spectrometers.

Conventional technology Tandem quadrupole mass spectrometers are known.

Such mass spectrometers are used to study ion-molecule reactions. A central RF-only four pole has been added to the tandem quadrupole mass spectrometer for photodissociation studies and metastable ion studies.

U.S. Patent Nos. 4,234,791 and 4°329.5
No. 82 discloses a tandem quadrupole mass spectrometer with a high efficiency intermediate splitting stage using collision-induced dissociation (CID) in the form of an RF-only quadrupole.

All known tandem quadrupole mass spectrometers are noisy. This noise is believed to be due to excited fast neutral particles and fast ions moving directly into the region of the detector and hitting surfaces near the detector, generating secondary ions. These secondary ions generate interfering ion currents.

This is detected by a detector.

And five haircuts! SUMMARY OF THE INVENTION The general object of the present invention is to provide an improved tandem quadrupole mass spectrometer.

Another object of the present invention is to provide a tandem quadrupole mass spectrometer that has less noise due to neutral particles and fast ions.

Yet another object of the present invention is to provide a tandem quadrupole mass spectrometer with a curved RF-only intermediate quadrupole stage.

These and other objects of the invention include: an ion source, a lens for guiding ions from said ion source along a predetermined path, and at least one quadrupole filter or analyzer for filtering or analyzing said ions; This is achieved by a mass spectrometer comprising detection means for detecting said ions and quadrupole means for guiding the ions away from said predetermined path so that they impinge on said detection means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

A known tandem quadrupole mass spectrometer is shown in FIG. This mass spectrometer includes a chamber 12, an electron source 1
3 and a collector 14.
1. This ion source 11 is an electronic WI! ! 1
(EI) mode or chemical ionization (CI) mode. Other types of ion sources used in mass spectrometry and suitable for use in the present invention include those that generate secondary ions from a sample liquid matrix or solid sample by bombardment with a beam of fast atoms or ions. It is. These ion sources are used to analyze high mass organic compounds. There are other ionization techniques for use in elemental or inorganic mass spectrometry. These types of ion sources produce more neutral particles and faster ions, resulting in higher noise levels. In either case, the ions generated by the ion source are accelerated and directed by a lens 16 to a quadrupole mass filter or analyzer 17.
directed towards. Neutral particles and fast ions also travel to the quadrupole mass filter.

The quadrupole analyzer or filter 17 operates at a voltage that is periodic from the RF lightning voltage and the DC voltage. Analyzer or filter 17 passes only ions having a selected charge-to-mass ratio. That is, the ions are filtered and only those ions having charge-to-mass ratios within a predetermined range are selected. This range is determined by the RF and DC voltages applied to the quadrupole rod 18. Ions that are not captured by or pass through the quadrupole filter or analyzer hit the walls of the quadrupole rod 18 enclosure and are neutralized. The selected or filtered ions are sent to analyzer 17.

Lens 19 directs ions of selected mass-to-charge ratios passed through analyzer 17 to RF-only actuated rod 2.
It is made to converge to the quadrupole region 21 containing 2. RF-only operation of the quadrupole allows substantially all ions to pass through. Acts as a very broadband bypass filter. - The RF quadrupole region 21 is a separate volume defined by a wall 25 which is also part of the lenses 19 and 24. Collision gas is introduced into the volume through a suitable inlet 23. The ions that have passed through the quadrupole region 21 collide with the gas to form children or fragments of one selected ion. These fragments are.

Passed through lens 24 to a second quadrupole mass filter or analyzer 26 where particles of a selected mass are selected and passed through hole 27 and through an aperture formed in X-ray shield 28 to form negative ions. is sent to dynode 31 or 32 depending on whether positive ions or positive ions are to be analyzed. Secondary ions or electrons generated from the dynode are collected by an electron multiplier 33 and an output signal is generated. A preferred detector is U.S. Pat. No. 4,432.32.
It is disclosed in No. 4. The operation of tandem mass spectrometers including collision-induced dissociation regions is described in U.S. Pat.
No. 234,791 and No. 4,329.582.

As mentioned above, tandem quadrupole mass spectrometers of this type have the disadvantage of being noisy because excited fast neutral particles and fast ions are generated in the ion source. These neutral particles and fast ions travel in a straight line through various quadrupole regions and lenses to the dynode 31.
．． It is thought that it will collide with the surface around 32. Upon hitting these surfaces, positive and negative ions (possibly electrons)
are emitted, these are attracted by the dynode 31 or 32, sensed by the multiplier tube 32, and detected as a signal. This noise is strictly visual! This seems to be a l phenomenon. This is because this does not occur with magnetic sector devices. Such devices have a magnetic field and an electrostatic sector, and thus a curved ion path between the ion source and the detector. In these devices, the detector region is remote from the line of sight of the ion source.

In view of the above discussion, in a triple tandem quadrupole system of the type shown in Figure 1, noise is reduced and neutral particles are detected when the detector assembly is placed away from the ion path of the ion source. It is proposed that the probe move in a straight line towards the detector and avoid hitting surfaces near the detector.

FIG. 2 shows a triple tandem mass spectrometer constructed according to the present invention. Corresponding parts in FIG. 1 are designated with the same reference numerals.

According to the invention, the RF-only quadrupole region is bent, as shown at 36, so that the detector is no longer aligned with the ion source 11. Neutral particles traveling linearly from the ion source 11 therefore strike either the wall of the enclosure or the quadrupole rod 37. Therefore, even if the secondary particles are collected and dispersed, they do not move near the detector.

In summary, the excited neutral particles hit the intervening surface but do not reach the area of the detector and add to the signal. Neutrons are effectively filtered by the RF-only quadrupole region and are not sent to the mass filter. Even if the secondary particles from the excited neutral particles have enough mass to pass through the last quadrupole region 26 to the detector, their initial position is often It is in such a position that it is almost impossible to move forward.

The mass spectrometer of FIG. 2 operates in the same manner as is known, since the curved quadrupole region acts like a straight region for the ions of interest.

Curved quadrupolar regions are known to bend the ion beam. Peter H. Dawson
"Quadrupole Mass Spectrometer and its Applications" edited by Mr. Il, Dawson)
ctrometryand its Applicat
ions) J describes criteria for the operation of curved quadrupole ion beam guides. Generally, the radius of curvature of the axis of the quadrupolar structure must be significantly larger than the characteristic dimensions of the quadrupolar electrode structure.

The theory of operation of quadrupole regions and their ion transport properties are known and disclosed in US Pat. No. 2,939,952. This is also described in detail in the first chapter of the above-mentioned document entitled "Quadrupole mass spectrometer and its applications". In summary, the mode of operating the quadrupole region is RF
There are two types: chisel and RF/DC. When an RF-only voltage is applied between a pair of rods, the device theoretically transmits only ions above a certain threshold or cutoff mass. When a combined RF and DC voltage is applied between the pole pair, both an upper cutoff mass and a lower cutoff mass are provided. As the DC to RF voltage ratio increases, the ion mass transfer band narrows. Quadrupole mass filter operation occurs when the DC to RF ratio is such that the passband of the device is narrow enough to transmit only a single ion mass. The specific range of ion masses passing through the quadrupole region is theoretically determined by the characteristic dimension rO1 of the device.
It is based solely on the magnitude of the applied RF and DC voltages and the frequency of the applied RF. However, since practical devices have length limitations, ion transport is also based on the speed at which the ions travel downstream along the length of the quadrupole region. If ions enter the device at such an axial velocity that they do not undergo a sufficient number of field cycles during their passage through the quadrupole region, only some ions with masses outside the ion mass passband will be transmitted. Generally, as the axial ion velocity increases, the passband range of ion masses becomes progressively broader and less distinct. If the axial velocity is very high, ion transport becomes virtually independent of ion mass.

In the case of a curved quadrupole region, as in FIG. 2, the effect of axial velocity on ion transport is substantially different from that of a straight quadrupole region. At low axial velocities, the strong focusing properties of the quadrupole field are sufficient to diverge all ions into the passband along the curved axis of the quadrupole region.

However, at high axial velocities, ions with masses near the limits of the passband will not undergo a strong enough focus to follow a curved ion path and will not be transmitted. Generally, in the case of a curved quadrupole region, the limits of the ion mass passband become progressively narrower and less defined as the axial ion velocity increases. Naturally, the larger the radius of curvature of the device, the slower this velocity discrimination will begin. A gently curved structure similar to the RF-only quadrupole configuration in Figure 2 is used for conventional frequencies.

When operating in the RF lightning voltage and ion axial velocity ranges, it operates substantially as in the linear configuration. However, the curvature is sufficient to avoid transmitting very fast ions, which are often part of the noise problem.

The invention can also be applied to mass spectrometers that include a single mass filter or analyzer, such as the mass spectrometer shown in FIG. 3, where like parts are designated by the same reference numerals. ing. In this mass spectrometer, the first tandem analyzer or filter stage of FIG. 2 has been eliminated.

The curved quadrupole region 36 can act as both a neutral noise filter and an ion prefilter for the mass spectrometer. A suitable RF/DC voltage is applied to the curved quadrupole region to ensure that only a broad band of ions, about the ion mass being analyzed by the mass filter, reaches the mass filter 26.

This is a particularly suitable mode of operation when the ion source generates an ion beam of mostly one or more than a few ion masses. Apart from neutral noise, interference noise currents are generated in the detector that are related to the magnitude of the total ion current entering the mass spectrometer. Removing the dominant ion mass from the ion beam in the curved quadrupole region before entering the quadrupole mass analyzer correspondingly reduces the noise associated with this ion current and, in turn, removes the important but weaker component ion masses. Detection and measurement will be facilitated.

The curved quadrupole region can be used in other tandem mass spectrometers, such as those used to study photodissociation and metastable ionic structures.

One such tandem mass spectrometer to which the present invention can be applied is a hybrid sector quadrupole device. A simple hybrid sector quadrupole device of the known BEQQ form is shown in FIG. 4. Essentially, this device performs a similar function to the tandem quadrupole device of FIG. Only the mass analyzer of the convergence sector is replaced by the first quadrupole mass filter 17. Parts corresponding to FIG. 1 are designated with the same reference numerals. High resolution analyzer 7
9 is composed of an entrance slit 71, an α-slit 72, a magnetic sector 73, a β-slit 78, an electrostatic sector 74, and an exit slit 75.

The ions generated by the ion source 11 are mass analyzed with high resolution and a 1M ion beam is caused to exit from the exit slit 75. In this regard, low energy CID
Two experiments can be performed: high-energy CID and high-energy CID. The low energy CID experiments are the same as those performed with the apparatus of FIG. The parent ion beam is decelerated by a deceleration lens system 17 and sent to a conventional RF quadrupole collision cell 21 where it is subjected to low energy CID with a kinetic energy of 2 to 200 eV. The child ions are mass analyzed with an RF/DC quadrupole mass spectrometer and detected with a detector. This experiment is very quiet because noisy particles generated in the ion source are not passed through the sector analyzer as described above.

Other experiments, high-energy CID, are not silent. In this experiment, the parent ion beam undergoes CID in a needle collision cell 76 with a kinetic energy of several thousand volts before entering the deceleration lens.

The collision cell consists of a capillary tube 80 that injects a collision gas into the parent ion beam. The child ions generated in this region are decelerated by a deceleration lens, sent through an RF-only quadrupole region to a quadrupole region for mass spectrometry, and detected. The high-energy collision process generates a pair of particle entities, which causes significant noise in the detector. Neutral molecular products are generated with high kinetic or internal energy. These neutral particles are delivered directly to the area of the detector in line-of-sight form, creating noise-generating secondary particles. The child ions also have well-defined and widely distributed kinetic energies. The kinetic energy of a parent ion is distributed over its ionic and neutral progeny in proportion to their mass.

A low mass child ion has a kinetic energy that is hundreds or thousands of electron volts lower than a high mass child of the same parent. Therefore, when a low-mass child ion is slowed down to a speed suitable for mass analysis in a quadrupole mass filter, the other high-mass child ions present still have very high kinetic energy, effectively reducing the mass It passes through the four poles at such high speed that it is not analyzed. These fast child ions can generate very large interfering noise currents in the detector.

This noise can be accounted for by adding kinetic energy analysis means before the quadrupole mass analyzer, but this increases complexity and often reduces the sensitivity of the instrument. Replacing a straight quadrupole region with a curved quadrupole region in a low-energy collision cell is a simple means of removing neutral and fast particle ions generated during high-energy CID. FIG. 5 shows a BEQQ geometric hybrid K ffi in which curved quadrupolar regions are arranged as low-energy collision cells. Figures 2 and 4
Parts corresponding to the figures are designated by the same reference numeral.

In high-energy CID mode, the RF lightning voltage is
A combined voltage of C is applied to the curved quadrupole region to efficiently generate child ions of a specific mass that are analyzed by the quadrupole mass analyzer, while preventing the delivery of high-velocity, high-mass quantum ions. Emphasizes the velocity filter characteristics of the region. Also, the excited fast neutral particles emitted from the high-energy collision cell are not deflected towards the mass analyzer and detector by the curved quadrupole region.

removed from the beam. In low energy CID mode, the curved quadrupole region is RF-only activated and acts similarly to a straight RF-only collision cell, as described above.

In RF/DC mode or RF only mode, the curved quadrupole region reduces the number of neutral particles or fast ions reaching the detection region of the mass spectrometer.

In turn, neutral noise caused by secondary ions generated near the detector is reduced.

Although a curved quadrupole RF-only stage is preferred, a straight quadrupole stage 41 positioned at an angle minimizes the movement of neutral particles and fast ions from the ion source to the detector.

FIG. 6 shows mass spectrometers similar to FIG. 2 with the same reference numbers. However, the RF quadrupole stage has a quadrupole region 17
A straight rod 4 held at an angle with respect to the rod of
1.

Mass spectrometers can exhibit high noise immunity using one or more curved or angled sections. Figure 7 shows a system with three RF sections 46, 47 and 48, two of which are curved and one straight. The central straight section 47 has a gas inlet 49 and operates in CID mode. The RF-only quadrupolar region is
It consists of a combination of straight parts and curved parts. The mass spectrometer shown in FIG. 8 comprises an RF section in which outer straight sections 52 and 53 are separated from a CID section 54 which includes a curved rod section 56 and a straight section 57.

It is clear that many combinations of quadrupole filters or analyzers, RF-only sections, CID or other sections are possible. All that is true is that the detector is offset from the ion source and neutral particles or fast ions cannot be directly delivered or transported.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a tandem quadrupole mass spectrometer according to the known technology, FIG. 2 is a schematic diagram showing a low noise tandem quadrupole mass spectrometer according to the present invention, and FIG. 3 is a schematic diagram showing a tandem quadrupole mass spectrometer according to the present invention. Schematic diagram showing another example. FIG. 4 is a schematic diagram showing a tandem sector quadrupole mass spectrometer according to the known technology; FIG. 5 is a schematic diagram showing a tandem sector quadrupole mass spectrometer according to the present invention; FIG. FIG. 7 is a schematic diagram showing a further embodiment of the present invention, and FIG. 8 is a schematic diagram depicting a further embodiment of the present invention. It is a diagram. 11...Ion source 12...Chamber 13...Electronic saw 14...
- Collector 16... Lens 17... Mass filter or analyzer 18... Quadrupole rod 19... Lens 21... Quadrupole region 22... Rod 26...
- Filter or analyzer 27...hole 28...X-ray shield 31.
32... Dynode 33... Electron multiplier tube 36... Quadrupole region 37... Quadrupole Rondo procedure correction writing method) 62.6. -4 Director of the Japan Patent Office Black 1) Mr. Akihiro 1. Indication of the case 1988 Patent Application No. 51825 2. Title of the invention Mass analyzer 3. Person making the amendment Relationship with the case Applicant Name Finnigan Corporation 4, Agent 5, Date of amendment order May 26, 1985 Procedural amendment Commissioner of the Patent Office Black 1) Akio Yu 1, Indication of case 1988 Patent Application No. 51825 2, Title of the invention Mass analyzer 3, Relationship with the person making the amendment Applicant's name: Finnigan Corporation 4, Figures 3, 5, 6, and 7 of the agent's drawings are corrected as shown in the attached sheet. Roll! ,・ゝ′

Claims (8)

[Claims] (1) an ion source; means for guiding ions from the ion source along a predetermined path; and an ion filter or analyzer for receiving the ions and producing output ions within a selected mass-to-mass ratio range. a quadrupole means for receiving the output of said ion filter or analyzer and guiding ions away from said predetermined path; and a quadrupole ion filter or analyzer for receiving the output of said quadrupole means; A mass spectrometer, characterized in that it comprises a quadrupole ion filter or a detection means arranged to receive the output of the analyzer. 2. A mass spectrometer according to claim 1, further comprising means for supplying RF and DC signals to the quadrupole means. (3) The mass spectrometer according to claim 2, wherein the quadrupole means includes a bent quadrupole rod. 4. A mass spectrometer according to claim 3, wherein said quadrupole means comprises a straight rod angled relative to said path. (5) The mass spectrometer according to claim 2, wherein the quadrupole means includes a straight rod and a bent rod. (6) The mass spectrometer according to claim 2, further comprising means for introducing collision gas into the quadrupole means. (7) means for guiding ions to be analyzed or filtered along a predetermined path; quadrupole means for guiding said ions away from said predetermined path; and receiving said ions and analyzing or filtering said ions. A hybrid tandem mass spectrometer comprising: a quadrupole ion filter or analyzer; and detection means offset from the path and arranged to receive the output from the quadrupole ion filter or analyzer. (8) The mass spectrometer according to claim 7, wherein the quadrupole means includes a bent quadrupole rod.