Method for tandem mass spectrometry analysis in ion trap mass analyzer

Abstract

This invention is related to a tandem mass spectrometric analysis method in ion trap mass analyzer. Such method comprise three stages as represented by selective isolation, collision induced disassociation and mass scanning of ion. At the collision induced isolation stage, this invention is expected to endow parent ion of certain mass-charge ratio with energy through resonance excitation by changing cycle of radio frequency signals, namely frequency of radio frequency voltage imposed on the ion trap; such high-energy ions produced through resonance excitation are to be disassociated through collision with neutral molecules in the ion trap, which will further generate product ion to realize tandem mass spectrometric analysis. Advantage of this method lies in the fact that it can realize collision induced disassociation by changing scanning cycle at the stage of collision induced disassociation stage through software configuration, which can significantly simplify experimental devices and methods for tandem mass spectrometric analysis.

Claims

1. A tandem mass spectrometric analysis method in an ion trap mass analyzer, comprising three stages as represented by selective isolation, collision induced disassociation and mass scanning of ion in proper sequence, wherein: selected parent ion is to be isolated at said stage of selective isolation of ion; whereas parent ion isolated is to be confined in the ion trap through collision with neutral gas molecules and cooling under the action of electric field produced by working voltage in ion trap; at said collision induced disassociation stage, cycle of ion excited radio frequency voltage signals imposed on the ion trap pole is changed, to further change cycle of radio frequency voltage produced by resonance excitation of ion; as a result of it, ion of certain mass-charge ratio is to be provided with higher energy, subjecting to resonance excitation by ion excited radio frequency voltage of certain cycle or frequency; ion subjecting to resonance excitation is to be disassociated to generate fragment ion through collision with neutral molecules in ion trap; fragment ion subjecting to cooling in ion trap is to be confined for follow-up mass analysis; at said mass scanning and analysis stage, ion in ion trap is to subject to resonance excitation under the action of dipolar excitation voltage as imposed on the electrode of ion trap: eventually, it is to be discharged from lead-out bole or groove of ion extraction electrode to capture mass spectrometry signals, subjecting to detection on ion detector outside ion trap, wherein voltage amplitude and duty ratio of digital bound radio voltage remain unchanged at said stage of collision induced disassociation; cycle of digital radio voltage is to be selected while its initial and final cycle value remain unchanged; further select a certain frequency division number n, namely frequency relation between cycle of ion excited radio voltage and digital bound radio voltage (n=/2); in view of relation with value , cycle of ion resonance excited radio voltage is to be changed while duty ratio remains unchanged; accompanied by variation to ion resonance excited radio voltage, collision energy is to be produced through resonance motion among ions.

2. The tandem mass spectrometric analysis method according to claim 1, wherein mass-to-charge ratio is to subject to linear scanning at said mass scanning and analysis stage.

3. The tandem mass spectrometric analysis method according to claim 1, wherein wave form of ion excited radio voltage signals imposed is digital square wave or sine wave at said stage of collision induced disassociation.

4. The tandem mass spectrometric analysis method according to claim 1, wherein neutral cooling gas delivered to ion trap is to be supplemented at the said stage of collision induced disassociation.

5. The tandem mass spectrometric analysis method according to claim 1, wherein frequency and amplitude of digital bound radio voltage are in constant value at said stage of collision induced disassociation.

6. The said tandem mass spectrometric analysis method according to claim 1, wherein the frequency ratio between ion excited radio voltage and digital bound radio voltage is random at the said stage of collision, induced disassociation.

7. The tandem mass spectrometric analysis method according to claim 1, wherein said ion trap is a 3D or 2D linear ion trap.

8. The tandem mass spectrometric analysis method according to claim 1, wherein said ion trap is ion trap array or field regulated ion trap.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is the wave form diagram for square wave and sine wave driving ion trap; wherein, (a) and (b) are wave form diagrams for symmetrical square wave and sine wave respectively.

(2) FIG. 2 is the structural diagram for experimental platform of instrument according to Embodiment 1.

(3) Indication number in the FIG: 1ion source, 2guide rod, 3detector, 4ion trap, 5mechanical pump, 6turbopump, 7cooling gas

(4) FIG. 3 is the diagram for ion restricted square wave voltage and dipolar excitation square wave voltage imposed according to Embodiment 1.

(5) FIG. 4 is the mass spectrogram showing experimental results and selective isolation of parent ions according to Embodiment 1; selected sample is Reserpine (m/z=609).

(6) FIG. 5 is the mass spectrogram showing experimental results of Embodiment 1 and collision induced disassociation realized by resonance collision of ions through change of cycle of square wave voltage; value is 0.3478; duration is 40 ms; cycle (a), (b), (c) and (d) is 1.450 s, 1.46 s, 1.465 s and 1.470 s respectively.

(7) FIG. 6 is the diagram showing conventional sine wave voltage used to drive ion trap and dipolar excitation voltage imposed in the same manner as ion restricted voltage and dipolar excitation voltage when sine wave is used.

(8) FIG. 7 is the diagram showing digital square wave voltage used to drive ion trap and dipolar excitation voltage imposed in the same manner as ion restricted voltage and dipolar excitation voltage when digital square wave is used.

PREFERRED EMBODIMENTS

Embodiment 1

(9) This technical solution makes use of digital square wave to drive ion trap, which is expected to realize collision induced disassociation by changing cycle of dipolar excitation voltage; experimental verification has been carried out to this solution, of which specific contents are stated as follows:

(10) According to this solution, rectangular ion trap is selected for test. Instrument experiment platform is as shown in FIG. 2, which comprises electrospray ionization source-rectangular ion trap mass spectrometry system (ESI-RIT-MS) independently designed and fabricated by our laboratory. This instrument comprises three-stage differential vacuum system; vacuity inside the third-stage vacuum cavity where ion trap is located is up to 310.sup.3 Pa. ions produced by electrospray ionization source come into the two-stage vacuum cavity via the sampling cone, which will be further delivered to the rectangular ion trap by a 200 mm long quadrupole ion to complete mass analysis. Helium, the cooling gas is to be introduced from the small hole on the electrode of rear cover of the ion trap for cooling of ions. Reagent used is Reserpine (m/z=175) that is made into 510.sup.5 M solution by Shanghai Aladdin Reagent Co., Ltd; selected solvent is 50:50 methanol, containing 0.05% acetic acid.

(11) Square wave voltage of low electrical level, namely 5V TTL electrical level is to be produced by means of direct digital synthesis (DDS). Continuously adjustable high-voltage square wave with amplitude of 0-500 v.sub.0-p, is obtained through amplification with quick switches and MOSFET field effect tube, which is to be used as restriction voltage. Dipolar excitation voltage is to be obtained through frequency division of restriction voltage; in other words, there exists a proportional relationship between frequency of dipolar excitation voltage and that of restriction voltage; the coefficient is /2, wherein value is lower than 1. in other words, it is applicable to further change cycle of dipolar excitation voltage signals by changing restriction voltage signals. Cycle, sweep rate, symmetry and time sequence is available for precise control with software. The mode in which square wave voltage is imposed on rectangular ion trap is as shown in FIG. 3. A pair of square wave restricted voltage of the same amplitude and thoroughly different phase is to be imposed on two pairs of electrodes in the Direction x and y of ion trap. Ions are ejected in the direction x; whereas coupled dipolar excitation voltage and square wave restricted voltage is imposed to a pair of electrodes in direction x.

(12) It is applicable to obtain a complete spectrogram of sampled ions through conventional mass scanning. Under such circumstance, dipolar excitation voltage is in symmetrical wave form with frequency equivalent to of that of restricted square wave; in other words, value is ; whereas amplitude is a set value. Accompanied by scanning of frequency of restriction square wave, ions of different mass-to-charge ratios will subject to resonance at the resonance point in proper sequence, which will be detected by ion detector one ejected from the ion trap. Tandem mass spectrometry analysis is divided into three stages in terms of time.

(13) At the first stage of tandem mass spectrometric analysis, Reserpine ion is to be isolated for cooling before being restricted in the ion trap; under such circumstance, dipolar excitation voltage is not imposed. At this point, mass scanning is to be carried out following this stage to obtain a spectrogram comprising 609 mass spectral peaks as shown in FIG. 4.

(14) At the second stage of mass spectrometric analysis, cycle of restriction voltage is to be further changed by changing that of dipolar excitation voltage; meanwhile, such voltage is in symmetrical wave form; its duty ratio is 50%; whereas its amplitude remains unchanged. Value is a certain value lower than 1; under the action of periodic change of dipolar excitation voltage, parent ion will subject to disassociation to obtain fragment ions to be restricted through cooling. Cycle of restriction voltage signals is changed by software.

(15) At the third stage of tandem mass spectrometric analysis, dipolar excitation voltage is in symmetrical wave form; in other words, duty ratio is 50%, and value is . Fragment ions will subject to resonance under the action of dipolar excitation voltage; eventually, fragment ions ejected from the lead-out hole or groove on the electrode are to be detected to complete tandem mass spectrometric analysis.

(16) As indicated by preliminary experimental results, at the second stage of tandem mass spectrometric analysis, namely collision induced disassociation stage, parent Reserpine ions will subject to fragmentation to some extent when value is fixed to 0.3478, and the cycle of restriction voltage signals is up to 1.450 s, 1.460 s, 1.465 s and 1.470 s respectively. See FIG. 5(a)-(d).

(17) According to this invention, it is applicable to use conventional sine wave voltage to drive ion trap; sine wave is also applicable to dipolar excitation voltage; it is also applicable to make use of resonance collision energy of ions produced by changing cycle of dipolar excitation voltage to realize collision induced disassociation of parent ions. Radio frequency voltage and dipolar excitation voltage imposed are as shown in FIG. 6.

(18) According to this invention, ion trap with hyperbolic electrodes is used; it is applicable to select 3D ion trap or linear ion trap with hyperbolic electrodes; central sectional structure of the two is identical; radio frequency voltage and dipolar excitation voltage imposed are as shown in FIG. 7; it is also applicable to impose a pair of digital square wave voltage of the same amplitude and thoroughly different phase to two pairs of electrodes in direction x and y of hyperbolic ion trap respectively; this aims to realize collision induced disassociation of parent ions by changing cycle of dipolar excitation voltage signals.