CN102103974B - Method and device for enhancing CID (Collision Induced Dissociation) property of ion trap - Google Patents

Abstract

The invention relates to a method for enhancing the CID (Collision Induced Dissociation) property of an ion trap. The ion trap comprises a terminal electrode. The method is characterized in that a voltage signal applied to the terminal electrode contains multiple frequency components in the CID process of ions, wherein the multiple frequency components include frequency components positioned in [(f-1)kHz, (f+1)kHz], and f(kHz) is the resonance frequency of the ions which are to be subjected to CID; and the voltage signal is a broadband signal containing all the frequency components within a certain frequency range and can be also a swept-frequency signal with frequency changed with time. The invention also provides a device for enhancing the CID property of the ion trap. The invention can eliminate the influence brought about in such a way that space charge effect or radio frequency restrains voltage fluctuation, and the like, thereby enhancing the CID efficiency and repeatability.

Description

A kind of method and device that improves ion trap collision induced dissociation performance

Technical field

The present invention relates to a kind of method and device that improves the ion trap performance, especially a kind of method and device that improves ion trap collision induced dissociation performance.

Background technology

The multi-stage ms analysis is a critical function of ion trap mass spectrometer, has very important status in the fields such as the genomics that relates to structure of matter analysis, protein science and pharmacy.Simultaneously, the multi-stage ms analytic function is that ion trap mass spectrometer is with respect to one of other mass spectrometric advantages.

The multi-stage ms analytic process is as follows: at first by object ion (or parent ion) is isolated, then by collision induced dissociation (Collision Induced Dissociation, CID) make the parent ion cracking, the fragment ion that obtains after the cracking is called as daughter ion.Daughter ion also can carry out identical isolation and CID process.By just can analyze the structure of ion to the fragment ion that obtains behind the ion CID, obtain more substantial information.

At present, the ion trap theory is very ripe, only briefly introduces the theory relevant with CID here.For one radially radius be r ₀, axial radii is z ₀Three-dimensional ion trap, its stability diagram parameter a _zAnd q _zBe defined as follows:

$a_z=\frac{-16\mathrm{eU}}{m(r_0^2+{2z}_0^2){\mathrm{\Ω}}^2}---\left(1\right)$

$q_z=\frac{8\mathrm{eV}}{m(r_0^2+{2z}_0^2){\mathrm{\Ω}}^2}---\left(2\right)$

Wherein fetter parameter and comprise the direct voltage U that applies on the ion trap electrodes, the angular frequency Ω of the amplitude V of radio-frequency voltage and radio-frequency voltage.

Resonance frequency ω (secular frequency be denoted as ω) and a of ion in ion trap _zAnd q _zDirectly related, generally introduce the relation that parameter beta is described ion resonance frequency and radio-frequency voltage frequency omega, be shown below:

$\mathrm{\ω}=\frac{1}{2}\mathrm{\β\Ω}---\left(3\right)$

$\mathrm{\β}\≈\sqrt{(a+\frac{q^2}{2})}---\left(4\right)$

Can find out from top analysis, in the three-dimensional ion trap that physical dimension is determined, in the situation that the constraint parameter is certain, the ion of different mass-to-charge ratioes has different resonance frequencys.

The basic principle of CID is as follows: the amplitude of the RF that applies on ion trap ring electrode constraint voltage and frequency one regularly are stored in ion in the ion trap and all have separately resonance frequency.When the endcap electrode of ion trap applied the excitation signal identical with the ion resonance frequency, ion can resonate.Ion will absorb the energy of external excitation signal in resonance process, be converted into kinetic energy; Simultaneously, energy in a part of kinetic transformation can being become in the collision process that buffer gas occurs in ion and the ion trap, when ion and buffer gas constantly bump, interior can increase to the chemical bond energy that overcomes ion inside the time, this ion will dissociate, and forms daughter ion.

CID efficient and repeatability are the key factors that determines the multi-stage ms analytical performance.

At present, the CID method of most of ion trap mass spectrometers employings as shown in Figure 2.In the CID process, RF constraint voltage keeps constant, applies a single frequency sinusoidal ripple identical with the ion resonance frequency ion is dissociated.And in fact, the resonance frequency of ion is subject to the impact of several factors, and the rounding error that brings such as space charge effect, RF constraint voltage fluctuation, variations in temperature and calculating all may make the resonance frequency of the excitation signal frequency departure ion that adds.Therefore, use CID mode as shown in Figure 2 can not guarantee efficient and the repeatability of CID.

For addressing the above problem, the Varian mass spectrometer has adopted CID method as shown in Figure 3.It is by the amplitude of RF constraint voltage is modulated, to reach the warbled purpose of ion resonance.That is to say, the resonance frequency of ion will change within the specific limits, and the excitation signal frequency that the outside applies only need drop in this frequency range and get final product.The method has improved efficient and the repeatability of CID to a certain extent, but there is following shortcoming in it:

1) as shown in Figure 3, the RF amplitude modulation approach is actually at the RF signal modulation signal that superposeed.Because the RF circuit is generally the LC resonant circuit, so circuit has the frequency-selecting function, this so that the frequency of modulation signal be restricted.

2) the high-voltage radio-frequency signal is modulated to be caused output voltage fluctuation, also increased the difficulty that circuit is realized.

3) certain even RF is carried out the scope of amplitude modulation(PAM), its scope that causes the ion characteristic frequency change is different to the ion of different mass-to-charge ratioes.That is to say that there is " quality discrimination " effect in the method.

Summary of the invention

For solving the deficiencies in the prior art, the present invention proposes a kind of method of the CID of raising performance.The method can be eliminated the impact that space charge effect or radio frequency constraint voltage fluctuation etc. bring, and improves CID efficient and repeatability.

For achieving the above object, the present invention is by the following technical solutions:

A kind of method that improves ion trap collision induced dissociation performance, described ion trap comprises termination electrode; Characteristics are:

Ion is carried out in the process of CID, the voltage signal that is applied on the described termination electrode comprises two or more frequency contents, wherein have the frequency content that is in [(f-1) kHz, (f+1) kHz], f (kHz) is the resonance frequency that will carry out the ion of CID.

Further, described voltage signal is the broadband signal with frequency range, and this broadband signal has comprised all frequency contents in this frequency range.

As preferably, described voltage signal can obtain by white noise signal is carried out bandpass filtering.

Further, in described voltage signal, frequency content disperses.

Further, described voltage signal is the time dependent swept-frequency signal of frequency, and the initial frequency of swept-frequency signal and termination frequency can be set.

Further, in the CID process, described swept-frequency signal occurs more than twice or twice.

Further, the time dependent relation of frequency is linear or nonlinear.

Further, when the time dependent relation of frequency when being non-linear, to each frequency content setup times weight.

Further, the time weighting with the high frequency content of the resonance frequency equal probability of ion is larger than other frequency content.

In order to realize said method, the invention allows for a kind of like this device that improves ion trap collision induced dissociation performance, described ion trap comprises termination electrode, described device comprises:

Signal generator, the voltage signal that signal generator produces is applied on the described termination electrode; Described two or more frequency contents of voltage signal bag wherein have the frequency content that is in [(f-1) kHz, (f+1) kHz], and f (kHz) is the resonance frequency that will carry out the ion of CID.

Further, described voltage signal is the broadband signal with frequency range, and this broadband signal has comprised all frequency contents in this frequency range.

Further, in described voltage signal, frequency content disperses.

Further, described voltage signal is the time dependent swept-frequency signal of frequency, and the initial frequency of swept-frequency signal and termination frequency can be set.

Further, in the CID process, described swept-frequency signal occurs more than twice or twice.

Further, the time dependent relation of frequency is linear or nonlinear.

Further, when the time dependent relation of frequency when being non-linear, to each frequency content setup times weight.

Further, the time weighting with the high frequency content of the resonance frequency equal probability of ion is larger than other frequency content.

Compared with prior art, advantage of the present invention is:

1, carries out in the process of CID at ion, apply a voltage signal with certain frequency scope on the ion trap endcap electrode, even the factors such as space charge effect or constraint voltage drift cause variation of resonant frequency, the frequency range of voltage signal also can contain this resonance frequency.This has eliminated the impact that the ion resonance frequency is brought owing to some factors vary, has improved the repeatability of CID.

2, in the CID process, the ion outgoing and the ionic dissociation process that are caused by resonant excitation are mutually " competitions ".Under traditional approach, ion continues to be subject to resonant excitation, and its Oscillation Amplitude may continue to increase and flee from the constraint of ion trap.And in the present invention, ion just periodically is subject to resonant excitation, so ion has sufficient time and buffer gas to bump, and the kinetic energy of acquisition is converted to interior energy.Therefore, the method has improved CID efficient.

3, employing is carried out frequency modulation(FM) to outside excitation signal, and warbled scope can be adjusted according to the mass-to-charge ratio of ion, eliminates " quality discrimination ".

4, the weight of the frequency content of voltage signal is adjustable, guarantees to improve in the CID efficient situation to reduce the CID required time.

5, this voltage signal belongs to low-voltage and low frequency signal, controls this voltage signal and more easily realizes than the RF signal of control high pressure, and is also more flexible.

Description of drawings

Fig. 1 is the structural representation of ion trap mass spectrometer;

Fig. 2 is the sequential chart of traditional CID;

Fig. 3 is the sequential chart of the CID of Varian mass spectrometer employing;

Fig. 4 is the sequential chart of the CID that adopts of the present invention, and wherein the CID voltage signal is broadband signal;

Fig. 5 is the sequential chart of the CID that adopts of the present invention, and wherein the CID voltage signal is the time dependent swept-frequency signal of frequency;

Fig. 6 is the mass spectrometric working timing figure of the embodiment of the invention 1 intermediate ion trap.

Embodiment

Embodiment 1:

A kind of device that improves ion trap collision induced dissociation performance is applied in the ion trap mass spectrometer.

As shown in Figure 1, described ion trap mass spectrometer comprises three-dimensional ion trap, electron source 106, electronic gate 104, ion detector 105, radio freqnency generator 109.Described ion trap comprises ring electrode 101, termination electrode 102,103.Mass spectrometer applies radio frequency constraint voltage on the ring electrode 101 when work, radio frequency constraint voltage is produced by radio freqnency generator 109.

Described device comprises signal generator 107, and the voltage signal of generation is converted to double-end signal through transformer, is applied to respectively on the termination electrode 102,103.As shown in Figure 4, described voltage signal is a broadband signal, and its frequency range is (f-2) kHz-(f+2) kHz, and namely it has comprised all frequency contents in this frequency range.Wherein f (kHz) is the ion resonance frequency that calculates according to radio frequency constraint voltage and relevant parameter theory.Described voltage signal obtains by white noise is carried out bandpass filtering.

The present embodiment has also disclosed a kind of method that improves ion trap collision induced dissociation performance, is applied in the multi-stage ms analysis, and as shown in Figure 6, the multi-stage ms analysis may further comprise the steps:

1, the ionization stage:

Apply all certain radio frequency constraint voltage of an amplitude and frequency on the electrode 101, and apply a positive direct voltage on the electrode 104, the electronics of electron source 106 emissions can enter ion trap by electronic gate 104, neutral sample ionization in the ion trap is become ion, and the ion that obtains is bound in the ion trap under the effect of rf electric field;

2, ion cooling stage:

The radio frequency constraint voltage that applies on the electrode 101 remains unchanged, and applies a negative direct voltage on the electrode 104 simultaneously, stops electronics to enter ion trap; In this stage, the ion that is bound in the ion trap loses its kinetic energy gradually under the collision of buffer gas (He), thereby is gathered in the middle section of ion trap under the constraint effect of rf electric field;

3, quality isolation stage:

Radio frequency constraint voltage amplitude on the electrode 101 maintains a fixed value, and the size of voltage amplitude is set according to the mass-to-charge ratio that will isolate ion.Apply the SWIFT signal at electrode 102 and 103, this signal comprises the frequency content of 50～500kHz, comprises simultaneously a frequency disappearance window, the corresponding resonance frequency that needs the isolation ion of the frequency in this window; Behind the quality isolation stage, except interested ion (parent ion), other ion all is subject to resonant excitation, and to eject ion trap outer or impinge upon on the electrode of ion trap and bury in oblivion in the ion trap;

4, the CID stage:

Radio frequency constraint voltage amplitude on the electrode 101 is set according to the mass-to-charge ratio of parent ion, makes the q value (definition of q as shown in Equation 2) of parent ion between 0.2～0.45.Simultaneously apply voltage signal at endcap electrode 102 and 103, this voltage signal is a broadband signal, the concrete method that produces this signal is: (a) at first calculate the resonance frequency of ion according to radio frequency constraint voltage and relevant parameter theory, be designated as f (kHz); (b) calculate the CID voltage signal, the frequency range of this voltage signal be the kHz of (f-2) kHz～(f+2), and namely this voltage signal has comprised all the interior frequency contents of kHz of frequency range (f-2) kHz～(f+2); (c) use auxiliary signal generator 107 to produce above-mentioned voltage signal, by being loaded on electrode 102 and 103 after transformer 108 couplings.

The advantage that above-mentioned voltage signal brings is: (a) can eliminate the impact that the ion resonance frequency shift (FS) brings, improve the repeatability of CID.(b) ion is subject to intermittent exciting, and can be fully converts the kinetic energy of external excitation to interior energy, improves the efficient of CID.

5, the mass scanning stage:

The radio frequency constraint voltage that is applied on the electrode 101 is carried out linear scan, apply simultaneously the sinusoidal wave excitation signal of a fixed frequency at electrode 102 and 103.Ion will by its mass-to-charge ratio than successively outgoing from ion trap of size, after ion detector 105 detects, obtain final mass spectrogram in this process.

Embodiment 2:

A kind of device that improves ion trap collision induced dissociation performance, as different from Example 1:

1, the frequency content of the voltage signal of signal generator generation is discrete the distribution, in frequency range (f-2) kHz-(f+2) kHz, have (f-1.8) kHz, (f-1.6) kHz, (f-1.4) kHz ..., fkHz ... (f+1.4) kHz, (f+1.6) kHz, (f+1.8) kHz equifrequent.

2, the mode that does not recycle white noise filtering obtains above-mentioned voltage signal, and adopts other method.

A kind of method that improves ion trap collision induced dissociation performance, as different from Example 1:

1, the frequency content of the voltage signal of signal generator generation is discrete the distribution, in frequency range (f-2) kHz-(f+2) kHz, have (f-1.8) kHz, (f-1.6) kHz, (f-1.4) kHz ..., f kHz ... (f+1.4) kHz, (f+1.6) kHz, (f+1.8) kHz equifrequent.

2, the mode that does not recycle white noise filtering obtains above-mentioned voltage signal, and adopts other method.

Embodiment 3:

A kind of device that improves ion trap collision induced dissociation performance, as different from Example 1:

The frequency of the voltage signal that signal generator produces is linear change in time.As shown in Figure 5, this voltage signal is a frequency signal, and frequency range is (f-2) kHz-(f+2) kHz, and step-length is 200Hz, and the speed of initial frequency and frequency scanning is set according to actual conditions.In the CID process, this swept-frequency signal repeats, the time correlation that the number of times that repeats and sweep velocity and CID process continue.

A kind of method that improves ion trap collision induced dissociation performance, as different from Example 1:

The frequency that is applied to the voltage signal on the termination electrode is linear change in time, i.e. swept-frequency signal, and its frequency range is (f-2) kHz-(f+2) kHz, and step-length is 200Hz, and the speed of initial frequency and frequency scanning is set according to actual conditions.In the CID process, this swept-frequency signal repeats, the time correlation that the number of times that repeats and sweep velocity and CID process continue.

Embodiment 4:

A kind of device that improves ion trap collision induced dissociation performance, as different from Example 3:

The frequency of the voltage signal that signal generator produces is nonlinear change in time, frequency range is (f-2) kHz-(f+2) kHz, to each frequency content setup times weight, larger than other frequency content with the time weighting of the high frequency content of the resonance frequency equal probability of ion.

A kind of method that improves ion trap collision induced dissociation performance, as different from Example 3:

The frequency that is applied to the voltage signal on the termination electrode is nonlinear change in time, frequency range is (f-2) kHz-(f+2) kHz, to each frequency content setup times weight, larger than other frequency content with the time weighting of the high frequency content of the resonance frequency equal probability of ion.

Described weight can be arranged to adjustable, thereby has reduced the CID required time in raising CID efficient situation.

Above-mentioned execution mode should not be construed as limiting the scope of the invention.Key of the present invention is, the voltage signal that is applied on the ion trap termination electrode comprises two or more frequency contents, wherein have and be in [(f-1) kHz, (f+1) kHz] interior frequency content, f (kHz) is the resonance frequency that will carry out the ion of CID, described voltage signal can be a broadband signal that comprises all frequency contents in certain frequency range, also can be a time dependent swept-frequency signal of frequency.In the situation that do not break away from spirit of the present invention, any type of change that the present invention is made all should fall within protection scope of the present invention.

Claims (3)

1. method that improves ion trap collision induced dissociation performance, described ion trap comprises termination electrode; It is characterized in that:

Ion is carried out in the process of CID, the voltage signal that is applied on the described termination electrode comprises two or more frequency contents, wherein have the frequency content that is in [(f-1) kHz, (f+1) kHz], f is the resonance frequency that will carry out the ion of CID;

Described voltage signal is the broadband signal with frequency range, and this broadband signal has comprised all frequency contents in this frequency range.

2. the method for raising ion trap collision induced dissociation performance according to claim 1, it is characterized in that: described voltage signal can obtain by white noise signal is carried out bandpass filtering.

3. device that improves ion trap collision induced dissociation performance, described ion trap comprises termination electrode, described device comprises:

Signal generator, the voltage signal that signal generator produces is applied on the described termination electrode; Described voltage signal comprises two or more frequency contents, wherein has the frequency content that is in [(f-1) kHz, (f+1) kHz], and f is the resonance frequency that will carry out the ion of CID;

Described voltage signal is the broadband signal with frequency range, and this broadband signal has comprised all frequency contents in this frequency range.

Images