JP5953153B2 - Mass spectrometer - Google Patents

Description

  The present invention relates to a mass spectrometer provided with a sample separation means and a mass analysis means.

  A mass spectrometer is an instrument that ionizes sample molecules, separates the generated ions into a mass-to-charge ratio by an electric field or a magnetic field, and measures the amount with a detector. And it is the method of analyzing a compound from the detected mass spectrum.

  One of the mass spectrometry measurements is known as MS / MS analysis. In this method, specific ions are selected, the selected ions are fragmented by collision with a gas or the like, and specific ions are selected again from the fragmented ions to obtain data with less background. As an MS / MS type mass spectrometer, there is an apparatus called a triple quadrupole type that detects a ion by generating a quadrupole electric field in a mass separator and vibrating the ion in the electric field.

  This triple quadrupole mass spectrometer is shown in FIG. The triple quadrupole mass spectrometer is composed of a sample introduction unit 1, an ion source unit 2, a mass separation unit 3, and a detector 4, and the sample introduction unit 1 from a liquid chromatograph (LC), gas chromatograph (GC), etc. A measurement sample is introduced into the ion source, and the measurement sample is ionized by the ion source unit 2. The mass separation unit 3 is composed of three stages of quadrupole electrodes each composed of four opposing cylindrical electrodes. The first-stage quadrupole electrode (Q1) 11 and the third-stage quadrupole electrode (Q3) 13 function as mass filters for selecting ions, and the second-stage quadrupole electrode (Q2) 12 is the collision chamber 5 (collision). Cell). Then, the detector 4 outputs a detection signal corresponding to the ion amount.

  The user sets measurement conditions from the input unit 101 and sets measurement target ions. The measurement target ions are converted into a set voltage by the control unit 102, and the high frequency voltage / DC voltage generation unit 103 is controlled to apply the DC voltage U and the high frequency voltage V to each electrode. The detection signal measured by the detection unit 4 is sent to the control unit 102, and the measurement result is displayed on the input unit 101.

  A DC voltage and a high-frequency voltage are applied to the first-stage quadrupole electrode (Q1) 11. Due to the action of the generated electric field, only ions having a specific mass-to-charge ratio to be measured among various ions generated in the ion source 2 pass as precursor ions.

  The second-stage quadrupole electrode (Q2) 12 is housed in the collision cell 5 for the purpose of causing collision-induced dissociation (CID), and for example, nitrogen ( CID gas 6 such as N2) has been introduced. Usually, in the second-stage quadrupole electrode (Q2) 12, only a high-frequency voltage is generally applied, and energy necessary for ion dissociation is given to the ions. Precursor ions incident on the second-stage quadrupole electrode (Q2) 12 become product ions due to collision with the CID gas 6. Plural types of product ions with different mass-to-charge ratios are generated from the precursor ions and introduced into the third-stage quadrupole electrode (Q3) 13.

  Like the first-stage quadrupole electrode (Q1) 11, the third-stage quadrupole electrode (Q3) 13 is applied with a DC voltage and a high-frequency voltage, and is generated in the collision cell 5 by the action of the generated electric field. Of the various ions, only product ions having a specific mass-to-charge ratio to be measured reach the detector.

  The voltage applied to the electrode will be described. The quadrupole mass spectrometer is applied by applying equation (1) to the opposing pole electrodes of the first-stage quadrupole electrode (Q1) 11 and the third-stage quadrupole electrode (Q3) 13. Of the ions, only specific ions can pass through and reach the detector 4.

  The quadrupole mass spectrometer can determine the value of ± (direct current + high frequency voltage) for specific ions based on the stable region of the Mathieu diagram shown in FIG. 2 (Patent Document 1). The vertical axis a and the horizontal axis q in FIG. 2 are obtained from equations (2) and (3), respectively.

Where m is the mass of the ion, e is the charge amount of the ion, r0 is the inner radius of the quadrupole electrode, and (4) is the angular frequency of the high-frequency voltage.

  Next, there is a technique called MRM (Multiple Reaction Monitoring) as a method for specifically quantifying a specific component contained in a complex sample.

A characteristic product obtained by CID by fixing the first-stage quadrupole electrode (Q1) 11 to the mass-to-charge ratio of the desired precursor ion and further performing the CID reaction with the second-stage quadrupole electrode (Q2) 12 In this method, ions are fixed in mass at the third-stage quadrupole electrode (Q3) 13 for measurement. Since the ions after the CID reaction are selected, it is possible to simplify the sample pretreatment before introducing the MS. MRM is SIM (Selected Ion
Compared to Monitoring, the absolute sensitivity is reduced, but the selectivity is dramatically improved, and noise such as contaminating ions can be made extremely small, enabling measurement with higher sensitivity than SIM. .

  In MRM measurement, measurement is sequentially performed for each precursor ion and product ion to be measured based on measurement items set in advance by the user.

JP-A-8-77963 Japanese Unexamined Patent Publication No. 7-201304

  However, in MRM measurement, the precursor ions to be measured next are introduced into the collision cell with the product ions generated from the precursor ions to be measured currently remaining in the collision cell. Product ions may be mixed.

  This is a phenomenon called crosstalk in MS / MS analysis, and the presence of crosstalk deteriorates the quantitativeness of the target component.

  In order to prevent this crosstalk, a method in which a measurement is not performed until all ions in the collision cell are discharged, a voltage in the collision cell is changed to a non-measurement voltage such as 0 V, etc. There is a method of forcibly discharging ions in the collision cell by this method. However, when the measurement suspension period is provided, the suspension period is a wasteful time in measurement, and the measurement throughput is reduced. In addition, if the pause period is short, the amount of ions incident on the detector may not be sufficiently recovered at the start of the next detection period for collecting data. In the early stage of the measurement, the sensitivity of measurement is lowered. Also, for example, when the voltage is changed to a non-measurement voltage such as 0 V, when a voltage corresponding to the next measurement target ion is applied after the change of 0 V, overshoot (undershoot) or ringing occurs particularly in the high-frequency voltage. In addition, a waiting time (settling time) until the voltage after voltage change becomes stable is required, and ions are detected with respect to the applied voltage after the settling time has elapsed. Therefore, the longer the settling time, the longer the measurement time interval, the lower the time resolution, and the lower the throughput.

  In the mass spectrometer described in Patent Document 2, a pulse voltage is applied to the lens electrodes on the entrance side and the exit side of the collision cell during the pause period in which the mass-to-charge ratio of the precursor ion is switched, thereby temporarily in the collision cell. The ions are attracted to and collide with the lens electrode by the action of the electric field formed on the surface.

  However, if a pulse voltage for ion removal is applied to the lens electrode while a large amount of ions remain in the collision cell, the amount of ions that collide with the lens electrode is large, and the lens electrode is contaminated. In addition, the structure becomes complicated, and the control becomes complicated due to the increase in the device price and the increase in the number of objects to be controlled.

  The present invention has been made to solve the above-described problems, and the object of the present invention is to perform ions remaining in the collision cell at the time of switching the measurement sample without reducing the throughput when performing MRM measurement. An object of the present invention is to provide a mass spectrometer for removing the influence of crosstalk generated by the above.

  The mass spectrometer of the present invention applies the destabilization voltage calculated from the Mathieu diagram destabilization region before applying a predetermined voltage to the ions to be measured.

  According to the present invention, the influence of crosstalk generated in the collision cell can be removed and the settling time can be shortened.

1 is an overall configuration diagram of a triple quadrupole mass spectrometer. It is explanatory drawing of a Mathieu diagram. It is a reading flowchart of the user setting item of this apparatus. It is a setting flowchart of Exhaust Voltage of the present invention. It is a comparative example of the present invention, and is an explanatory diagram of a crosstalk removal method when changed to 0V. It is explanatory drawing of the crosstalk removal method at the time of using Exhaust Voltage.

  Examples of the present invention will be described.

  As shown in FIG. 3, the apparatus user previously creates a file for determining each measurement condition from a graphic user interface (GUI) when performing measurement. The measurement condition settings include measurement schedule, device condition setting, channel number setting, channel condition item setting, scan mode condition determination, calibration file designation, and the like.

  Since there are various setting items, the file structure is divided into the following four types. There are four types of files: Sample Table File (301), Data Acquisition File (302), Method File (303), and Calibration File (304).

  Sample Table File (301) is a file that lists the ions to be measured, and is a list of mass separations performed in the MS filter of the first quadrupole electrode (Q1) 11 and the third quadrupole electrode (Q3) 13. It is. That is, the Sample Table File (301) is a file for determining a measurement schedule, and is a file for setting a measurement sequence in order to support continuous measurement of a plurality of samples.

  A file for specifying measurement conditions for each sample in the Sample Table File (301) is a Data Acquisition File (302).

  In the Data Acquisition File (302), there are a Method File (303) and a Calibration File (304) for performing mass correction of each channel as condition files for each channel. The calibration file (304) refers to the scan mode contents and polarity contents specified in each channel, and calibration is optimal for the first quadrupole electrode (Q1) 11 and the third quadrupole electrode (Q3) 13. Use content.

  From the above files, a schedule file (Voltage Schedule File (305)) of voltages to be applied to all electrodes is created. The triple quadrupole mass spectrometer reads this Voltage Schedule File (305) and applies a voltage to each electrode as needed.

  Next, the Exhaust Voltage (Ve) that is inserted between the first measurement target ion voltage and the second measurement target ion and discharges the product ions from the collision cell when switching the measurement target ions will be described.

  Generally, in the triple quadrupole mass spectrometer, only the high-frequency voltage applied to the third-stage quadrupole electrode (Q3) 13 and the high-frequency voltage obtained by removing the DC voltage from the high-frequency voltage is the second-stage quadrupole electrode. (Q2) Applied to 12. This is because the voltage deviation between the second-stage quadrupole electrode (Q2) 12 and the third-stage quadrupole electrode (Q3) 13 is eliminated, and the ion trapping potential in Q2 can be optimized. This is because the number of power supplies can be reduced. Since the measurement is performed so as to correspond to the vicinity of the top of the Matthew diagram, a high-frequency voltage of q = 0.706 is applied to the second-stage quadrupole electrode 12 (Q2) from the Matthew diagram. If the high-frequency voltage exceeds q = 0.908, ions cannot pass through regardless of the value of the DC voltage a. The high-frequency voltage that cannot pass through is called a cut-off voltage.

  As shown in FIG. 4, this mass spectrometry system reads measurement information from each file set in advance by the user, and sets this Exhaust Voltage between the first measurement target ion and the second measurement target ion to the Voltage Schedule File. Insert automatically at (305).

  In step S401, the mass spectrometry system reads the first measurement target ion (M1). Next, in step S402, the voltage (V1) corresponding to the first measurement target ion is calculated from the apparatus setting value and described in the Voltage Schedule File (305) (step S403).

  Next, in step S404, the second measurement target ion (M2) is read, and in step S405, the voltage (V2) corresponding to the second measurement target ion is calculated from the apparatus setting value. In step S406, the destabilization voltage (Ve2) of the second measurement target ion is calculated, and in step S407, it is written in the Voltage Schedule File (305). In step S408, the measurement voltage calculated in step S405 is described in the Voltage Schedule File (305). When subsequent measurement target ions are set, the operations from step 404 to step S408 are sequentially repeated, and similarly described in the Voltage Schedule File (305).

  The voltage shown in FIGS. 5 and 6 is the time change of the voltage applied to the second-stage quadrupole electrode (Q2) 12. In MRM measurement, the first stage quadrupole electrode (Q1) 11 switches the setting from the first measurement target ion (M1 ′) to the second measurement target ion (M2 ′), and the third stage quadrupole electrode 13 When the mass separation target ion in (Q3) is fixed to M1, the voltage value V1 corresponding to M1 is applied to the second-stage quadrupole electrode 12 (Q2).

  The product ion M1 generated from the first measurement target ion (M1 ') is measured until time t1, and the product ion M1 generated from the second measurement target ion (M2') is measured from time t2.

  FIG. 5 shows a comparative example of the present invention, in which 0 V is applied to the second-stage quadrupole electrode to eliminate crosstalk, and ions remaining in the collision cell (collision chamber) are discharged. The voltage applied to the second-stage quadrupole electrode changes to 0V, and then changes again to the product ion voltage value V1 to be measured. At this time, the voltage fluctuation is ΔV1, and overshoot and ringing proportional to the voltage fluctuation width occur. The settling time at this time is ts1.

  FIG. 6 shows a case where an exhaust voltage is applied to the second-stage quadrupole electrode (Q2) 12 in order to eliminate crosstalk. The Exhaust Voltage is about 1.3 times (= 0.908 / 0.706) the voltage to be measured V1 in the Matthew diagram of FIG. 2, and the voltage fluctuation is ΔV2.

  Since ΔV2 is about 0.3 times ΔV1, it is relatively smaller than when the voltage fluctuation range is changed to 0 V (comparative example shown in FIG. 5). In general, when the voltage is varied, the smaller the variation voltage width (ΔV), the smaller the overshoot (undershoot) and ringing, so that the settling time can be shortened. That is, since the settling time satisfies ts1> ts2, the throughput can be improved when crosstalk is removed using the exhaust voltage than when the crosstalk is changed to 0V.

  Similarly, when the mass separation target ion (product ion) at the third-stage quadrupole electrode (Q3) 13 is changed from M1 to M2, it is also affected by applying a cut-off voltage value higher than the product ion (M2). Can be removed.

  If the Exhaust Voltage is equal to or higher than the Cutoff voltage value, residual ions can be removed from the collision cell. However, if the Exhaust Voltage exceeds 2.0 times, the voltage fluctuation will be the same as when the voltage is changed to 0 V. Voltage should be 1.3 times or more and less than 2.0 times.

  The Exhaust Voltage is automatically described in the Voltage Schedule File (305), but it may be able to be confirmed directly by the user, even if the user changes the set value for the purpose of optimizing the settling time. good.

  In Example 1, the voltage applied to the second-stage quadrupole electrode (Q2) 12 is a high-frequency voltage. However, when a DC voltage can also be applied, the Matthew diagram shows an unstable region. Thus, product ions can be eliminated in the same manner.

  When a high frequency voltage is generated using a resonance circuit or the like, generally, the settling time is longer when the high frequency voltage is varied than when the DC voltage is varied. In some cases, it is technically difficult to increase the high-frequency voltage. In such a case, it is easier to change the a value by the DC voltage, and the settling time can be shortened.

  From the above-mentioned Matthew diagram, when the value of the high-frequency voltage is constant at q = 0.706, the residual ions can be eliminated from the collision cell (collision chamber) by setting the DC voltage value a to 0.237 or more. is there.

  This may be changed in combination with the high-frequency voltage, and the applied DC voltage and high-frequency voltage may be changed to the Matthew diagram unstable region in order to optimize the settling time.

  Similar to the case where the DC voltage and the high frequency voltage are applied to the second stage quadrupole electrode (Q2) 12 shown in Example 2, the DC voltage and the high frequency voltage of the first stage quadrupole electrode (Q1) 11 are unstable regions. Since the precursor ions introduced through the first-stage quadrupole electrode (Q1) 11 and introduced into the collision cell (collision chamber) are eliminated, the influence of crosstalk can be reduced.

  This is because the precursor ions introduced into the second-stage quadrupole electrode (Q2) 12 are eliminated, so that product ions cannot be generated, and the influence of crosstalk can be eliminated.

  Similarly to the first and second embodiments, a single DC voltage or high-frequency voltage may be used alone or may be combined and changed to the Matthew diagram unstable region.

  As a method for discharging the ions in the collision cell shown in the first embodiment, another electrode such as a quadrupole electrode may be disposed after the second-stage quadrupole electrode (Q2) 12. Alternatively, a voltage may be applied by arranging another electrode such as a quadrupole electrode, for example, before the third-stage quadrupole electrode (Q3) 13 outside the collision cell.

  In order to eliminate the precursor ions introduced into the collision cell shown in Example 3, another electrode such as a quadrupole electrode may be disposed after the first-stage quadrupole electrode (Q1) 11. Second stage quadrupole electrode (Q2) 12 Another electrode such as a quadrupole electrode may be arranged in the preceding stage.

  The voltage applied to the above-mentioned separate electrodes is supplied from a power source separate from the first-stage quadrupole electrode (Q1) 11, the second-stage quadrupole electrode (Q2) 12, and the third-stage quadrupole electrode (Q3) 13. Alternatively, a voltage having an unstable voltage value may be temporarily applied.

DESCRIPTION OF SYMBOLS 1 Sample introduction part 2 Ion source part 3 Mass separation part 4 Detection part 5 Collision chamber 6 CID gas
11 First stage quadrupole electrode (Q1)
12 Second stage quadrupole electrode (Q2)
13 Third stage quadrupole electrode (Q3)
101 Input section
102 Control unit
103 High-frequency / DC voltage generator
301 Sample Table File
302 Data Acquisition File
303 Method File
304 Calibration File
305 Voltage Schedule File

Claims (15)

A plurality of products generated by the dissociation of the precursor ions, a first mass analysis unit that applies a DC voltage and a high-frequency voltage to select specific precursor ions, a collision chamber having an electrode for dissociating the precursor ions, and In a mass spectrometer having a second mass analyzer that selects only desired ions from ions, and a detector that detects product ions selected by the second mass analyzer,
Calculated from the Mathieu diagram destabilized region at the timing of switching from the first measurement target ion to the second measurement target ion and before applying a predetermined voltage to the second measurement target ion A mass spectrometer characterized by applying an unstable voltage. In claim 1,
The first mass analyzer, the collision chamber, and the second mass analyzer are each provided with four pole-shaped electrodes. In claim 2 ,
A mass spectrometer characterized in that a high-frequency voltage applied to the collision chamber electrode is equal to or higher than a Cutoff voltage value of the product ion. In claim 2 ,
A mass spectrometer characterized in that a DC voltage applied to the collision chamber electrode is an unstable voltage of the product ion. In claim 2 ,
A high-frequency voltage applied to the first mass analyzer is a destabilizing voltage value of a precursor ion. In claim 2 ,
A mass spectrometer that prevents the precursor ions from being mixed into the collision chamber by setting the DC voltage applied to the first mass spectrometer to a value equal to or higher than the destabilization voltage value of the precursor ions. In claim 3 ,
A mass spectrometer, further comprising another electrode disposed behind the collision chamber electrode, and applying a destabilizing voltage to the other electrode. In claim 7 ,
The mass spectrometer is characterized in that the separate electrodes are four pole-shaped electrodes. In claim 3 ,
A mass spectrometer characterized in that another electrode is arranged in front of the second mass spectrometer and an instability voltage is applied to the other electrode. In Claim 9 , The said another electrode is four pole-shaped electrodes, The mass spectrometer characterized by the above-mentioned . In claim 5 ,
A mass spectrometer characterized in that another electrode is disposed after the first mass spectrometer and an instability voltage is applied to the other electrode. In claim 11 ,
The mass spectrometer is characterized in that the separate electrodes are four pole-shaped electrodes. In claim 5 ,
A mass spectrometer characterized in that another electrode is arranged in front of the second mass spectrometer and an instability voltage is applied to the other electrode. In claim 13 ,
The mass spectrometer is characterized in that the separate electrodes are four pole-shaped electrodes. In claim 3 ,
The mass spectrometer is characterized in that the high-frequency voltage is 1.3 times or more and less than 2.0 times the Cutoff voltage of product ions.