JP2892655B2 - Atmospheric pressure ionization mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to Atmospheric Pressure Ionization.
onization).

2. Description of the Related Art A mass spectrometer is a device that ionizes a sample, guides the sample to a high vacuum chamber, and performs mass separation to obtain a mass spectrum. Atmospheric pressure ionization mass spectrometers that ionize a sample under atmospheric pressure have come to be widely used.
In particular, those which ionize a sample by applying a voltage to a needle-shaped electrode under atmospheric pressure and discharging the same are often used.

In an atmospheric pressure ionization mass spectrometer, a sample ionized under atmospheric pressure is guided to a high vacuum mass spectrometer, so that adiabatic expansion occurs on the way to cool sample ions. When the sample ions are cooled and water or the like adheres to the surroundings, so-called cluster ions are formed, and the accuracy of mass spectrometry decreases. for that reason,
An intermediate pressure chamber is provided between atmospheric pressure and high vacuum to accelerate sample ions and collide with neutral particles to cleave cluster ions.

[Problems to be Solved by the Invention] However, in the above-described conventional technology, the stability of mass spectrometry or the relationship between the polarity of the voltage of the needle electrode and the cluster ion cleavage has not been sufficiently considered.

An object of the present invention is to provide an atmospheric pressure ionization mass spectrometer capable of performing stable and high-precision mass analysis by cleaving cluster ions even when the voltage state of the needle electrode is either positive or negative. is there.

[Means for Solving the Problems] In order to achieve the above object, according to the present invention, an intermediate pressure chamber having a pressure lower than the atmospheric pressure, a mass spectrometry chamber having a pressure lower than the intermediate pressure chamber, and a needle electrode are provided. An atmospheric pressure ionization mass spectrometer having atomizing means for atomizing a liquid containing a sample to generate a mist, and discharging the needle electrode under substantially atmospheric pressure to ionize the sample contained in the mist. Means for introducing the ionized sample to the mass spectrometer through the intermediate pressure chamber and performing mass analysis, wherein a means for switching a positive or negative voltage and supplying the voltage to the needle electrode, and at least the intermediate A first electrode and a second electrode disposed so as to face each other so as to sandwich a part of the pressure chamber, wherein the first electrode is disposed closer to the needle electrode than the second electrode; Is lower than the second electrode or the first electrode Means for supplying a voltage so that the electrode is higher than the second electrode, wherein the first electrode has a lower voltage than the second electrode when the needle electrode has a negative voltage. When the needle electrode is at a positive voltage, the first electrode is
The voltage was set higher than that of the electrodes.

[Operation] According to the above configuration, first, the liquid containing the sample is atomized, so that the liquid containing the sample becomes a mist state and is stabilized.
When a negative voltage is applied to the needle electrode, the sample contained in the liquid is ionized into negative ions, while when a positive voltage is applied to the needle electrode, the sample contained in the liquid becomes a positive ion. Ionized. Here, when a negative voltage is applied to the needle electrode, the first electrode is set to have a lower voltage than the second electrode, and the negative sample ions are accelerated in the intermediate pressure chamber and collide with neutral particles. . Even when a positive voltage is applied to the needle electrode, the liquid containing the sample is stable in an atomized state, and a positive voltage is applied to the needle electrode. It is ionized into ions. The first electrode is set higher than the second electrode, and positive sample ions are accelerated in the intermediate pressure chamber and collide with neutral particles.

Example First, in an example of the present invention, an LC / A
The outline will be described using a PI mass spectrometer as an example. The sample and the mobile phase eluted from the liquid chromatograph 1 (hereinafter abbreviated as LC) are sent to an atomizing section 3 through a Teflon pipe 2, where they are atomized by applying heat. The atomized sample and mobile phase are in a molecular state, and are ionized in the ionization chamber 4 by corona discharge generated by the needle electrode 5. The ionized mobile molecule undergoes a molecular reaction with the sample molecule, and the sample molecule is gently and almost all molecules are ionized by transferring the sample molecule heptron that has not been ionized. The ionized sample molecules pass through the first pore electrode 6 and further pass through the second pore electrode 7 to the mass analyzer 8 where they are subjected to mass analysis.

 Next, details will be described with reference to FIG.

The Teflon pipe 2 for guiding the sample or mobile phase eluted from the LC 1 is connected to a sample introduction pipe 10 by a joint 9, and the sample introduction pipe 10 is inserted into a heater block 11. Heater block 11 has heater 13 to heat it
A temperature detecting element 14 for detecting the temperature and the temperature is attached, and the sample or the mobile phase is stably and very finely mist (for example, as described in the “Aerosol” section of the supplementary edition of the third edition of the Iwanami Physical and Chemical Dictionary, The temperature is kept constant and constant so that the medium is a gas and the dispersed phase is a liquid (dispersed system) and is ejected from the tip of the sample introduction pipe 10.

The sample or mobile phase sent to the ionization section becomes a molecular state and is ionized by corona discharge generated by the needle 5. However, the ratio of the number of sample molecules to the number of mobile phase molecules in the ionization section is 10 ⁴
There is an order of magnitude of 1010 ^5, and therefore ionization by corona discharge is performed first by mobile phase molecules. But,
It is also true that the sample molecules are slightly ionized directly by corona discharge. Thereafter, the mobile phase molecular ions collide with the sample molecules, protons are transferred from the mobile phase molecular ions to the sample molecules by a proton transfer reaction, and sample molecular ions of M + ¹ (molecular ions to which one proton is added) are generated. . In the above process, the negative ion generates a sample molecular ion of M ⁻¹ (molecular ion from which one proton has been removed) due to proton elimination or resonance absorption. In the case of the API method, M- ¹ is particularly well observed. This reaction has a high reaction rate and is one of the important reactions in chemical ionization. In particular, in the case of the API method, since the pressure of the ion part is under atmospheric pressure, collisions between the mobile phase molecular ions and the sample molecules are reliably performed in a short time, and particularly, the sample is in the order of 10 ^-12 g and 10 ^-9 g. In the measurement, all the sample molecules are ionized, so that the sample molecule ions can be measured with high sensitivity.

As described above, in the case of the API method, positive and negative ions are generated by a molecular reaction. Therefore, when negative ions are measured, the voltage applied to the needle 5 causes corona discharge similarly to positive ion measurement. It was considered possible to measure by applying a voltage. However, when actually performing the measurement, when a positive voltage is applied to the needle 5, the negative ions are attracted to the needle portion and cannot pass through the first pore electrode 6, and are detected by the analysis portion. Proved impossible.

Therefore, when measuring negative ions, the ion accelerating voltage is applied to the second pore electrode 7 from the negative ion accelerating power supply 14 by turning the switching relay 12 OFF and the switching relay 13 ON. When the switching relay 15 is turned off and the switching relay 16 is turned on, a voltage that satisfies “first pore electrode voltage <second pore electrode voltage” is applied to the drift voltage. The voltage applied to the needle 5 is controlled by the switching relay 17
When the switching relay 18 is turned off and turned on, a negative high voltage is applied from the negative needle high voltage power supply 19. These switchings are all performed synchronously, and the switching signal is output from the positive / negative ion measurement switching device 21 or the computer of the data processing device 20. From this, the negative ions are converted into the first fine electrode 6 and the second fine electrode 7 similarly to the positive ion measurement.
And negative ions can be measured with high sensitivity.

Also, when measuring positive ions, use the switching relay described above.
It goes without saying that ON and OFF all operate in the opposite manner, and the voltage applied to each electrode satisfies the positive ion measurement state.

〔The invention's effect〕

As described above, in the present invention, a liquid containing a sample is stabilized in a mist state, guided to a needle electrode, and ionized into positive ions or negative ions by the needle electrode. Then, regardless of whether the needle-like electrode generates positive ions or negative ions, the ions can be accelerated in the intermediate pressure region and collide with neutral molecules to cleave cluster ions.
Thus, stable and highly accurate mass spectrometry can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an LC / API mass spectrometer, and FIG. 2 is a diagram showing details. 1 ... liquid chromatograph, 2 ... Teflon pipe, 3
... atomization unit, 4 ... ionization chamber, 5 ... needle electrode, 6 ...
First pore electrode, 7 Second pore electrode, 8 Mass spectrometer, 9 Ion acceleration power supply, 10 Positive ion drift power supply, 11 Positive ion needle electrode power supply, 12 Positive Ion acceleration power supply connection relay, 13 ... Negative ion acceleration power supply connection relay, 14
… Negative ion acceleration power supply, 15… Positive ion drift power supply connection relay, 16… Negative ion drift power supply connection relay, 17
…… Positive ion needle electrode power connection relay, 18 …… Negative ion needle electrode power connection relay, 19 …… Negative ion needle electrode power supply,
20 Data processing device, 21 Positive / negative ion measurement switching device, 22 Negative ion drift power supply.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ identification symbol FI H01J 49/04 H01J 49/04 (58) Investigated field (Int.Cl. ⁶ , DB name) H01J 49/00-49/48 G01N 27/62

Claims (6)

(57) [Claims] In an atmospheric pressure ionization mass spectrometer having an intermediate pressure chamber having a pressure lower than the atmospheric pressure, a mass analysis chamber having a pressure lower than the intermediate pressure chamber, and a needle electrode, a liquid containing a sample is atomized. Atomizing means for generating atomized fog, discharging the needle-shaped electrode under substantially atmospheric pressure to ionize a sample contained in the fog, and analyzing the ionized sample through the intermediate pressure through the mass spectrometry. Means for conducting mass spectrometry by introducing the positive and negative voltages to the needle-shaped electrode, and a first means arranged so as to face at least a part of the intermediate pressure chamber. An electrode and a second electrode, wherein the first electrode is disposed closer to the needle electrode than the second electrode, and the first electrode is lower than the second electrode or the first electrode is the second electrode. Means for supplying voltage so that it is higher than the electrode The first electrode has a lower voltage than the second electrode when the needle electrode has a negative voltage, and the first electrode has a lower voltage when the needle electrode has a positive voltage. An atmospheric pressure ionization mass spectrometer, wherein the voltage is higher than that of the second electrode. 2. The atmospheric pressure ionization mass spectrometer according to claim 1, wherein said liquid is supplied from a liquid chromatograph. 3. The atmospheric pressure ionization mass spectrometer according to claim 1, wherein the switching of the polarity of the needle-like electrode and the switching of the voltage of the first electrode and the voltage of the second electrode are synchronized. Total. 4. The method according to claim 1, wherein the intermediate pressure chamber is 1 Torr.
An atmospheric pressure ionization mass spectrometer characterized by a pressure of r to 0.1 Torr. 5. The device according to claim 1, further comprising a first partition separating the intermediate pressure chamber from the atmosphere, and a second partition separating the intermediate pressure chamber and the mass spectrometry chamber, wherein the first electrode is connected to the first electrode. 1
An atmospheric pressure ionization mass spectrometer provided on a partition wall, wherein the second electrode is provided on the second partition wall. 6. The method according to claim 5, wherein the first electrode and the second electrode are fine pore electrodes, and the ionized sample is led to the mass spectrometry chamber via these fine pore electrodes. Atmospheric pressure ionization mass spectrometer.