JP2707104B2 - Mass spectrometry method and mass spectrometer - Google Patents

Description

The present invention relates to a mass spectrometer (LC / M) directly connected to a liquid chromatograph.
More particularly, the present invention relates to a mass spectrometer and a mass spectrometer suitable for stable ionization without causing discharge when measuring negative ions in EHD (Electro Hydro Dynamic) ionization.

[Conventional technology]

It is generally difficult to stably vaporize molecules dissociated as ions in a liquid, and vaporization of ions by electric repulsion is the most energetically advantageous method. There is an EHD ionization method as an ionization method based on this principle.

The advantage of this method is that a strong electric field is necessary for ionization, but no additional energy such as heating is required. Therefore, ionization without thermal decomposition can be achieved. By changing the direction of the electric field, positive or negative ions can be extracted more selectively from the solution.

In general, a liquid having a flow rate of several tens of μ / min or less is passed through a conductive thin tube as shown in FIG. 3, and a counter electrode is provided so as to face the thin tube. When a voltage of about 2 to 3 kV is applied between the thin tube and the counter electrode, the liquid at the tip of the thin tube is pulled by an electric field to have a conical shape. When the electric field exceeds a certain threshold, charged microdroplets are sprayed. To extract positive ions, a high positive voltage is applied to the thin tube. To extract negative ions, a high negative voltage is applied to the thin tube.

At this time, not only negative ions are extracted from the liquid front end, but also electrons are also extracted. When a large amount of electrons are emitted, the threshold value of discharge breakdown is exceeded and corona discharge starts. When the corona discharge starts, a large amount of ions are generated from the discharge, and secondary ionization such as an ion molecule reaction is also performed. Therefore, the ionic species originally present in the eluent cannot be determined. Therefore, when measuring negative ions, as shown in FIG. 4, the periphery of the EHD ionization tubule is surrounded by a flow of molecules containing elements having a high electronegativity such as oxygen and freon, and the generated electrons have a high electronegativity. Absorb by element. When the discharge is started, the discharge current sharply increases as shown in FIG.
As shown in FIG. 3, a high resistance is inserted on the high voltage supply line,
A method utilizing the fact that the supply voltage decreases when the discharge is started has been used.

[Problems to be solved by the invention]

However, when this ionization is used for LC / MS, the kind and concentration of the component of the sample flowing in constantly change, so that there is a problem that stable ionization that does not cause discharge cannot be expected in the above-mentioned measures.

An object of the present invention is to provide a mass spectrometry method and a mass spectrometer capable of performing stable ionization even for a system that variously changes in components and concentrations flowing into the system.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a mass spectrometer that continuously introduces a liquid through a capillary and applies a high positive or negative voltage to a counter electrode to the capillary to generate positive or negative ions. In the method, a magnetic field is provided on an extension of the thin tube, and the magnetic field selectively detects electrons generated together with the negative ions when a high negative voltage is applied to the thin tube, and according to the amount of electricity of the electrons, It is characterized in that the voltage applied to the thin tube is controlled.

In a mass spectrometer that continuously introduces a liquid through a thin tube and applies a positive or negative high voltage to the counter electrode to the counter electrode to generate positive or negative ions, a magnetic field is generated on an extension of the thin tube. Provided by the magnetic field, to select electrons generated together with the negative ions when a high negative voltage is applied to the thin tube, comprising an electron detector for detecting the amount of electricity of the electrons, according to the amount of electricity The method is characterized in that a voltage applied to the thin tube is controlled.

[Action]

According to the above configuration, the liquid is continuously introduced into the thin tube,
The electrons generated together with the negative ions when a high negative voltage is applied to the thin tube have a smaller mass than the negative ions, so that they can be selectively deflected by the magnetic field. By controlling the applied voltage, rapid generation of electrons can be prevented, corona discharge can be prevented, and stable negative ions can be obtained.

〔Example〕

Hereinafter, an embodiment of the mass spectrometer according to the present invention will be described with reference to FIG.

The eluent stored in the eluent storage tank 1 is sent to the sample inlet and the column 5 via the pump 2 and the damper 3. A sample is injected from a sample injection port 4 and separated into components in a column 5 and sent to a conductive thin tube 7 via a tube 6 made of Teflon or the like. A counter electrode 9 is provided to face the thin tube 7, and a voltage of 2 to 3 kV is applied between the two.
When a negative high voltage is applied to the thin tube 7, negative ions (shown in the figure) and electrons (shown in the figure) are discharged together with negatively charged fine droplets from the conical liquid at the tip of the thin tube 7. A weak magnetic field 8 is generated in a direction perpendicular to the direction in which the charged particles are emitted. The strength of the magnetic field 8 is about several tens to 50 gauss, and electrons and ions can be easily distinguished. That is, electrons are easily deflected while ions are hardly deflected. Electrons are detected by an electron detector 10 and amplified by a DC amplifier 11, thereby controlling a high voltage power supply 12.

FIG. 2 shows the relationship between the voltage E and the current I obtained when the liquid flows out of a thin tube provided perpendicular to the counter electrode and a high voltage is applied between the counter electrode and the thin tube. As the voltage is increased, ions are extracted from the liquid tip from a certain value. When the voltage is further increased, electrons are rapidly emitted from the liquid tip, corona discharge is started, and the discharge current is rapidly increased. Therefore, if electrons emitted from the liquid tip can be detected, it is possible to control the applied voltage to prevent corona discharge.

However, since the charged particles emitted from the liquid front include negative ions in addition to electrons, control cannot be performed unless these two are detected separately. The distinction between electrons and negative ions can be easily made by providing a weak magnetic field (several tens of gauss) on the axis from which the charged particles are emitted and deflecting and detecting only the electrons. The other negative ions have a mass of 1.84 × 10 ³ m times that of the electrons when the mass is m, so that it can be considered that the negative ions are not substantially deflected by a magnetic field of about several tens of gauss.

〔The invention's effect〕

According to the present invention, in EHD ionization, the applied voltage can be controlled, so that negative ions can be stably detected without causing discharge.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an embodiment of the mass spectrometer of the present invention, FIG. 2 is a correlation diagram of applied voltage and current value, FIG. 3 is a schematic explanatory view showing a conventional example, and FIG. FIG. 10 is a schematic explanatory view of another conventional example for flowing freon and freon. 1 ... Eluent storage tank, 2 ... Pump, 3 ... Damper, 4 ...
... sample inlet, 5 ... column, 6 ... teflon tube, 7 ... conductive thin tube, 8 ... magnetic field, 9 ... counter electrode,
10 ... Electronic detector, 11 ... DC amplifier, 12 ... High voltage power supply.

Claims (3)

(57) [Claims] 1. A mass spectrometry method for continuously introducing a liquid through a thin tube and applying a high positive or negative voltage to the counter electrode to the counter electrode to generate positive or negative ions. A magnetic field is provided on the line, and the magnetic field is used to selectively detect electrons generated together with the negative ions when a high negative voltage is applied to the capillary, and control the voltage applied to the capillary according to the amount of electricity of the electrons. Mass spectrometry method characterized by performing. 2. A mass spectrometer which continuously introduces a liquid through a capillary and applies a positive or negative high voltage to the counter electrode to generate a positive or negative ion. A magnetic field is provided on the line, and the magnetic field includes an electron detector for selecting electrons generated together with the negative ions when a high negative voltage is applied to the thin tube, and detecting an electric quantity of the electrons. A mass spectrometer characterized in that a voltage applied to the thin tube is controlled in accordance with the following. 3. The mass spectrometer according to claim 2, wherein said magnetic field is provided by a permanent magnet.