JPH01137553A - Mass spectrometer - Google Patents

Abstract

PURPOSE:To make a mass spectrometer small-sized and reduce the cost by switching it to a mode superimposedly applying the DC voltage and the RF voltage to a quadruple-electrode section and a mode applying only the RF voltage. CONSTITUTION:A measurement mode scanning only the RF voltage can be switched in addition to the normal measurement mode applying the voltage superimposed with the DC voltage and the RF voltage to a quadruple-electrode section and scanning the voltage while the Vdc/Vrf ratio is kept constant to measure the mass spectrum. The measurement with no reduction of the ion permeation efficiency can be performed, and high-mass ions generated by an FAB ion source are efficiently measured. The mass spectrometry on a nonvolatile or thermally unstable sample with the FAB ion source can be thereby performed with a small-sized and inexpensive quadruple-electrode type mass spectrometer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a mass spectrometer that targets thermally unstable compounds and poorly volatile compounds.

[Prior Art] Gas chromatograph mass spectrometers (GCMS) are used for the separation and analysis of complex mixture samples, but in principle they are limited to volatile samples. Many biological components are thermally unstable or poorly volatile, making analysis difficult with GCMS. In order to enable mass spectrometry targeting these, various ionization methods have been developed and used as additional functions of GCMS. Fast neutral atomic bombardment
Atom bombardment (FAB) ion sources were also developed for this purpose and are now in practical use.

[Problems to be solved by the invention] Quadruple seed mass spectrometers are being used more and more because they are smaller and cheaper than conventional magnetic field sector mass spectrometers, but the biggest problem is that As the ion transmission efficiency increases, the ion transmission efficiency decreases, and the measurement mass range is limited compared to the magnetic field sector type. Therefore, at present, FAB ion sources are also used in combination with magnetic field sectors. In other words, if a large molecule is to be analyzed using the FAB ionization method, a large and expensive magnetic field sector type device must be used.

In view of the above background, an object of the present invention is to provide a compact, low-cost mass spectrometer that exhibits sufficient practical performance by combining an FAB ion source and a quadrupole mass spectrometer.

[Means for solving the problem] In quadrupole mass spectrometers, direct current (d
c) A mass spectrum is measured by applying a voltage that is a superimposed voltage and a radio frequency (RF) voltage, and scanning the voltage while keeping the ratio of both (Vdc/Vrf ratio) constant. A feature of the present invention is that in addition to this normal measurement mode, switching to a measurement mode that scans only high-frequency voltage enables measurement without deterioration of ion transmission efficiency. The method of configuring the device enables efficient measurement of ions.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5.

First, FIG. 1 is a characteristic diagram relating to the operating principle of a quadrupole mass spectrometer, and is generally called a stability diagram. Ions incident along the central axis of the quadrupole electrode travel in the axial direction while vibrating due to the high-frequency electric field, but only ions that satisfy certain conditions become stable vibrations, pass through the quadrupole part, and are detected by the detector. reach. Other ions become unstable vibrations and collide with the electrodes on the way and are lost. The shaded area in the figure corresponds to the area that satisfies the stable vibration conditions. a/q=- in the figure
A constant straight line is called an operating line, and when the voltage is scanned while keeping the ratio of Vdc/Vrf constant, a+Q moves on this operating line, and only while this straight line is in the stable region, the quality ff
1M ions are detected. In this case, Vrf:
High frequency voltage (V), r: Radius of inscribed circle of quadrupole electrode (m), f: Frequency (H2) r is a constant determined by the device, and if f is constant, M is proportional to Vrf, so , mass spectra can be measured by this voltage scanning. The above is the normal measurement mode of the quadrupole mass spectrometer, and the bandpass buoy 11 for ion mass
Work as a night. On the other hand, in voltage scanning using only high-frequency voltage, which is the main point of the present invention, it functions as a bypass filter, and its critical mass is given by the following equation.

Mcutoff=0.77 ・M Figure 2 shows its characteristics. Ions with a mass number greater than Mcutoff pass through the quadrupole electrode section and are detected, so the higher the mass in normal mode, the higher the Phenomenon where transmission efficiency decreases, so-called mass-d 1scr 11n
ion is not a problem, and even high-mass ions can be detected efficiently. Figure 3 shows the detected ion signal when only the high-frequency voltage is scanned. The change in the ion signal with respect to M is shown in (a) of the figure ), resulting in a step-like response, a so-called integral curve.

(b) in the figure is a differential curve obtained by a differential circuit,
Corresponds to the mass spectrum ζ.

Next, FIG. 4 shows the configuration of an apparatus according to an embodiment of the present invention. 1 is a fast neutral atom ion source, and a measurement sample is introduced into the ion source from a direct sample introduction section 8. FIG. 5 shows a schematic structural diagram of the ion source section. 11 is a fast neutral atom beam gun. Normally, xenon ions are generated using an ion gun using xenon gas, and when this ion beam is introduced into a gas chamber containing the same type of gas, a high-speed xenon atomic beam generated by a charge exchange reaction is made to strike the target coated with the sample. It ionizes the sample. Reference numeral 12 designates an ordinary electron striking ion source, and reference numeral 13 designates an ion lens section for converging the generated ion beam. A quadrupole electrode is provided to the right of the ion lens (not shown).

14 is a sample introduction probe, and a target is attached to its tip. The sample introduction probe is directly inserted using the sample introduction device 1. 2 in FIG. 4 is a quadrupole mass spectrometer, and 3 is an ion detector. 4 is an ion signal amplification measurement circuit and a differentiation circuit. Reference numeral 5 denotes a control section, which controls the evacuation system, heating control, mode switching, analysis condition control, etc. 6 is a direct current and high frequency voltage power supply section that applies to the quadrupole electrodes. 7 is a computer system that performs data processing and equipment operation. With this device configuration, mass spectrometry can be performed by arbitrarily switching between a normal mode in which both DC voltage and high-frequency voltage are scanned, and a mode in which only high-frequency voltage is scanned. Therefore, volatile samples are analyzed using a normal electron equilibrium ion source and a quadrupole mass spectrometer in normal mode, while non-volatile or thermally unstable samples are analyzed using an FA8 ion source. Introduction to quadrupole mass spectrometers such as the FAB ion source, which can perform analysis using a quadrupole mass spectrometer in a mode that scans only high-frequency voltage, which was previously difficult due to mass limitations of quadrupole mass spectrometers. Practically sufficient performance can also be obtained by combining them.

Although this embodiment describes an example of application to a mass spectrometer, it is of course easily applicable to a gas chromatograph mass spectrometer.

〔Effect of the invention〕

According to the present invention, mass spectrometry using a FAR ion source can be performed on non-volatile or thermally unstable samples using a small and inexpensive quadrupole mass spectrometer.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams explaining the principle of the present invention, FIG. 3 is a diagram explaining mass spectrum I# measurement according to the present invention, and FIGS. 4 and 5 are diagrams showing the configuration of an apparatus that is an embodiment of the present invention. ■,...FAB ion source, 2. ... Quadruple-like mass spectrometer, 3゜... Ion detector, 4. ...Ion signal measurement circuit section, 5. ...control unit, 6. ...High voltage power supply section,
7. ...Computer E/Sym, 8. ...Direct sample introduction section 11. ...high-speed neutral atomic gun, 12.・・・
- Electron bombardment ion source, 13. . . . ion focusing lens section 14, . . . sample introduction probe 13;

Claims (1)

[Claims] 1. In a quadrupole mass spectrometer equipped with a fast neutral bombardment ion source, switching between a mode in which DC voltage and high-frequency voltage are applied in a superimposed manner to the quadrupole section and a mode in which only high-frequency voltage is applied A mass spectrometer characterized by having a mechanism