JPH0770301B2 - Mass spectrometer - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a mass spectrometer, and more particularly to an improvement of a mass spectrometer having a mechanism for cleaving cluster ions generated by an ion-molecule reaction at high pressure. .

[Background of the Invention]

As a means for analyzing trace impurities in gas, a means for efficiently ionizing a sample under a pressure of several Torr to 1 atm and introducing the sample in the form of ions from the pores into the mass spectrometer for analysis has been developed and put into practical use. (Reference Analytical Chemistry, vol.45, No.6, May 197)
3, p.936-943; Analytical Chemistry (Analy
tical Chemistry), vol.45, No.6, May 1974, p.706-711.
(JP-A-51-7991). Compared with the conventional electron impact ionization method, this method produces ions in two steps: primary ionization by corona discharge at 1 atm or Niβ irradiation and subsequent secondary ionization by ion-molecule reaction. It has a high sensitivity of 3 to 6 digits, less decomposition of sample molecules, and a simple and easy-to-interpret spectrum can be obtained.

FIG. 1 shows an atmospheric pressure ionization mass spectrometer equipped with a corona discharge needle electrode as an ionization means, which is composed of an ionization section 1, an intermediate pressure section 2 and a mass analysis section 3 and is connected by a pair of reholes 4 and 5. .

In the figure, in the ionization section 1, primary ionization is performed by the corona discharge needle electrode 6 and secondary ionization is subsequently performed by the ion-molecule reaction, and the generated ions of the molecule to be measured pass through the pores 4 to the intermediate pressure section 2. To do. The intermediate pressure section 2 is maintained at about 1 Torr by the primary exhaust 7.

Then, after passing through the second pores 5 and entering the secondary-exhausted mass spectrometer 8, the mass was analyzed by the mass spectrometer and then detected by the detector 9. The intermediate pressure section 2 is provided with an ion focusing electrode 10 which gives a centripetal electric field so as to focus the ions on the second pores 5. Further, an ionizing means 11 for calibration is provided before the mass spectrometric section 3 and is an electron impact ion source in the figure.

Various gases such as nitrogen, air, oxygen, argon, or helium can be used for introducing the sample, but nitrogen gas is most widely used. Therefore, the case where nitrogen gas is used as a carrier will be described in detail below.

In the sample, primary ions are generated by the corona discharge tension electrode 6 in the ionization section 1 at atmospheric pressure. The primary ions are N ⁺ generated by ionization of nitrogen, which is the majority component, or
N ₂ ⁺ . They react immediately with nitrogen to N ₄ ⁺ and N ₃
Give ⁺ .

As shown in these reactions, oxygen and water, which exist as trace impurities in nitrogen, are directly ionized from N ₄ ⁺ . From molecules with low ionization potential and large molecules of proton affinity (M) to water cluster ions H
⁺ (H ₂ O) _n-1 H ⁺ · M is generated. The generated M-containing ions and H ⁺ (H ₂ O) _n are stable and do not change even when they collide with nitrogen. In this way, ions such as MH ⁺ and (H ₂ O) _n-1 H ⁺ · M are amplified with each collision, and many kinds of cluster ions are generated, which selectively ionize sample molecules. It The clusters thus generated at atmospheric pressure are introduced into the intermediate pressure portion (about 1 Torr) 2 through the first pores 4. When a voltage (hereinafter referred to as a drift voltage) applied to the pores 4 and 5 at both ends of the intermediate pressure portion 2 is applied, an electric field is generated, and the cluster starts drifting in the electric field direction. By this electric field, the ions can be efficiently converged to one point, and the electric field concentration of the ions is performed, but at the same time, the internal energy of the ions is excited. That is, the clusters are accelerated by the drift electric field and have kinetic energy and collide with neutral molecules that are the carrier gas. At this time, a part of the kinetic energy of the cluster is given to the internal energy such as vibration and rotation of the cluster, and a part is given to the neutral molecule. Excitation of such internal degrees of freedom is performed at each collision. If the number of collisions is sufficient, the clusters will eventually be dissociated from weak bond sites. Since the kinetic energy of ions can be controlled by changing the drift voltage, increasing the drift voltage causes dissociation to start sequentially from weak cluster bonds.

When the carrier gas is nitrogen, oxygen, argon, etc., most of the generated cluster ions have a drift voltage for dissociation that does not depend on the type of carrier gas. Also, the ratio of the pressure P in the intermediate pressure part 2 (collision chamber) to the electric field strength E (E / P)
When the drift voltage is standardized by, the dissociating voltage does not depend much on the length of the collision chamber. This means that the standardized electric field strength (E /
It shows that there is a strong correlation between P).

As described above, in the conventional example, when the supply amount of the carrier gas C and the trace amount of the sample X fluctuates, the pressure in the ionization section 1 fluctuates, and the primary ionization and the secondary ionization due to the subsequent ion-molecule reaction are not constant. Pressure fluctuation of the intermediate pressure part 2 occurs, and pressure P of the intermediate pressure part 2 (collision chamber)
And the electric field strength E ratio (E / P) makes it impossible to standardize the drift voltage, and the collision dissociation of cluster ions is not constant. Therefore, there is a fluctuation in the spectrum intensity obtained,
However, there is a drawback in that the same stable spectrum cannot be obtained.

[Object of the Invention]

Therefore, the object of the present invention is to eliminate the drawbacks of the conventional atmospheric pressure mass spectrometer as described above, to obtain the same spectrum and spectrum intensity stably, and to provide an atmospheric pressure mass spectrometer with improved analytical performance. It is in.

[Outline of Invention]

In order to achieve the above object, in the present invention, a gas flow rate control device is provided in a conduit for introducing the sample contained in the carrier gas into the ionization section, and the generation of cluster ions in the ionization section and the intermediate pressure section are performed. A pressure detector is installed in the intermediate pressure section to ensure stable collisional dissociation of the cluster ions, and the gas pressure in the intermediate pressure section is detected, so that the pressure in the intermediate pressure section becomes constant. It is characterized in that the gas supply flow rate is controlled.

Example of Invention

 Hereinafter, the present invention will be described with reference to an embodiment.

FIG. 2 is an atmospheric pressure ionization chamber volume analyzer equipped with a sample gas control device and a gas pressure detection device according to the present invention. Hereinafter, in FIG. 2, those having the same reference numerals as those in the first order represent the same things, and therefore their explanations are omitted here.

As shown in FIG. 2, sample 12 contained in carrier gas
Gas flow rate control device in the introduction line 13 for supplying the gas to the ionization section
14 is provided, and a gas pressure detector 15 is provided in the intermediate pressure section 2 connected to the ionization section 1 by the pores 4. Intermediate pressure part 2
Is an area for collisional excitation and dissociation of cluster ions in the atmospheric pressure ionization mass spectrometer.
If the pressure is not kept constant, the state of dissociation of cluster ions will change and the obtained spectrum will change. Therefore, in the atmospheric pressure ionization mass spectrometer, it is important to keep the pressure of the intermediate pressure section 2 constant. One factor that causes the pressure fluctuation in the intermediate pressure section 2 is the internal pressure fluctuation in the ionization section 1. The internal pressure fluctuation of the ionization part depends on the sample gas flow rate when the temperature is constant. Therefore, it is necessary to control the flow rate of the sample gas and make the pressure of the intermediate pressure section 2 constant.

In this embodiment, the pressure of the intermediate pressure section 2 is detected so that the pressure of the intermediate pressure section 2 is constant, the output voltage of the gas pressure detection control circuit 16 is compared by the comparison control circuit 18, and the difference is zero. The control valve 19 can be controlled so as to control the sample gas flow rate.

As described above, in this method, the pressure of the intermediate pressure portion 2 is kept constant, so that in this embodiment, a stable vector can be obtained and the measurement accuracy can be improved. The stop valve 20 provided in the ionization section 1 is a valve used when special gas or trace gas analysis is performed.

As described above, according to the above embodiment, the ionization in the ionization section 1, the ion-molecule reaction and the cluster in the intermediate pressure section 2
Collision and dissociation of ions are performed stably. Consequently, the spectrum intensity obtained does not change, and a stable spectrum with good reproducibility can be obtained.

〔The invention's effect〕

As described above, according to the present invention, it is possible to easily set measurement conditions, eliminate fluctuations in spectrum intensity due to fluctuations in sample gas flow rate, and obtain stable spectra with good reproducibility when measuring the same sample. As described above, not only the accuracy of mass spectrometry can be improved, but also automation which can simplify mass spectrometry can be achieved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an atmospheric pressure ionization mass spectrometer equipped with a corona discharge needle electrode as an ionization means, and FIG. 2 is an atmospheric pressure ionization mass equipped with a sample gas control device and a gas pressure detection device according to the present invention. It is sectional drawing which shows an analyzer. 1 ... Ionization part, 2 ... Intermediate pressure part (collision chamber), 3 ...
... Mass spectroscope, 4,5 ... pores, 6 ... corona discharge needle electrodes, 7 ... primary exhaust, 8 ... secondary exhaust, 9 ... detector, 10 ... ion focusing electrode , 12 …… sample, 13 …… gas introduction line, 14 …… gas flow controller, 15 …… gas pressure detector, 16 …… gas pressure detector control circuit, 17 …… gas flow detector, 18… … Proportional control circuit, 19… Control valve, 20… Stop valve.

Front Page Continuation (72) Inventor Yataro Kondo 2-3-3 Fujibashi, Ome City, Tokyo Inside Hitachi Tokyo Electronics Co., Ltd. (56) Reference JP-A-53-81289 (JP, A) JP-A-49-5090 (JP, A) JP-A-52-27693 (JP, A)

Claims (1)

[Claims] 1. An ionization unit for introducing a sample, a collision ion dissociation unit for cluster ions, an ion focusing unit, an intermediate pressure unit for differential evacuation, and a mass analysis unit for performing ion analysis. In the atmospheric pressure ionization mass spectrometer in which the ionization section and the intermediate pressure section and the intermediate pressure section and the mass analysis section are connected by a slit with a pore, a gas flow rate control device in the ionization section sample gas introduction pipe, an intermediate pressure section A mass spectrometer characterized in that a gas pressure detection device is provided in the gas pressure detection device, and the sample gas flow rate is controlled by a gas flow rate control device in accordance with the output of the gas pressure detection device to maintain the gas pressure substantially constant.