JPH03261062A - Plasma trace element mass spectrometer - Google Patents

Abstract

PURPOSE:To reduce the power consumption of a mass spectrometer and miniaturize the spectrometer and reduce the cost of the spectrometer by setting the degree of vacuum of a first actuation area to less than 1Torr. CONSTITUTION:Samples are introduced into atmospheric pressure plasma 10 generated in the area (I) of atmospheric pressure on a plasma generating system so that the samples are ionized. The sample ions are expanded and diffused in the area (II) of 1 to 10<-3>Torr via a plasma sampling system 70 and an ion beam composed of the sample ions, etc., is formed by an ion takeout system provided in the area (III) of 10<-4> to 10<-5>Torr and consisting of an ion takeout electrode 80 and an ion accelerating electrode 90, etc. The ion beam is transported via an ion transporting system 100 to a mass spectrometry system 110 provided in the area (IV) of 10<-6> to 10<-7>Torr and the samples are identified by an ion detecting system 120.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultratrace element mass spectrometer using plasma, and particularly to the degree of vacuum in the first differential region for reducing the detection limit.

(1) [Prior art] As for the typical conventional plasma-based ultratrace element mass spectrometer, the Spectrochemistry Acta
rochimica Acta) 40 B (198
5), pages 1525 to 1537.

FIG. 3 shows a schematic diagram of the main parts of the conventional device.

Here, 10 is atmospheric pressure plasma, 11 is plasma torch, 12 is high frequency coil, 20 is plasma sampling cone, 21 is sampling orifice (1, 5-upper,
30 is a schema, 31 is a schema orifice (1.5 to 0.7 mmφ), and 40 is an ion extraction electrode.

In this device, the atmospheric pressure (760 Torr) between the plasma torch 11 and the plasma sampling cone 2o is
), the atmospheric pressure plasma 10 is first generated by the high frequency power supplied to the high frequency coil 12. Next, the atmospheric pressure plasma 10 is transferred from the sampling orifice 21 to the plasma sampling cone 2o and the first differential area (1 to 3) of the area (2) between the schema 30
Torr). Further, through the schema orifice 31, the area (■) (~1O-4 Torr)
The expanded plasma is diffused and ions are extracted from the plasma by applying a voltage between the schema 30 and the ion extraction electrode 40. The ions are then introduced to a mass spectrometry system such as a mass filter through an ion transport system consisting of an ion lens, etc., and their masses are identified.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not give sufficient consideration to the loss (attenuation) of sample ions to be analyzed in the first differential region of the region (I[), and has a major problem with the detection limit and measurement sensitivity.

The present invention aims to solve the above-mentioned problems, and further aims to reduce the power consumption, size, and cost of the device.

[Means to solve the problem]

In order to achieve the above object distantly, the degree of vacuum in the first differential region (3) of region (II) should be changed from 3 to I Torr in the prior art to less than I Torr, more preferably, as shown in FIG. is 0.8 Torr or less.

[Effect]

The high vacuum of the first differential region acts to significantly reduce the loss (attenuation) of sample ions to be analyzed in the plasma expanding from the sampling cone, as shown in FIG. . In other words, the initial intensity of the sample ions is ■. , the pressure in the first differential region is P, the total collision cross section with residual gas molecules is σ, and the interaction (reaction) distance is α, then the intensity of the sample ion after reaction is I
cc I. There is a relationship exp(-a P Q),
Assuming that σ and Q are constant, the work increases exponentially as P decreases. Furthermore, as shown in FIG. 1, the background noise BN can also be significantly reduced. For this reason, the pressure in the first differential region is preferably kept below I Torr, particularly below 0.8 Torr. Note that when the collision becomes negligible at 10-3 Torr or less, these effects are small (4).Therefore, the capacity of the exhaust device in the region (m) can be reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 shows a change in ion intensity (of a sample to be analyzed, for example, Mg", Go"In+, etc.) with respect to the degree of vacuum P in the first differential region, which shows the effects of the present invention. Second
The figure shows the apparatus of the invention from which the data of FIG. 1 was obtained. Here, ■0 is atmospheric pressure plasma, 50 is a sample introduction system consisting of a nebulizer, etc., 60 is a plasma generation system consisting of a microwave cavity, plasma torch, etc., 70 is a plasma sampling system such as a plasma sampler, and 80 is an ion An extraction electrode, 90 an ion transport system consisting of ions, 110 a mass spectrometry system consisting of a mass filter, etc., 12
0 indicates an ion detection system consisting of a secondary electron multiplier (5) tube, etc. Also, ■1 to ■8
is a vacuum valve, RP, -RP3 is a rough evacuation system (achieved vacuum -10-3 Torr) consisting of a rotary pump, mechanical booster, etc., and D Pl and DP2 are high vacuum evacuation systems consisting of an oil diffusion pump, turbo molecular pump, etc. The system (achieved vacuum level 10-6 to 1 O-ll Torr) is shown.

Next, the operation of this device will be explained. First, the plasma generation system (using microwave, high frequency, DC power, etc.)
Atmospheric pressure plasma 10 generated in the atmospheric pressure region (1)
Introducing the sample (gas, liquid, solid, etc.) to be analyzed into (He, N2, Ar, etc.) and ionizing it (sample ion)
do. Next, the sample ions together with the atmospheric pressure plasma 10 are passed through a plasma sampling system 70 consisting of the plasma sampler at 1-10-3 Torr (I T
less than orr, more than 10''Torr) area (■) (
10-4 to 10-'T
ORR region (DI) (6) Forms an ion beam consisting of source ions.

Then, the ion beam is transmitted through the ion transport system 100 with an efficiency of <10-6 to 10-7 Torr (I
The sample to be transported to the mass spectrometry system 110 provided in V) and analyzed using the ion detection system 120 is identified. At this time, the region (TI) is RP, (pumping speed: ~100OQ/min), and the region (11) is RP2.
(Exhaust speed: -300Q 7m1n) and DP, (Exhaust speed knee 800Q/5CIC), area (TV) is R
P3 (-200Q/m, in) and DP.

(Evacuation speed: ~300Q/5ee), the above-mentioned degree of vacuum can be obtained, and the sample ions can be detected efficiently. Furthermore, since the background noise is reduced, the signal-to-noise ratio is increased, and the detection limit can be reduced by 1°.In addition, in the above, there are limitations other than the degree of vacuum (less than I Torr to more than 1 O-3 Torr). Instead, various plasma generation systems, sample introduction systems, ion extraction systems, etc. may be used.

According to the present invention, as shown in FIG.
When the temperature is increased from more than r to less than I Torr -0.8 Torr, the adiabatically expanded plasma expands into the region (II).
Attenuation due to interaction with residual gas can be significantly reduced, making it possible to increase the current (2) of the ions to be analyzed by more than 10 times (higher sensitivity). Furthermore, since the background noise BN can be reduced by more than twice, there is a great effect that the signal-to-noise ratio can be improved by more than 20 times, that is, the detection limit of analysis can be significantly reduced to 1/20 or less.

Furthermore, the degree of vacuum in the region (I[) is set to 0 and 8 Tor.
By setting it below r, the pumping speed of DPl and DP2 can also be reduced. In particular, the pumping speed of the DP has also increased from the conventional 2000 Q/sec to 600-1000 fi/s.
It has the effect of reducing ec. Therefore, there are significant effects such as reduction in power consumption and heat generation, miniaturization of the device, and cost reduction.

〔Effect of the invention〕

According to the present invention, a plasma trace element mass spectrometer with improved detection limits and measurement sensitivity can be obtained.

(8)

[Brief explanation of drawings]

FIG. 1 is a comparison diagram of the effects of the prior art and the present invention. FIG. 2 is a block diagram of one embodiment of the apparatus of the present invention, and FIG. 3 is a block diagram of the main parts of the prior art. DESCRIPTION OF SYMBOLS 10... Atmospheric pressure plasma, 20... Plasma sampling cone, 30... Schema, 40... Ion extraction electrode, 50... Sample introduction system, 60... Plasma generation system, 70... Plasma ion sampling system, 80... Ion extraction electrode, 90... Ion acceleration electrode, 100... Ion transport system, 110... Mass spectrometry system. (9)

Claims (1)

[Claims] 1. In a plasma trace element mass spectrometer comprising an atmospheric pressure plasma generation system, a sample introduction system, a plasma sampling system, an ion extraction system, an ion transport system, a mass spectrometry system, an ion detection system, and an exhaust system. . A plasma trace element mass spectrometer, characterized in that the degree of vacuum in the first differential region between the plasma sampling system and the ion extraction system is maintained at less than 1 Torr using the exhaust system. 2. The plasma trace element mass spectrometer according to item 1, wherein the degree of vacuum in the first differential region is 0.8 Torr or less.