JPH0518844Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a high frequency inductively coupled plasma mass spectrometer that reduces spectral interference due to argon-related molecular ions.

<Conventional technology> A high-frequency inductively coupled plasma mass spectrometer uses high-frequency inductively coupled plasma to excite a sample, and the generated ions are guided to a mass spectrometer through an interface consisting of a nozzle and a skimmer, where they are electrically detected. By precisely measuring the amount of ions, the element to be measured in the sample is analyzed with high precision. FIG. 2 is an explanatory diagram of the configuration of a conventional example of such a high frequency inductively coupled plasma mass spectrometer.
In this figure, argon gas is supplied from an argon gas supply source 3 to an outer chamber 1b and an outermost chamber 1c of a plasma torch 1 via a gas regulator 2, and an inner chamber 1
A sample in a sample tank 4 is atomized by a nebulizer 5, and then introduced by argon gas. Further, a high frequency current is passed through a high frequency induction coil 6 wound around the plasma torch 1 by a high frequency power source 10, and a high frequency magnetic field (not shown) is formed around the coil 6. On the other hand, the inside of the fore chamber 11 sandwiched between the nozzle 8 and the skimmer 9 is operated by a vacuum pump 12, for example.
It is attracted to 1Torr. Further, inside the center chamber 13, there is provided a small disk 14a for blocking light from entering on the center axis, and ion lenses 14b and 14c arranged at a constant distance from the small disk. The inside of the chamber 13 is suctioned to, for example, 10 ⁻⁴ torr. by the first oil diffusion pump 15 , and the inside of the rear chamber 17 accommodating a mass filter (for example, a quadrupole mass filter) 16 is sucked to a second oil diffusion pump 18 . For example, 10 ^-5 torr.
is attracted to. In this state, when electrons or ions are implanted in the argon gas near the high frequency magnetic field, a high frequency induced plasma 7 is instantaneously generated by the action of the high frequency magnetic field. The ions in the plasma 7 pass through a nozzle 8 and a skimmer 9, and then enter, for example, a small disk 14a and ion lenses 14b, 14.
c (or a double quadrupole lens), the electrons are converged, passed through a mass filter 16, and guided to a secondary electron multiplier tube 19 for detection, and the detection signal is sent to a signal processing section 20 for calculation and processing. By processing the sample, the analysis value of the element to be measured in the sample can be determined.

<Problems to be solved by the invention> However, in the above embodiment, argon plasma is used as the high frequency inductively coupled plasma, and the mass drawn on the recorder etc. according to the output of the mass spectrometer detection section is ArO ⁺ in the spectrum
ions and ions of argon-related molecules such as Ar ₂ ⁺ ions began to appear. Also, since the mass numbers of ArO ⁺ ion and Ar ₂ ⁺ ion are 80 and 56, respectively, the peak of ArO ⁺ ion has a mass number of 80 and 56, respectively.
Spectral interference began to occur, such as overlapping with the peaks of Se ⁺ ions and Fe ⁺ ions at 80 and 56, respectively. For this reason, analysis using Se ⁺ and the like as an element to be measured has become difficult or completely impossible. On the other hand, simply replacing the argon gas with nitrogen gas and creating a so-called _N2 plasma will widen the range of impedance matching within the high-frequency power source that supplies high-frequency current to the high-frequency induction coil wound around the plasma torch. Another drawback is that the current (or supplied power) must be increased, resulting in an increase in the manufacturing cost of the high-frequency inductively coupled plasma mass spectrometer.

The present invention was devised in view of the shortcomings of the conventional examples, and its purpose is to reduce the influence of argon-related molecular ions and to easily and accurately measure the elements to be measured using high-frequency inductively coupled plasma mass. Our goal is to provide analyzers.

<Means for Solving the Problems> The feature of the present invention that solves the above-mentioned problems is that, in a high frequency inductively coupled plasma mass spectrometer, argon is injected into a triple tube structure plasma torch that generates high frequency inductively coupled plasma. Argon gas is supplied from a gas supply source through a first pressure reducing valve, a first flow meter, a first flow control valve, and a fluid mixing section, and a nitrogen gas supply is supplied from a nitrogen gas source through a first pressure reducing valve, a first flow meter, a first flow rate regulating valve, and a second flow meter. The nitrogen gas supplied through the two flow control valves and the fluid mixing section is configured to be mixed at a constant mixing ratio and supplied.

<Example> Hereinafter, the present invention will be described in detail using figures. FIG. 1 is an explanatory diagram of the main structure of an embodiment of the present invention. In the figure, the same symbols as in FIG. 2 are used with the same meanings, and redundant explanation will be omitted here. Also, 2
1 is a nitrogen gas supply source, 22a and 22b are first and second pressure reducing valves, 23a and 23b are first and second flow meters, 24a and 24b are first and second flow rate regulating valves,
25 is a fluid mixing section.

In the embodiment of the present invention having such a configuration, first, the first pressure reducing valve 22a is opened (that is, the discharge pressure becomes a constant set pressure) and the second pressure reducing valve 22b is opened.
is closed (that is, the discharge pressure becomes zero). Further, the first and second flowmeters 23a and 23b are each set to a constant flow rate. In this state, argon gas is supplied to the inner chamber 1a of the plasma torch 1 from the argon gas supply source 3.
→It is supplied together with the atomized sample through the nebulizer 5. In addition, in the outer chamber 1b and the outermost chamber 1c,
Argon gas is supplied from the argon gas supply source 3 to the first
The fluid is supplied through the pressure reducing valve 22a, the first flow meter 23a, the first flow control valve 24a, and the fluid mixing section 25. In this state, high frequency energy is supplied from the high frequency power supply 10 to the high frequency induction coil 6, a high frequency magnetic field (not shown) is formed around the coil 6, and plasma 7 is generated by the action of the magnetic field. The ions in the plasma 7 are extracted into the center chamber 15 through the nozzle 11 and the skimmer 12, and then detected by the pole element 17. The detection signal is amplified by the secondary electron multiplier tube 20 and then sent to the signal processing section 21, where it is subjected to predetermined signal processing, and then a mass spectrum is drawn on a recorder (not shown) to record the analysis value of the sample. Start giving.

By the way, after the plasma using argon as described above is generated, the second pressure reducing valve 22b is gradually opened (that is, the discharge pressure gradually reaches a certain set pressure), and the first pressure reducing valve 22a is opened. It is gradually closed so that the discharge pressure of the first pressure reducing valve 22a reaches a constant set pressure. For this reason,
The outermost chamber 1c, the outer chamber 1b, and the inner chamber 1a of the plasma torch 1 are connected to the argon gas supply source 3 through a first pressure reducing valve 22a, a first flow meter 23a, a first flow control valve 24a, and a fluid mixing section 25. The amount of argon gas supplied through the nitrogen gas source 2 gradually decreases.
1, the amount of nitrogen gas supplied through the second pressure reducing valve 22b → second flow meter 23b → second flow rate regulating valve 24b gradually increases, and eventually the argon gas and nitrogen gas become constant. It will be supplied in a mixed state at a mixing ratio of . Thereafter, a matching circuit (not shown) within the high frequency power supply 10 is adjusted to achieve impedance matching. FIG. 4 is a spectrum diagram drawn by guiding the output signal of the signal processing section 21 to a recorder or the like (not shown) in such a state. Further, FIG. 3 is a spectrum diagram drawn by guiding the output signal of the signal processing section 20 to a recorder or the like (not shown) in the state of the conventional example described in detail using FIG. 2. As is clear from comparing Figures 3 and 4, in Figure 4 Ar ⁺ ions, ArO ⁺ ions,
The peaks of argon-related ions such as ArO ⁺ ions and Ar ₂ ⁺ ions are reduced, especially when compared with ArO ⁺ ions.
The peak of Ar ₂ ⁺ ions has decreased significantly and is in a good background state. Therefore, ArO ⁺
Se ⁺ with the same mass number as the ion and Ar ₂ ⁺ ion, respectively
Spectral interference does not occur for ions and Fe ⁺ ions, and analysis using Se, Fe, etc. as the measured elements can be performed accurately. Note that the present invention is not limited to the above-described embodiments, and can be modified in various ways. For example, a matching box may be provided separately from the high-frequency power source, and the impedance matching as described above may be performed using the matching box. Make it good. Further, a mechanism for gradually supplying nitrogen gas to the outermost chamber 1c of the plasma torch 1 shown in FIG. 1 may also be provided for the outer chamber 1b and the inner chamber 1c.

<Effects of the invention> According to the embodiment of the invention as described in detail above, the outermost chamber 1c and the outer chamber 1 of the plasma torch 1
In place of the argon gas supplied to the inner chamber 1a, nitrogen gas is gradually supplied to maintain a constant mixing ratio, reducing the influence of argon-related ions and making it easier to measure the elements to be measured. A high-frequency inductively coupled plasma mass spectrometer that enables quick and accurate measurements will be realized.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of an embodiment of the present invention, FIG. 2 is an explanatory diagram of the configuration of a conventional example, and FIGS. 3 and 4 are spectrum diagrams. DESCRIPTION OF SYMBOLS 1... Plasma torch, 3... Argon gas supply source, 7... High frequency inductively coupled plasma, 8... Nozzle, 9... Skimmer, 11... Foa chamber, 13... Center chamber, 16... Mass filter, 17 ... Rear chamber, 20 ... Signal processing section, 21 ... Nitrogen gas supply source, 22a, 2
2b...Pressure reducing valve, 23a, 23b...Flow meter, 2
4a, 24b...flow control valve, 25...fluid mixing section.

Claims (1)

[Claims for Utility Model Registration] (1) Ions produced by exciting a sample using high-frequency inductively coupled plasma are introduced into a vacuum, guided to a mass spectrometer detector through an ion optical system, and detected. In the analyzer for analyzing elements to be measured, a plasma torch having a triple tube structure that generates the high-frequency inductively coupled plasma is connected from an argon gas supply source to a first pressure reducing valve, a first flow meter, a first flow rate regulating valve, and a fluid. A second pressure reducing valve, a second flow meter, a second flow control valve, from the argon gas and nitrogen gas supply sources supplied through the mixing section
A high frequency inductively coupled plasma mass spectrometer, characterized in that the high frequency inductively coupled plasma mass spectrometer is configured such that nitrogen gas and nitrogen gas supplied through a fluid mixing section are mixed at a constant mixing ratio. (2) The plasma torch has a first
- A high-frequency inductively coupled plasma mass spectrometer according to claim 1, which is a plasma torch having a triple tube structure having an outermost chamber, an outer chamber, and an inner chamber through which a third compressed gas is introduced.