JPH0518845Y2 - - 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 heated to, for example, 10 ^-4 Torr by the first oil diffusion pump 15.
a rear chamber 17 containing a mass filter (e.g. quadrupole mass filter) 16;
For example, the inside is 10 ^-5 by the second oil diffusion pump 18.
Being attracted to Torr. In this state, when electrons or ions are planted in the argon gas near the high frequency magnetic field, 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 the nozzle 8 and the skimmer 9, and then enter the small disk 14a and the ion lenses 14b, 14.
After converging through the mass filter 16
is guided to the secondary electron multiplier 19 and detected,
The detection signal is sent to the signal processing section 20 for calculation and processing.
Through the processing, the analysis value of the element to be measured in the sample is obtained.

<Problems to be solved by the invention> However, in the above conventional example, argon plasma is used as the high frequency inductively coupled plasma, and the mass spectrum drawn on a recorder etc. according to the output of the mass spectrometer detection section is Ions of argon-related molecules such as ArO ⁺ ions and Ar ₂ ⁺ ions began to appear. Also, since the mass numbers of ArO ⁺ ions and Ar ₂ ⁺ ions are 80 and 56, respectively, the peak of ArO ⁺ ions has a mass number of 80 and 56, respectively.
and 56, which overlapped with the peaks of Se ⁺ ions and Fe ⁺ ions, respectively, causing spectral interference. Therefore, Se and Fe (or direct
Analyzes using elements to be measured such as Ca and K ⁺ which overlap with Ar ⁺ ions and ArH ⁺ ions have become difficult or even impossible.

The present invention was devised in view of the shortcomings of the conventional examples, and its purpose is to reduce or eliminate the influence of argon-related molecular ions and to provide high-frequency inductive coupling that makes it possible to easily and accurately measure the elements to be measured. The purpose of the present invention is to provide a plasma mass spectrometer.

<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; The nitrogen gas is gradually replaced by nitrogen gas supplied through two flow rate control valves and a fluid mixing section, and the nitrogen gas is supplied within a high frequency power source that supplies a high frequency current to a high frequency induction coil wound around the plasma torch. The reason is that it is configured so that impedance matching is performed in response to replacement.

<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 23c are first and second flowmeters, 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 closes gradually (that is, the discharge pressure gradually decreases to zero). outermost chamber 1c of plasma torch 1,
To the outer chamber 1b and the inner chamber 1a, from the argon gas supply source 3, the first pressure reducing valve 22a → the first flow meter 23a →
The amount of argon gas supplied through the first flow rate control valve 24a → fluid mixing part 25 gradually decreases, and the amount of argon gas supplied from the nitrogen gas supply source 21 → second pressure reducing valve 22b → second flow meter 23b → second flow rate control valve The amount of nitrogen gas supplied through 24b will gradually increase. During this time, a matching circuit (not shown) in the high frequency power supply 10 is adjusted to match the impedance. In this way, finally, the outermost chamber 1c, the outer chamber 1b, and the inner chamber 1a of the plasma torch 1 have the following:
The amount of argon gas supplied from the argon gas supply source 3 through the first pressure reducing valve 22a → first flowmeter 23a → first flow rate regulating valve 24a → fluid mixing section 25 becomes zero, and the amount of argon gas supplied from the nitrogen gas supply source 21 through 2 pressure reducing valve 2
2b → second flow meter 23b → second flow control valve 24b
Only nitrogen gas is supplied through the
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 spectral diagram drawn by guiding the output signal of the signal processing section 21 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 ArO ⁺ ions and
Ions of argon-related molecules such as Ar ₂ ⁺ ions have disappeared, creating a good background condition for measuring atoms with a mass number of 28 (ie, N ₂ ) or more. Therefore, spectral interference does not occur even for Se ⁺ ions and Fe ⁺ ions, which have the same mass numbers as ArO ⁺ ions and Ar ₂ ⁺ ions, respectively, and Se and Fe (or
Analyzes using elements to be measured such as Ca and K) can also be performed accurately. Note that the present invention is not limited to the above-mentioned embodiments, and can be modified in various ways. For example, air may be gradually introduced into the outermost chamber 1c, outer chamber 1b, and inner chamber 1c of the plasma torch 1 shown in FIG. It is permitted to supply the same.

<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
Since the structure is such that nitrogen gas is gradually supplied in place of the argon gas supplied to the inner chamber 1a, the influence of argon-related molecular ions is reduced or eliminated, and the element to be measured can be easily and accurately measured. A high-frequency inductively coupled plasma mass spectrometer has been 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. Argon gas supplied through the mixing section is supplied from a nitrogen gas supply source to a second pressure reducing valve, a second flow meter, a second flow control valve,
and is configured to be gradually replaced by nitrogen gas supplied through the fluid mixing section, and
A high-frequency inductively coupled plasma mass spectrometer, characterized in that the high-frequency inductively coupled plasma mass spectrometer is configured such that impedance matching is performed in correspondence with the replacement within a high-frequency power source that supplies high-frequency current to a high-frequency induction coil wound around the plasma torch. (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.