JPH0412448A - High-frequency induction-coupled plasma mass spectrometer - Google Patents

Abstract

PURPOSE:To facilitate the tuning of an ion lens and increase the permeability of an ion beam by providing an ion optical system constituted of two sets of parallel concave lens systems having displaced optical axes and applied with the preset symmetrical voltage. CONSTITUTION:The first parallel concave lens is formed with parallel concave lenses 24a, 24b, and the second parallel concave lens is formed with parallel concave lenses 24c, 24d. The first and second parallel concave lenses are located between an inlet aperture plate 21 and an outlet aperture plate 22, and openings 21', 22' of both aperture plates 21, 22 are off-centered each other. Symmetrical voltage 25a-25d centering on the average potential are applied to two sets of parallel concave lenses. The diverging action of ions is eliminated, the ion convergence effect in an ion lens system is increased, and the detection sensitivity is improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a high frequency inductively coupled plasma mass spectrometer,
More specifically, the present invention relates to a high frequency inductively coupled plasma mass spectrometer with an improved ion lens system.

<Prior art> A high frequency inductively coupled plasma mass spectrometer uses high frequency inductively coupled plasma to excite sample t1, and the generated ions are passed through an interface consisting of a nozzle and a skimmer into sample t1.
It is configured to analyze the element to be measured in the sample with high precision by guiding it to an analyzer and electrically detecting it to precisely determine the amount of the ions. FIG. 3 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 via a gas regulator 2 to the outer tube 1b and the outermost tube 1c of the plasma torch 1 installed in the matching box 1-, and to the inner tube 1a. The sample in the sample tank 4 is atomized by a nebulizer 5 and then carried in using 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 pressure inside the forechamber 11 sandwiched between the nozzle 8 and the skimmer 9 is reduced to, for example, ITorr by a vacuum pump 12.

In addition, an ion lens system 14 is provided in the center chamber 13.
is provided, and the interior of the center chamber 13 is heated to, for example, 10-'Tor by the first oil diffusion pump 15.
r.

The pressure in the rear chamber 17 housing the mass filter (for example, quadrupole mass filter) 16 is reduced to, for example, 10-' Torr by the second oil diffusion pump 18. When electrons or ions are planted in the argon gas in the vicinity of the high frequency magnetic field in this state, high frequency inductively coupled plasma 7 is instantaneously generated by the action of the high frequency magnetic field.

The ions in the glazma 7 red and white the nozzle 8 and the skimmer 9, and then pass through the ion lens system 14 and are focused. Here, the ion lens system 14 uses, for example, a tuple quadrupole lens that blocks light from the high-frequency inductively coupled plasma and passes only ions, and the ions that have passed through the ion lens system pass through the mass filter 16. The secondary electrons are guided to the secondary electron multiplier tube 19 and detected, and the detection signal is sent to the signal processing section 2.
The analyzed value of the element to be measured in the sample is obtained by sending the data to 0 and calculating and processing it.

Further, FIG. 4 is an explanatory diagram of the main part configuration of a conventional example showing the main parts of a conventional high frequency inductively coupled plasma mass spectrometer, and in the figure,
21 is an inlet side aperture plate having an opening 21' with an inner diameter of about 5 mm, and 22 is an opening 2 with an inner diameter of about 5 mm.
an outlet side aperture plate having 2-, 23a-2;
3h is the electrode (electrode [23d) of the 4[7-element lens] provided in two stages.

23h are not shown because they appear to overlap with electric terminals I#123b and 23f, respectively). In the main part of the conventional high-frequency inductively coupled plasma mass spectrometer having such a main part configuration, the light from the high-frequency induced plasma (i.e., the high-frequency inductively coupled plasma 8 in FIG. 3) is shown by the broken line arrow in FIG. 4. The light enters from the opening 21- of the inlet aperture plate 21 and hits the inner wall surface of the outlet aperture plate 22. Further, ions guided from the high-frequency inductively coupled plasma 7 in FIG. 3 through the nozzle 8, skimmer 9, etc. enter from the opening 21 of the inlet side aperture plate 21 as shown by the solid arrow in FIG. The ion beam is bent by the electric field of the camellia lenses 23a to 23h, and the center of the ion beam is shifted from the central axis from the high frequency inductively coupled plasma (which also coincides with the center of the high frequency inductively coupled plasma). The straight beam of light is blocked, and only ions from the high-frequency induced plasma exit through the opening of the exit-side aperture plate 22 and are detected by the secondary electron multiplier 19 shown in FIG.

<Problems to be solved by the invention> However, in the above conventional example, 41! Child lens 2
3a to 23d and quadrupole lenses 23e to 23h are
In the paper of Figure 4, if the vertical direction is the X axis, the vertical direction is the y axis, and the optical axis direction is the two axes, then the doublets are rotated 90 degrees around the Z axis, and two doublets are overlapped in the two axes. It is designed to function as a polar lens. That is, 1
The ions are diverged on the y-z plane of the second-stage quadrupole lenses 23a to 23d and converged on the y-z plane of the second-stage quadrupole lenses 23e to 23h, and the first-stage quadrupole lens 23
The ions are converged on the x-z plane of a to 23d and diverged on the x-z plane of the second-stage quadrupole lenses 23e to 23h. This slant allows ions to be focused on the average in both the yz plane and the xz plane, which has the following drawbacks.

■4 The number of elements in the 4-camellia lenses 23a to 23h is 8, and each electrode voltage has a complicated relationship with each other.
Voltage adjustment work (tuning) becomes a difficult work.

■Ion convergence is incomplete and the ion beam intensity reaching the mass filter tends to decrease, ultimately resulting in a decrease in sensitivity.

The present invention has been made in view of the drawbacks of the conventional examples, and its purpose is to provide a high-frequency inductively coupled plasma mass spectrometer equipped with an ion lens system that allows easy tuning of the ion lens and has high ion beam transmittance. Our goal is to provide the following.

Means for Solving the Problems> A feature of the present invention that solves the problems described above is that the ions generated by exciting a sample using high-frequency inductively coupled plasma are passed through an interface consisting of a nozzle and a skimmer. Quality 1 Analyzer In an analyzer that analyzes the element to be measured in the sample by guiding it to a detector, a pair of aperture plates having openings whose centers are mutually spaced are used to detect the element.
A set of parallel concave lenses is sandwiched between the two sets, and the optical axis of the first set of parallel concave lenses is aligned with the optical axis of the second set of parallel concave lenses. The reason is that an ion optical system is provided in which a voltage is applied to the concave lens symmetrically with respect to the average potential.

Function> The present invention functions as follows. That is, when a certain voltage is applied to the entrance aperture plate, the exit aperture plate, and the double parallel concave lens, the horizontal ion beam is bent downward by the action of the pair of parallel concave lenses on the entrance side. , this downward ion beam is bent horizontally by the action of a pair of parallel concave lenses on the J side. Therefore, the ion beam guided from the high frequency inductively coupled plasma through the opening of the entrance side aperture plate through a nozzle, skimmer, etc. becomes deviated from the central axis of the high frequency inductively coupled plasma. On the other hand, when the light from the high-frequency inductively coupled plasma enters through the openings of the entrance-side aperture plate 1, it travels straight and hits the inner wall surface of the exit-side aperture plate. Therefore, the light introduced from the high-frequency inductively coupled plasma and incident through the opening of the entrance aperture plate is blocked, and only the ion beam exits from the opening of the exit aperture plate. In addition, by placing the entire deflection lens system at a negative potential, divergence loss due to the ion beam can be reduced.
Ion transmission efficiency can be increased, resulting in improved detection sensitivity of the mass spectrometer.

<Example> Hereinafter, the present invention will be described in detail using the drawings. 1st
The figure is an explanatory view showing the main parts of the embodiment of the present invention. In the drawing, the same symbols as in FIG. 4 are used with the same meanings, and repeated explanation will be omitted here. Further, 24a and 24b are first and second parallel-concave lenses arranged to face each other to form a first set of parallel-concave lenses; 24c;
Reference numeral 24d indicates third and fourth parallel concave lenses that are arranged to face each other to form a second set of parallel concave lenses, and reference numerals 25a to 25c indicate variable voltage power supplies. Further, FIG. 2 is a diagram for explaining the positional relationship between the aperture plate 21° 22 and the parallel concave lenses 24a to 24d. Diagram looking in the direction of filter 17, (b)
(c) shows a view seen in the direction of the exit aperture plate 22 from a longitudinal cross section of the first parallel concave lenses 24a, 24b, and (c) shows a view seen in the direction of the exit aperture plate 22 from a cross section 1d of the entrance aperture plate 21. Furthermore, the second
In the figure, 26 is the first parallel concave lens 24a, 24b.
This is the space formed between them. Further, the same symbols as in FIG. 1 are used with the same meaning, and repeated explanations here will be omitted.

In the embodiment of the present invention having such a configuration, the first
As shown in the figure, voltages such that the following equations (1) to (3) are satisfied are applied from variable voltage power supplies 24a to 24d to the electrodes of the aperture plates 1 and 21.22 and the double parallel concave lenses 24a to 24d.

VaPI””VaP2・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・■vEI=vE
a・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・■VE2 ”VE3
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・■vEI>VE2...
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・■aV (VE + +VE 2 +VE 3 +VE a)
/4-...(5) Here, VaPI is a negative voltage of, for example, -40V applied to the inlet side aperture plate 21, and Vap2 is the negative voltage applied to the outlet flF1 aperture plate 2.
2, VE+ is a voltage of -30V, for example, applied to the electrode of the concave lens 24a, VE2 is a voltage of -50V, for example, applied to the electrode of the concave lens 24b, and VE3 is a voltage of -50V, for example, applied to the electrode of the concave lens 24b. For example, the voltage of -50V applied to t% of 24c, VEa is the concave lens 2
For example, the voltage of -30V applied to the @ pole of 4d, VaV
is the average voltage of the double parallel concave lenses 24a to 24d. However, the above equation 0 may deviate from this relationship to some extent depending on the energy of the incident ions.

In this way, the inlet side aperture plate 21° and the outlet side aperture plate 22. and parallel concave lens 24a~
When the above voltage is applied to the parallel concave lenses 24d, the horizontal ion beam is bent downward by the action of the parallel concave lenses 24a and 24b, and the parallel concave lenses 24c and 2
The downward ion beam is bent horizontally by the action of 4d. Therefore, the ion beam introduced from the high-frequency inductively coupled plasma 7 in FIG. 3 through the nozzle 8, skimmer 9, etc. and then guided from the opening 21 of the entrance side aperture plate 21 is explained in detail using FIG. As in the case of the conventional example described above, the beam is deflected from the axis of the high-frequency inductively coupled plasma 7 (hereinafter referred to as "first optical axis") midway. These deflected ions are deflected again by the parallel concave-convex lenses 24c and 24d, and connect an optical axis on an optical axis that is slightly shifted from the first optical axis. , “
The ion image is connected to the central axis of the mass filter 16 in FIG. 3 via the parallel concave lenses 24a to 24d so that the second optical axis (referred to as "second optical axis") coincides with the second optical axis.

On the other hand, the light from the high-frequency inductively coupled plasma 7 shown in FIG. 3 enters from the opening 21- of the entrance side aperture plate 21 shown in FIG. The optical path is blocked. Therefore, the light introduced from the high-frequency inductively coupled plasma and incident through the opening 21° of the entrance aperture plate 21 is blocked, and only the ion beam exits through the opening 22° of the exit aperture plate 22. Therefore, the background signal due to light is reduced, and the detection limit as a high frequency inductively coupled plasma mass spectrometer is ultimately improved.

Further, by setting the average potential VaV' of the entire ion lens system to a negative potential, divergence loss due to the ion beam can be reduced, ion transmission efficiency can be increased, and as a result, the detection sensitivity of the mass spectrometer is increased.

The above example is for the measurement of positively charged ions, but as a special measurement method, negative ions may be measured, and in this case, the lens configuration is the same as in this example, and the applied voltage is All you have to do is change the polarity from negative to positive, in this case,
The above equation 0 becomes the following equation (2), and the average potential (2)av of the entire ion lens system is assumed to be a positive potential.

VE H＜VE 2・・・・・・・・・・・・・・・・
・・・・・・・・・・・・■Furthermore, the present invention is not limited to the above-described embodiments, and can be modified in various ways. For example, the following (a) to (e) may be used. Make it good. (
b) Lenses for converging ions are arranged before and after the double parallel concave lenses 24a to 24d, and before and after the aperture lenses 21.22, and slits are arranged for blocking the entry of diverging and incident light. (b) Aperture lens 22
It also serves as a slit placed in front of the mass filter.

(c) The above formula 0 is converted into Vav-(VE + 10VE 2
+VE 3 +VE a +Vap, )15, or Va v = <VE I +VE2 +VE 3 +
VE 4 +Vap 2 )/5 is the average potential of five lenses including the aperture lens before or after the double parallel concave lens.

(d) Expression 0 above as Va v = (VE I +VE
2 +VE:I +VEa +Vap+ +Vap2
)/6 is the average potential of six lenses including the aperture lenses before and after the double parallel concave lens.

(e) The voltage value of each lens is independently adjusted slightly plus or minus without satisfying the relationship of the above formula 0 to 0.

<Effects of the Invention> The present invention as described in detail above involves exciting a sample using high-frequency inductively coupled plasma, guiding the generated ions to a mass spectrometer detector through an interface consisting of a nozzle and a skimmer, and detecting them. In the analyzer that analyzes the element to be measured in the sample, two sets of parallel concave lenses are sandwiched between a pair of aperture plates having apertures whose centers are shifted from each other, and the optical axis on the side of the first parallel concave lens is An ion optical system is provided in which the optical axis of the parallel concave lens of the second layer is shifted, and a voltage is applied symmetrically to the grain parallel concave lens and the parallel concave lens of the second layer with respect to the average potential. It was configured to provide.

Therefore, there is no ion divergence effect as in the conventional doublet quadrupole lens, and the ion lens system has a strong ion convergence effect, which has the advantage of ultimately improving detection sensitivity. Furthermore, since the method of applying voltage to the ion lens (double parallel concave lens) is simplified, ion tuning becomes easier and operability is improved.

Therefore, according to the present invention, a high-frequency inductively coupled plasma mass spectrometer is realized in which the ion lens is easy to tune, the ion beam transmittance is large, and the detection sensitivity is high.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the main part of the embodiment of the present invention, Fig. 2 is a diagram for explaining the positional relationship between the aperture plate and the parallel concave lens, and Fig. 3 is an overall view of the high frequency inductively coupled plasma mass spectrometer. FIG. 4 is an explanatory diagram of the main part of a conventional example. 1... Plasma torch, 3... Argon gas supply source, 7... High frequency inductively coupled plasma, 8...
・Nozzle, 9... Gap 16... Mass filter, 1... Secondary electron multiplier, 20...
...Signal processing unit 21.22...Aperture plate, 23a
~23h...Quadrupole lens electrodes 24a to 24d
・・・・・・Double parallel concave lens, 25a~25c・
...Variable voltage power supply Figure 1 Figure 3 Figure 2 (A) 1 port) (C) Figure 4

Claims (1)

[Claims] In an analyzer that analyzes the element to be measured in the sample by exciting the sample using high-frequency inductively coupled plasma and guiding the generated ions to a mass spectrometer detector through an interface consisting of a nozzle and a skimmer for detection, Two sets of parallel concave lenses are sandwiched between a pair of aperture plates having apertures whose centers are shifted from each other, and the optical axis of the first set of parallel concave lenses is shifted from the optical axis of the second set of parallel concave lenses, and A high-frequency inductively coupled plasma mass comprising an ion optical system in which a voltage is applied symmetrically to the first set of parallel-concave lenses and the second set of parallel-concave lenses with respect to an average potential. Analyzer.