JP2895816B2 - ICP emission spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for the analysis of trace elements such as lead contained in tap water and various elements contained in wastewater, and is used for ICP (Inductively Coupled Plasm).
a: Inductively coupled plasma) as an emission source for elemental analysis.

[0002]

2. Description of the Related Art A conventional ICP emission spectrometer is shown in FIG.
As shown in (1), it is composed of a plasma torch 1 provided with a high-frequency induction coil 11, a condenser lens 2, one spectroscope 3, and one detector 4. Further, the spectroscope 3 is provided therein with an entrance slit 31, a collimator mirror 32, a diffraction grating (dispersor) 33, a camera mirror 34, and an exit slit 35.

[0003] When analyzing the element to be measured, a solution sample Q containing the element to be measured in the high-temperature gas is supplied to the plasma torch 1 together with a plasma generating gas such as an argon gas. At the same time, the high-frequency induction coil 11 is energized to generate a strong magnetic field and heat it to produce an inductively coupled plasma P in which the element to be measured is contained in argon gas. Light emitted by the plasma P is condensed by the condenser lens 2, enters the inside of the spectroscope 3 from the entrance slit 31, is reflected by the collimator mirror 32, and enters the diffraction grating 33. The diffraction grating 33 selects the wavelength of the light from the collimator mirror 32 by selecting the rotation angle, and diffracts the light. The diffracted light is emitted from the camera mirror 34 to the outside of the spectroscope 3 through the emission slit 35, The emitted light is detected by the detector 4.

[0004]

The above-mentioned ICP emission spectrometer has the features that it has high sensitivity (detection limit), can perform elemental analysis in ppb units, and can perform stable measurement. It is desired that this feature be further enhanced. However, as described above, when the light beam from the plasma P is incident on one spectroscope 3 and the outgoing light beam is detected by only one detector 4, local fluctuation of the plasma P (flicker noise source) occurs. There is a limit to improving stability because it is more susceptible.

In order to improve the sensitivity, the amount of light rays taken from the plasma P into the spectroscope 3 may be increased. However, for the following reasons, it is difficult to increase the amount of light rays taken in, and the light emission utilization rate of the plasma P becomes small, so that the sensitivity cannot be further improved.

That is, in the above-mentioned spectroscope 3, the grating interval of the diffraction grating 33 is d (mm), the focal length of the collimator mirror 32 is f (mm), and the wavelength of the m-th order diffracted light is λ (mm).
Assuming that the diffraction angle of the diffraction grating 33 at the time is β, the linear dispersion (dispersion distance on the exit slit surface / wavelength) D is as follows. D = (f · m) / (d · cos β) Here, in the general spectroscope 3, f = 500 m
Since m, m = 1, d = 1/4000, and β = 60 °, D = 4,000,000 (= t).

At the time of analysis, the proximity line (noise component)
In order to increase the resolution by eliminating the influence of the wavelength, it is desirable to minimize the wavelength resolution (corresponding to the reciprocal of the resolution) in the spectroscope 3 as much as possible. At present, the ultraviolet region (200
(near nm), a wavelength resolution of 0.01 nm (= u) is achieved.

The size of the opening of each of the slits 31 and 35 for obtaining the above-mentioned resolution of 0.01 nm is obtained by t × u and is 0.04 mm.

On the other hand, the plasma P generated by the plasma torch 1 is condensed by the condenser lens 2 and is incident on the entrance slit 31.
A plasma image is formed at a time, but the magnification of this image is only about 1. Normally, the effective diameter of plasma P (the diameter of a portion usable for emission spectroscopy) is about 15 mm, and the circumferential distance thereof is about 50 mm.
mm, the opening size of the entrance slit 31 is very small, 0.04 mm.
The width of the plasma P taken into the spectroscope 3 from 1 and used for analysis is very small, about 0.2 mm, and the luminous utilization is less than 0.1%. Thus, the plasma P
Because of the low light emission utilization rate, there is a limit to improving the sensitivity.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above, and has been made in view of the above. An IC capable of improving the sensitivity by further increasing the efficiency of plasma emission and performing more stable analysis.
An object of the present invention is to provide a P emission spectrometer.

[0011]

In order to achieve the above object, an ICP emission spectrometer according to the present invention has a plasma torch for generating a plasma containing an element to be measured and a light beam from the plasma for spectroscopy. A plurality of spectroscopes that emit light beams of a wavelength from a single exit slit, driving means for driving the spectroscope to change the wavelength to be selected, and arranged corresponding to each of the spectroscopes and emitted from the exit slit A plurality of detectors for detecting light beams, and a control unit for controlling the driving unit so that the plurality of spectroscopes simultaneously select the same wavelength,
A calculating means for adding or subtracting the outputs of the plurality of detectors, wherein the plurality of spectroscopes are set to split light beams from different portions of the plasma.

In the above configuration, at the time of analysis, plasma containing the element to be measured is generated by the plasma torch, and light beams from different peripheral portions of the plasma enter the plurality of spectroscopes. At this time, each spectroscope is driven by the driving means so that an arbitrary wavelength can be selected. The driving means controls the control means so that each spectroscope simultaneously selects the same wavelength. Then, light beams having the same wavelength selected by each spectroscope are emitted to the outside from the emission slit, and are detected by detectors provided in each spectroscope. Output signals from these detectors are subjected to addition or subtraction processing by arithmetic means, and the results are output as external signals.

As described above, by measuring the light beams from a plurality of different portions around the plasma, even if the plasma has local fluctuations, the measured values of the light beams at each portion are averaged. Therefore, the stability at the time of analysis is improved. In addition, the amount of light taken in by the entire apparatus increases, and the light emission utilization rate of plasma is increased.
The (signal / noise) ratio is improved and the sensitivity is improved. In addition, when the output signal from each detector is calculated by the calculating means, when the addition processing is performed, the signal of the element to be measured is added, and the signal peak increases, whereas the noise has a phase difference, Even if these noise components are added, the signal peak does not become so high, so that the S / N ratio is improved,
The element to be measured is analyzed with high sensitivity. On the other hand, when the subtraction process is performed, the signal peak of the element to be measured becomes smaller, but the noise has a phase difference, and these noise components remain to some extent even after the subtraction, so that the noise level can be roughly estimated. Therefore, it is possible to evaluate the measured value, for example, by roughly evaluating the S / N ratio and determining that the measured value is valid only when the value is equal to or more than a certain value. In this case, the noise component can be easily analyzed.
It is also possible to check the background state at the time of analysis.

In a preferred embodiment of the present invention, different portions of the plasma, into which light beams enter each spectroscope, are set at the same height of the vertically extending plasma. According to this configuration, since light beams from the same height at which the plasma has a substantially uniform temperature are incident on each spectroscope, accurate analysis can be performed with uniform light emission intensity of the incident light beams on each spectrometer.

Further, in a preferred embodiment of the present invention, the same wavelength selected by a plurality of spectroscopes is set so that the wavelength error between them becomes 0.2 nm or less. If the wavelength error is within this range, it can be regarded as the same element, so that good analysis can be performed even if each spectrometer has a slight driving error.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, an ICP emission spectrometer includes a plurality of sets of a measurement system including a condenser lens 2, a spectroscope 3, and a detector 4 provided around an outer periphery of a plasma torch 1 at the same distance from the torch 1 in a radial direction. And, for example, as shown in FIG. 2, they are arranged 180 ° apart in the circumferential direction. At this time, the condenser lens 2 and the spectroscope 3 of each set in FIG. 1 are arranged such that their optical axes are located on the same circumferential line at the intermediate height position of the plasma P in the vertical direction. Since the devices provided around the plasma torch 1 are the same as the conventional devices, the same devices are denoted by the same reference numerals, and detailed description thereof will be omitted.

The diffraction grating 33 of each spectroscope 3 is provided with a driving means 5 such as a motor for rotating the diffraction grating 33 so as to select different wavelengths of the light beam reflected from the collimator mirror 32. Each driving means 5 is connected to a control means 6, and this control means 6 outputs an instruction signal to each driving means 5 so that each spectroscope 3 simultaneously selects the same wavelength.

Further, each detector 4 has an amplifier 7
The output of the arithmetic means 8 is input to an analyzer 9 to calculate the element concentration and the like.

Next, the operation of the ICP emission spectrometer configured as described above will be described. In plasma torch 1,
A liquid sample Q such as tap water or factory drain is supplied together with a plasma generation gas such as an argon gas, and a high-frequency induction coil is energized to generate a plasma P extending in a vertical direction. The light beam from the plasma P is condensed by each set of condensing lenses 2 arranged around the periphery thereof, and the spectroscope 3 separates the emission line corresponding to the element to be measured, and then splits the light into a detector 4
Incident on.

At this time, the diffraction grating 33 in each spectroscope 3
Are rotated by the respective driving means 5 to select and diffract the wavelength of light reflected from the collimator mirror 32. Also,
Each drive unit 5 is controlled by the control unit 6 to cause each diffraction grating 33 to simultaneously select the same wavelength. Here, those having an error of the wavelength selected by each diffraction grating 33 of 0.2 nm or less are regarded as the same wavelength. This allows a slight drive error when controlling the drive of each diffraction grating 33. Light beams of the same wavelength selected by each diffraction grating 33 are emitted to the outside through the emission slits 31 of each spectroscope 3, and each detector 4 detects this.

The signals from the detectors 4 are respectively amplified by an amplifier 7 and input to an arithmetic means 8. The arithmetic means 8 performs addition or subtraction processing, and the processed signal is processed by an analyzer 9. , The concentration of the element, the level of the noise component, etc., and output the calculation result. In the case of performing the addition processing in the arithmetic means 8, as described above, the element to be measured is analyzed with good sensitivity. On the other hand, when the subtraction process is performed, the validity of the measured value of the light emitting line can be determined by performing a rough evaluation of the noise level. Also, the background state at the time of analysis can be checked.

As described above, by taking light beams from a plurality of different portions around the periphery of the plasma P into the respective spectroscopes 3 and analyzing them, the amount of light beams taken in as a whole increases, and the light emission of the plasma P is utilized. Rate is increased, so S / N
The ratio is improved and the sensitivity is improved. In addition, it is hardly affected by flicker noise and the like, and the stability at the time of analysis is improved. In addition, since the optical axes of the plurality of spectroscopes 3 are arranged on the same circumferential line at an intermediate height position of the plasma P in the vertical direction, the light is incident on each spectrometer 3 from a portion of the plasma P having substantially the same temperature. In addition, accurate analysis can be performed by adjusting the emission intensity to each spectrometer 3.

It should be noted that three or more measurement systems including the condenser lens 2, the spectroscope, and the detector 4 may be provided. In that case, the outputs from all the detectors 4 are added, and if necessary, the outputs from the two detectors are subtracted.

[0024]

As described above, according to the ICP emission spectroscopy analyzer of the present invention, the sensitivity can be improved by increasing the efficiency of plasma light emission, and it is hardly affected by local fluctuations of the plasma. Thus, stable analysis can be performed.

[Brief description of the drawings]

FIG. 1 is a side view of an ICP emission spectrometer according to the present invention.

FIG. 2 is a plan view of the same device.

FIG. 3 is a side view showing a conventional ICP emission spectrometer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Plasma torch, 3 ... Spectroscope, 35 ... Emission slit, 4 ... Detector, 5 ... Drive means, 6 ... Control means, P ... Plasma.

Continuation of the front page (56) References JP-A-60-237346 (JP, A) JP-A-2-201141 (JP, A) JP-A-62-63841 (JP, A) JP-A-58-66839 (JP, A) , A) Actually open sho 57-66755 (JP, U) Really open sho 62-73250 (JP, U) Actually open sho 56-82544 (JP, U) Really open sho 62-140438 (JP, U) Real open 57-104344 (JP, U) Japanese Utility Model 62-134052 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 21/73

Claims (3)

(57) [Claims] A plasma torch for generating a plasma containing an element to be measured; a plurality of spectroscopes for dispersing light from the plasma to emit light of a selected wavelength from a single exit slit; A driving means for driving a device to change a wavelength to be selected; a plurality of detectors arranged corresponding to each spectrometer for detecting light beams emitted from the exit slit; and the plurality of spectrometers being simultaneously the same. Control means for controlling the driving means so as to select a wavelength, and arithmetic means for adding or subtracting the outputs of the plurality of detectors, wherein the plurality of spectroscopes are different from each other in the plasma. An ICP emission spectrometer set to split light. 2. The plasma processing apparatus according to claim 1, wherein the different portions of the plasma are located at the same height of a vertically extending plasma.
CP emission spectrometer. 3. The plurality of spectroscopes according to claim 1, wherein the same wavelength in the plurality of spectroscopes has a wavelength error of 0.2 n.
m or less.