JP4116214B2 - High frequency inductively coupled plasma optical emission spectrometer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-frequency inductively coupled plasma optical emission spectrometer, and more particularly to an apparatus using a two-dimensional surface detector.
[0002]
[Prior art]
Conventionally, an apparatus using a photomultiplier tube instead of a two-dimensional surface detector has been used. In an apparatus using a photomultiplier tube, only the light intensity of a specific wavelength can be measured. Therefore, when measuring the light intensity of a nearby wavelength, it is necessary to move the wavelength of the spectrometer minutely.
[0003]
[Problems to be solved by the invention]
When a photomultiplier tube is used, the spectroscope is configured so that only the light to be analyzed enters the detector. Therefore, in order to acquire data in the vicinity of the target wavelength, it is necessary to slightly drive the wavelength of the spectrometer. If the photomultiplier tube is simply replaced with a two-dimensional surface detector, all the light in the vicinity of the light to be analyzed can enter, but it can be measured in a short time with a photomultiplier tube. In the surface detector, since it takes time to transfer the charge after exposure, it takes time to acquire data. If there is a weak light peak in the vicinity of the strong light peak, it is necessary to divide the exposure time into a strong light and a weak light and perform exposure twice.
[0004]
[Means for Solving the Problems]
In order to divide the dispersed light before imaging into different directions, a light splitting device is arranged on the optical axis, and a plurality of light blocking devices and two-dimensional surface detectors are provided on the split optical path. .
[0005]
[Action]
By using a plurality of light blocking devices and a two-dimensional surface detector and measuring each with an exposure time for strong light and weak light, measurement near the target wavelength can be performed at a time. In addition, while one of the two-dimensional surface detectors is transferring charges, the other exposure can be performed, so that the measurement time can be shortened.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, it will be described in detail based on examples.
FIG. 1 shows an embodiment of the present invention. Plasma 1 is generated by a plasma generator (not shown), a sample is introduced into plasma 1 by a sample introduction device (not shown), and light used for analysis is emitted from plasma 1. The light emitted from the plasma 1 is condensed on the entrance slit 3 by the lens 2, becomes parallel light by the collimating mirror 4, the parallel light is split by the grating 5, and the split light is imaged by the camera mirror 6. The A light splitting device 7 is disposed on the optical path immediately before the image is formed, and the transmitted light passes through the light blocking device A8 and forms an image on the two-dimensional surface detector A9. The image is formed on the surface detector B11.
[0007]
A half mirror in which aluminum was vapor-deposited on a quartz plate was used as the light splitter 7. By changing the thickness of the deposited aluminum film, the ratio of transmission to reflection can be changed. As another method, a part of a disk having a mirror surface was cut into a plurality of strips, and a motor was attached to the center for rotation. The ratio of transmission and reflection can be changed by increasing the number of parts to be cut.
[0008]
The light blocking devices 8 and 10 used mechanical shutters, and the two-dimensional surface detectors 9 and 11 used CCDs (charge coupled devices). The detector may be a CID or a diode array, and is not limited to a CCD.
First, a case where the ratio of transmitted light to reflected light is 1 (transmitted light: reflected light = 1: 1) will be described.
[0009]
When measuring a plurality of analysis lines, if a two-dimensional detector is used, it takes time to transfer charges, and therefore, it takes more measurement time. Therefore, as shown in FIG. 3, while the light blocking device A8 is opened and closed and the charge is read after the exposure of the two-dimensional surface detector A9, the grating 5 is driven to move the wavelength, and then the light blocking device B10 is moved. It can be opened and closed and exposed by the two-dimensional surface detector B11. While reading the electric charge after the exposure is finished by the two-dimensional surface detector B11, after the grating 5 is driven again and the wavelength is moved, the light blocking device A8 can be opened and closed and the two-dimensional surface detector A9 can perform the exposure. In this way, the measurement time can be shortened by alternately exposing a plurality of light blocking devices and two-dimensional detectors and reading out the charges.
[0010]
When strong light and weak light are mixed in the measurement range of the two-dimensional surface detector, when the exposure is based on the strong light, the weak light cannot be detected with sufficient intensity, and conversely, the exposure is based on the weak light. In this case, strong light is saturated and cannot be measured. For this reason, it is necessary to expose and read twice, which takes time. At this time, as shown in FIG. 4, the opening time of the light blocking device A8 is lengthened, the exposure time of the two-dimensional surface detector A9 is set longer for weak light, and the opening time of the light blocking device B10 is shortened. By setting the exposure time of the two-dimensional surface detector B11 to be short for strong light, data of strong light and weak light can be obtained with one exposure, and the measurement time can be shortened.
[0011]
The actual measurement data is shown in FIG. This is the result when A is exposed for 2 seconds and B is exposed for 1 second. In the case of exposure (A) for 2 seconds, the rightmost peak is saturated, but the second peak shows almost the maximum intensity. Moreover, the peak of 2 second exposure (A) was twice the peak of 1 second exposure (B), and it was confirmed that the measurement was performed properly.
[0012]
Next, a case where the ratio of transmitted light to reflected light is 4 (transmitted light: reflected light = 4: 1) will be described. The ratio of transmitted light to reflected light is not limited as long as it is 1 or more.
As described above, when strong light and weak light are mixed in the measurement range of the two-dimensional surface detector, weak light cannot be detected with sufficient intensity when exposed to strong light, but weak light is conversely When the exposure is performed based on, strong light is saturated and cannot be measured. Although good results can be obtained by measuring at different exposure times, time fluctuations may occur while one is still exposed after the other. Therefore, measurement is performed at the same time with the same exposure time as shown in FIG. The light transmitted through the light splitting device 7 passes through the light blocking device A8 and forms an image on the two-dimensional surface detector A9. The reflected light passes through the light blocking device B10 and forms an image on the two-dimensional surface detector B11. The light intensity at this time is the same as the transmission / reflection ratio, and A: B = 4: 1. That is, the light intensity ratio between the two-dimensional surface detector A9 and the two-dimensional surface detector B11 having the same exposure time is 4: 1. Even in this case, data of strong light and weak light can be obtained by one exposure, and data that is not affected by temporal fluctuation can be obtained.
[0013]
【The invention's effect】
By using a plurality of two-dimensional surface detectors, the intensity of many wavelengths can be measured in a short time. Also, a strong light intensity peak and a weak light intensity peak can be measured simultaneously.
[Brief description of the drawings]
FIG. 1 is an embodiment of the present invention.
FIG. 2 is a conventional example.
FIG. 3 is a timing chart during sequential measurement.
FIG. 4 is a timing chart for different exposure times.
FIG. 5 is a timing chart when the division ratio of the light dividing device 7 is different;
FIG. 6 shows actual spectrum data.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Plasma 2 Lens 3 Entrance slit 4 Collimating mirror 5 Grating 6 Camera mirror 7 Light splitting device 8 Light blocking device A
9 Two-dimensional surface detector A
10 Light blocking device B
11 Two-dimensional surface detector B
12 Exit slit 13 Photomultiplier tube

Claims (4)

A high-frequency inductively coupled plasma generator, a sample introduction device that introduces a sample into the plasma, an incident optical system that guides light emitted from the plasma to an entrance slit, a collimating mirror that converts light from the entrance slit into parallel rays, A grating that divides parallel rays, a camera mirror that forms an image of the dispersed light, a two-dimensional surface detector that detects the dispersed light that is placed on the imaging surface, and is placed immediately before the two-dimensional surface detector. In a high-frequency inductively coupled plasma optical emission spectrometer comprising a light blocking device that controls the incidence of light on a two-dimensional surface detector, on the optical axis that divides the dispersed light before imaging into another direction A high frequency inductively coupled plasma emission spectroscopic analysis apparatus comprising: a light splitting device disposed; and a plurality of light blocking devices and two-dimensional surface detectors on the split light path. 2. The high frequency inductively coupled plasma emission spectrometer according to claim 1, wherein the light splitting device is a mirror disposed at an angle of 45 degrees on the optical axis, and is a half mirror capable of splitting into transmitted light and reflected light. . The light splitting device is an optical chopper that can be split into transmitted light and reflected light by rotating a disk that is arranged at an angle of 45 degrees on the optical axis and in which reflecting surfaces and openings are alternately arranged. The high frequency inductively coupled plasma optical emission spectrometer according to claim 1. 4. The high frequency inductively coupled plasma emission spectrometer according to claim 2, wherein the ratio of transmitted light / reflected light of the light splitting device is 1 or more.

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