JPS6411135B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical emission spectrometer, and particularly to an optical emission spectrometer using high frequency inductively coupled plasma.

Emission spectroscopy using high-frequency inductively coupled plasma (hereinafter referred to as ICP) as a light source has come to be used for the analysis of various trace metals, but ICP passes high-frequency power through a coil and generates a high-temperature plasma flame near it. It's something you make. To analyze metal elements using this ICP, a sample liquid containing the metal elements is made into a mist and introduced into a plasma flame to emit light, which is then introduced into an emission spectrometer for analysis.

Figure 1 is a cross-sectional view of an ICP plasma flame. A plasma flame 1 is generated by introducing a mist sample 4 into a quartz pipe 3 around which a coil 2 is wound and burning it together with fuel gas. Varies depending on type. This is because the difficulty of dissociation varies depending on the metal, and the degree of ionization differs.

Conventionally, such an ICP device was installed on a movable table, and the ICP device was adjusted by moving it up and down so that the optimal location of the plasma flame coincided with the optical axis on the input side of the spectrometer. However, recently there has been a demand for rapid analysis of 30 to 40 elements, and it has become necessary to select each element in synchronization with wavelength scanning. Rapidly moving the movable platform up and down to do this not only makes the plasma flame unstable, but also makes the ICP with a thick 2.5kW power cable attached.
It is an extremely difficult task to repeatedly move a device a predetermined distance vertically.
This is practically impossible.

An object of the present invention is to provide an optical emission spectrometer that eliminates the drawbacks of the prior art and enables highly accurate analysis by quickly and accurately selecting any bright spot of a plasma flame with a relatively simple configuration. a flame light source, a condenser lens positioned with its optical axis aligned with a horizontal plane containing the flame light source, a mirror that bends the light beam focused by the condenser lens downward, and the condenser lens. An entrance slit for forming a real image of the flame light source is formed in a direction parallel to the optical axis, and when the spectrometer installed in the vertical direction and the light emitting position of the flame light source are moved up and down, The apparatus is characterized by comprising means for moving the mirror in parallel on the optical axis in order to produce a real image of the light emitting position at the center of the incidence slit.

That is, in the case of the present invention, the light source remains fixed,
By changing the installation position of the entrance mirror of a vertical incidence spectrometer, an operation equivalent to the vertical movement of a conventional light source can be performed.

FIG. 2 is a perspective view of an optical emission spectrometer that is an embodiment of the present invention. The light of the plasma flame 1 of the ICP device is focused by a condenser lens 5 and bent downward by a plane mirror 6 to produce a real image of the plasma flame 1 on an entrance slit 7. The light beam that enters the spectrometer through the entrance slit 7 is reflected by the collimating mirror 8 and becomes a parallel light beam, which is then sent to the grating 9.
incident on . The parallel light beam diffracted by the grating 9 is reflected and focused by the camera mirror 10 to generate a spectrum on the surface of the exit slit 11. The monochromatic light beam selected by the output slit 11 is detected by a photomultiplier 12.

The above optical components are attached to the spectrometer base 13, and by rotating the feed screw 15 attached to the side surface of the spectrometer base 13 with a pulse motor 14, the sine bar 16 is rotated. The grating 9 attached to the shaft is rotated to scan the wavelength extracted from the output slit 11.

FIG. 3 is a right side view of the optical system of the spectrometer shown in FIG. and is detected by the photomultiplier 12. Although this spectrometer has a Zzerny-Turner arrangement, it is of course possible to use other types of spectrometers.

FIG. 4 is an explanatory diagram of the optical system from the light source to the entrance slit in FIG. It is reflected and enters the entrance slit 7.
That is, an image of the center of the plasma flame 1 with the highest brightness is formed on the entrance slit 7. However, depending on the type of sample 4, the location with the highest brightness may move to a relatively lower part of the plasma flame 1. At this time, the plane mirror 6 is moved back to the position shown by the broken line. That is, the image 18 of the plasma flame 1 after movement moves to the left as far as the broken line indicates, and the light below the center of the plasma flame 1 is taken in through the entrance slit 7.

This can be accomplished extremely easily and quickly since the objective can be achieved by simply moving the plane mirror 6 rather than by moving the conventional plasma flame 1 up and down. In addition, when the brightest point of the plasma flame 1 moves to the top of the flame, contrary to the above, the plane mirror 6 is advanced in the direction of the condensing lens 5 to bring the maximum amount of light into the spectroscope. It can be incorporated into the system to improve analysis accuracy.

Strictly speaking, by moving the plane mirror 6, the imaging position of the bright spot no longer coincides with the entrance slit 7, but in actual equipment, the length on the optical axis from the plasma flame 1 to the entrance slit 7 The height is about 70 cm, and even if the plane mirror 6 is moved back or forth by 1 cm, the image of the plasma flame 1 will hardly be blurred. This is because the thickness of the plasma flame 1 itself is about 2 cm, so it does not have any effect that reduces analysis accuracy. Further, chromatic aberration caused by a difference in the wavelength of the measurement light of the condenser lens 5 does not affect the analysis accuracy.

FIG. 5 is a side view of the plane mirror moving device of FIG. 4. A mounting base 20 on which the plane mirror 6 is fixed at an angle of 45 degrees is attached to a horizontal fine movement table 21, and this horizontal fine movement table 21 is moved in the direction of the arrow, that is, in the direction of the optical axis, by driving a pulse motor 19. Moving. Such an operation can be obtained, for example, by screwing the horizontal fine movement table 21 onto a screw formed on the rotating shaft of the pulse motor 19 and sliding a guide groove that is movable only in the optical axis direction. Note that 22 is a mounting plate to which these parts are mounted.

Figure 6 is a diagram showing the luminescence intensity distribution in the plasma flame. When a sample mist containing Ca is introduced into the plasma flame 1 and emitted, the luminescence intensity distribution of Ca with a dominant wavelength of 422.7 nm changes from the upper end of the coil 2. The emission intensity distribution of Ca with a dominant wavelength of 393.4 nm reaches its maximum at 18 mm from the top of the coil 2.
The position of maximum brightness of Ca moves by about 1 cm.
The position of the plane mirror 6 must therefore also be moved accordingly.

In this way, the observation position that gives the maximum intensity for the emission line of each element is measured in advance and stored in the storage device, so that the observation position can be automatically selected when measuring the element to be analyzed. In this device, a maximum of 70 elements can be stored in the computer. That is, the rotation speed of the pulse motor 1 is controlled by a command from a computer, and the plane mirror 6 is positioned at the optimum observation position simultaneously with wavelength scanning.

The above method mainly determines the position of the plane mirror 6 so that the point of maximum brightness of the plasma flame 1 coincides with the entrance slit 7, but in some cases, the observation position where the interference phenomenon is minimized may be determined. It may also be stored in memory.

By forming the spectrometer vertically as shown in FIG. 2, this emission spectrometer can be functionally combined with an ICP device that must be installed vertically. In other words, the installation space of the entire device can be reduced to make it compact, and
An advantage is obtained that the moving mechanism for the plane mirror 6 as described above can be installed in the horizontal direction and formed rationally.

The optical emission spectrometer of this example has a vertical spectrometer, by moving a plane mirror that bends and introduces the light from the light source into the entrance slit of the vertical spectrometer in the optical axis direction.
This provides the advantage that fluctuations in brightness distribution due to time differences in dissociation phenomena in flame can be automatically corrected and highly accurate measurements can be performed quickly.

Although the above embodiment uses a plane mirror 6, a real image of the plasma flame 1 can be formed using not only a plane mirror but also a curved surface mirror, such as a toroid concave mirror. Also,
Similar results can be obtained by displacing the condensing lens 5 in the vertical direction with respect to the optical axis, but the mechanism is complicated and there is a risk that the selection accuracy will be reduced.

Although the above embodiment has been described using an example of emission spectrometry using ICP as a light source, it can also be applied to other types of emission spectrometry in which the light emission position changes as the wavelength changes.

The emission spectrometer of the present invention has the effect of enabling highly accurate analysis with a relatively simple configuration.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the ICP plasma flame, Fig. 2 is a perspective view of an optical emission spectrometer that is an embodiment of the present invention, and Fig. 3 is a right side view of the optical system of the spectrometer shown in Fig. 2. Figure 4 is an explanatory diagram of the optical system from the light source to the entrance slit in Figure 2, Figure 5 is a side view of the plane mirror moving device in Figure 4, and Figure 6 shows the emission intensity distribution in the plasma flame. It is a line diagram. 1... Plasma flame, 2... Coil, 3... Quartz pipe, 4... Sample, 5... Condensing lens, 6...
Plane mirror, 7... Input slit, 11... Output slit, 12... Photomultiplier, 13...
...Spectrometer base, 14,19...Pulse motor,
15...Feed screw, 16...Sine bar, 20...
...Mounting base, 21...Horizontal fine movement table, 22...
mounting plate.

Claims (1)

[Claims] 1. A flame light source, a condenser lens positioned with its optical axis aligned with a horizontal plane containing the flame light source, and a mirror that bends the light beam focused by the condenser lens downward. , an entrance slit for forming a real image of the flame light source by the condenser lens is formed in a direction parallel to the optical axis, and a spectroscope installed in the vertical direction and a light emitting position of the flame light source are vertically aligned. and means for moving the mirror in parallel on the optical axis in order to produce a real image of the light emission position at the center position of the incidence slit when the mirror is moved to the center of the entrance slit. . 2. Memorize the optimal position of the mirror on the optical axis for observing each bright line generated by the flame light source, and change the position of the mirror on the optical axis in synchronization with the wavelength scanning of each bright line. An emission spectroscopic analyzer according to claim 1, which is configured as set.