JP2003014631A - Atomic absorption spectrophotometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the loss of light in the optical system of an atomic absorption spectrophotometer. SOLUTION: Luminous flux Ls on a sample side is condensed to an atomization part 8 by a toroidal mirror 4 and a plane mirror 5 and subsequently condensed to a chopper mirror 11 by a concave spherical mirror 9 and a plane mirror 10 while luminous flux Lr on a reference side is condensed to the chopper mirror 11 by a toroidal mirror 6 and a plane mirror 7. The convergent magnifications of both luminous fluxes are made equal by the chopper mirror 11. By this constitution, the loss of light in the chopper mirror 11 is reduced and the condensing efficiency to an inlet 14 is also enhanced. Since the changeover of both luminous fluxes accompanied by the rotation of the chopper mirror 11 is rapidly performed, a sampling time can be ensured long in a detection signal and an S/N ratio is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an atomic absorption spectrophotometer, and more particularly to an atomic absorption spectrophotometer using a double beam optical system.

[0002]

2. Description of the Related Art FIG. 3 is a schematic optical path configuration diagram of a double beam optical system in an atomic absorption spectrophotometer. Light source 21
The light emitted from is split by the half mirror 22 into two light fluxes, a sample-side light flux Ls and a reference-side light flux Lr. The sample-side light flux Ls that has traveled straight passes through the atomization section 23, and at that time, is absorbed by the wavelength corresponding to the sample and reaches the chopper mirror 26. On the other hand, the reference-side light flux Lr reflected by the half mirror 22 reaches the chopper mirror 26 via the reflecting mirrors 24 and 25. The chopper mirror 26 sequentially selects the sample-side light beam Ls and the reference-side light beam Lr in synchronization with the rotation of the motor 27, and the spectroscope 28
It sends it to one optical path toward. Generally, the sample side luminous flux L
s is condensed by an unillustrated condensing optical system at two points of the atomization part 23 and the entrance slit of the spectroscope 28, while the reference side light flux Lr is condensed only by the entrance slit of the spectroscope 28. Has been done.

In the spectroscope 28, only the wavelength component corresponding to the target element is selected and sent to the detector 29. The sample-side light beam Ls is absorbed by the atomization section 23, whereas the reference-side light beam Lr shows the brightness fluctuation of the light source 21 as it is, except for the negligible and negligible absorption by the reflecting mirrors 24 and 25. Therefore, at the same time (chopper mirror 26
By calculating the ratio of the light intensity with respect to the sample-side light beam Ls and the light intensity with respect to the reference-side light beam Lr (ignoring the time lag due to Eq. it can.

[0004]

To improve the performance of such an atomic absorption spectrophotometer, the main problems in the optical system are as follows. First, if the loss of light on the optical path is large, the amount of light that finally reaches the detector 29 will be small, and it will be difficult to improve the measurement sensitivity and accuracy.
In the optical path configuration of a conventional atomic absorption spectrophotometer, light is blocked in the atomization part (for example, in the case of the frameless system, light is blocked in a graphite tube) or when passing through the entrance slit of the spectrometer. Light loss is large, and it is necessary to reduce such light loss as much as possible.

Second, the sample side light flux Ls and the reference side light flux Lr
If the conditions are not satisfied, the influence of the fluctuation of the brightness of the light source 21 cannot be completely canceled out, which causes the deterioration of the measurement accuracy. The baseline drift at the time of measurement due to the brightness variation of the light source 21 is considerably reduced by sufficiently warming up the hollow cathode lamp, which is the light source 21, but is measured by increasing the scale expansion ratio of the absorbance. In many cases, the drift will also be enlarged and cannot be ignored.

The present invention has been made in view of the above points, and its main purpose is to reduce the light loss, and the conditions of the light flux on the sample side and the light flux on the reference side are uniform, so that the variation in the brightness of the light source can be suppressed. An object of the present invention is to provide an atomic absorption spectrophotometer equipped with an optical system capable of sufficiently canceling the influence.

[0007]

Means for Solving the Problems and Effects The present invention made to solve the above problems is to divide light emitted from a light source into a sample side light beam and a reference side light beam by a half mirror,
In the atomic absorption spectrophotometer, the sample-side light flux is passed through the atomization unit, and then both light fluxes are selected by a chopper mirror to irradiate the entrance slit of the spectroscope. And between the atomization part and the chopper mirror, a sample side front optical system and a sample side rear optical system through which the sample side light flux passes are respectively arranged, and between the light source and the chopper mirror. A reference side optical system through which the reference side light beam passes, and a common optical system is further arranged between the chopper mirror and the entrance slit, and the sample side light beam is condensed on the atomization part by the sample side front optical system. After that, the sample-side rear optical system refocuses the light on the chopper mirror, while the reference-side light beam is focused on the chopper-mirror by the reference-side optical system, and both light beams are on the entrance slit by the common optical system. Focused on It is characterized by comprising been.

That is, in this atomic absorption spectrophotometer,
Conventionally, by converging both light fluxes on the chopper mirror surface that has not been condensed, the efficiency of light convergence on the entrance slit surface is further enhanced, and the light loss at the entrance slit is reduced. . Further, when the spot diameter of the light on the chopper mirror surface becomes small, the light to be reflected does not run off the mirror surface and hits the mirror surface without fail, so that the loss of light also decreases. From this, according to the atomic absorption spectrophotometer of the present invention, it is possible to suppress the loss of light, increase the amount of light finally introduced into the detector, and improve the analysis sensitivity and accuracy. . Furthermore, if the spot diameter of the light on the surface of the chopper mirror is small, the passage / blocking of the light and the switching of the light flux are rapidly performed with the rotation of the chopper mirror, so that the detection is performed during the period of one rotation of the chopper mirror. It is possible to take a long time to sample the detection signal of the container. As a result, more detection signals can be accumulated correspondingly, which also improves the analysis sensitivity and accuracy.

Further, in the atomic absorption spectrophotometer according to the present invention, in the sample side front optical system, an F number directed to the atomization section side is set to be larger than an F number directed to the light source side. It is characterized by becoming.

According to this structure, a large amount of light can be taken in to the light source side, while the opening angle of the incident light with respect to the optical axis in the atomization part is small, so that the atomization part The light eclipse is reduced to that extent and the light loss is suppressed. However, the larger the difference between the F-numbers facing the light source side and the atomization portion side, the larger the aberration of the optical system and the larger the device itself. Therefore,
The ratio of the F number is larger than 1 and is about 2 times at maximum, preferably about 1.2 to 1.5 times.

Further, in the atomic absorption spectrophotometer according to the present invention, the sample side front optical system, the sample side rear optical system, and the reference side optical system converge both light beams focused on the chopper mirror. It is characterized in that the magnifications are configured to be substantially equal. According to this configuration, since the spot diameters of both light fluxes are almost the same on the chopper mirror surface, the conditions of both light fluxes are almost the same except that the sample-side light flux has passed through the atomization section, and the brightness variation of the light source is It is possible to accurately offset such fluctuation factors.

[0012]

DETAILED DESCRIPTION OF THE INVENTION An atomic absorption spectrophotometer according to an embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is an optical path configuration diagram excluding a photodetector of the atomic absorption spectrophotometer according to the present embodiment.

This optical system can be roughly divided into a measurement optical system A including an atomization section 8 and a spectroscopic optical system B. The spectroscopic optical system B is
It is a so-called Czerni-Turner type monochromator composed of an entrance slit 14, concave spherical mirrors 15 and 17, a plane diffraction grating 16 and an exit slit 18. On the other hand, the measurement optical system A is a first hollow cathode lamp (HCL).
Light source 1, second light source 2 which is a deuterium lamp (D2L), half mirror 3, first toroidal mirror 4, first plane mirror 5, second toroidal mirror 6, second plane mirror 7, atomization section 8, first concave Spherical mirror 9, third plane mirror 10, chopper mirror 11, fourth
The plane mirror 12 and the second concave spherical mirror 13 are included. Here, the first toroidal mirror 4 and the first plane mirror 5 are the sample side front optical system, the first concave spherical mirror 9 and the third plane mirror 10 are the sample side rear optical system, the second toroidal mirror 6 and the second plane mirror. Reference numeral 7 corresponds to the reference side optical system, and the fourth plane mirror 12 and the second concave spherical mirror 13 correspond to the common optical system.

The second light source 2 is provided for background absorption correction processing and is not essential in the atomic absorption spectrophotometer according to the present invention. Therefore, the second light source 2 will not be particularly referred to in the following description.

The above structure will be described in detail according to the path through which the light flux passes. The light beam emitted from the first light source 1 is split by the half mirror 3 into a sample-side light beam Ls and a reference-side light beam Lr. The sample-side light beam Ls reflected by the half mirror 3 is condensed by the sample-side front optical system including the first toroidal mirror 4 and the first plane mirror 5 at the atomization section 8 at a magnification of 1.33. When the sample side light flux Ls passes through the atomization part 8,
The amount of light decreases due to absorption at a wavelength according to the type of sample and according to its concentration. Then, the first concave spherical mirror 9, the third
The sample-side rear optical system including the plane mirror 10 focuses the light on the chopper mirror 11 at a magnification of 1. Therefore, an image of the first light source 1 magnified 1.33 times is formed on the chopper mirror 11.

On the other hand, the reference-side light flux Lr that has traveled straight through the half mirror 3 is condensed by the reference-side optical system including the second toroidal mirror 6 and the second plane mirror 7 on the chopper mirror 11 at a magnification of 1.33. That is, in the chopper mirror 11, the sample-side light flux Ls and the reference-side light flux Lr have the same magnification, and theoretically have the same spot diameter. The chopper mirror 11 is rotationally driven by a motor (not shown), and sends the sample-side light flux Ls and the reference-side light flux Lr alternately to the fourth plane mirror 12 in synchronization with the rotation cycle. The common optical system including the fourth plane mirror 12 and the second concave spherical mirror 13 focuses the above-mentioned alternating light flux on the entrance slit 14 at a magnification of 1 / 1.33. Therefore, the entrance slit 14 has a magnification of 1, that is, the first light source 1.
An image of the same size as is formed.

The light passing through the entrance slit 14 is condensed in one direction by the concave spherical mirror 15 and sent to the plane diffraction grating 16, where it is wavelength-dispersed in the orthogonal direction. Then, by the concave spherical mirror 17, the exit slit 1 is formed in the direction orthogonal to the wavelength dispersion.
Only light in a very narrow wavelength range is condensed at 8, and is extracted from the exit slit 18.

One of the features of the above optical system is that both light fluxes are once condensed on the chopper mirror 11.

In the configuration of the optical system shown in FIG. 1, the result of calculating the image formation (ray trace) on the chopper mirror 11 by computer simulation is shown in FIG. The image simulation result is shown in FIG. Since the optical system of the conventional device does not focus the light on the chopper mirror surface, both the sample-side light flux and the reference-side light flux are images that greatly extend in the longitudinal direction.
Even if this image was focused on the entrance slit, a large amount of light was lost at the entrance slit. On the other hand, in the device according to the present embodiment, the spot diameter is small on the surface of the chopper mirror 11 as shown in FIG. Light loss is extremely low.

Further, if the spot diameter of the light is small in the chopper mirror 11, there are the following advantages. FIG. 4 is a schematic diagram showing the relationship between the shape of a typical chopper mirror 11 and a light spot. If the spot diameter of the light is large, it takes a long time for the edge 11a to be exposed to the light when the chopper mirror 11 rotates. It can be said that the period in which the edge portion 11a crosses the light in this manner is a period in which the sample-side light beam Ls or the reference-side light beam Lr is not determined as the light beam sent to the entrance slit 14.

When the spot diameter of the light is large as in the conventional case, the detection signal obtained by the detector has a long period corresponding to the switching of both light fluxes as shown in FIG. Possible period is short. On the other hand, when the light spot diameter is reduced as in the device of the present invention, the detection signal obtained by the detector is swiftly switched between both light fluxes as shown in FIG. The possible period becomes longer. This means that the accumulation time of the received light signal becomes long, which is advantageous for improving the S / N ratio of the signal, and the analysis sensitivity and accuracy can be improved.

Another feature of this optical system is that in the measurement optical system A, the F number on the first light source 1 side of the sample side front optical system is "6" and the F number on the atomization part 8 side is " 8 "
The point is that the F number is increased on the exit side. In other words, this means that the optical system is a magnifying system and the efficiency of collecting light is enhanced. Conventionally, generally, the F-numbers on the light source side and the atomization section side of the sample side front optical system are the same.
On the other hand, in this device, the F number is increased on the exit side, so that the incident divergence angle of the light flux with respect to the optical axis is small on the exit side, that is, on the entrance side of the atomization section 8. As a result, light eclipse in the atomization section 8 is reduced, and the loss of light quantity is reduced.

By the way, according to the optical system of the atomic absorption spectrophotometer according to the present embodiment, with the above-mentioned configuration, it is possible to obtain a light amount more than twice as much as that of the conventional general apparatus by the detector. I was able to confirm.

The above embodiment is merely an example,
It is obvious that appropriate changes and modifications can be made within the scope of the present invention.

[Brief description of drawings]

FIG. 1 is an optical path configuration diagram excluding a photodetector of an atomic absorption spectrophotometer according to an embodiment of the present invention.

FIG. 2 is a diagram showing a result of calculating an image (ray trace) on a chopper mirror surface by a computer simulation by the optical system shown in FIG. 1 and an optical system of a conventional apparatus.

FIG. 3 is a schematic optical path configuration diagram of a double beam optical system in an atomic absorption spectrophotometer.

FIG. 4 is a schematic diagram showing the relationship between the shape of a chopper mirror and a light spot.

FIG. 5 is a diagram showing an example of a detection signal obtained by a detector.

[Explanation of symbols]

1 ... first light source 2 ... second light source 3 ... Half mirror 4 ... 1st toroidal mirror 5 ... 1st plane mirror 6 ... Second toroidal mirror 7 ... Second plane mirror 8 ... Atomization part 9 ... First concave spherical mirror 10 ... Third plane mirror 11 ... Chopper mirror 12 ... Fourth plane mirror 13 ... Second concave spherical mirror 14 ... Entrance slit 15 ... Concave spherical mirror 16 ... Planar diffraction grating 17 ... concave spherical mirror 18 ... Exit slit A ... Measuring optical system B ... Spectroscopic optical system

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akira Honda             1st Nishinokyo Kuwabara-cho, Nakagyo-ku, Kyoto City Stock Association             Inside the Shimadzu factory F-term (reference) 2G020 BA05 CA02 CB05 CB26 CB33                       CC48                 2G059 AA01 EE01 FF09 GG03 GG07                       JJ05 JJ14 JJ22 JJ24 LL02                       NN05

Claims (3)

[Claims] 1. A light beam emitted from a light source is split by a half mirror into a sample-side light beam and a reference-side light beam, the sample-side light beam is passed through an atomization section, and then both light beams are selected by a chopper mirror. In an atomic absorption spectrophotometer adapted to irradiate the entrance slit of the spectroscope, a sample through which a light beam on the sample side passes between the light source and the atomization part, and between the atomization part and the chopper mirror A side front optical system and a sample side rear optical system are respectively arranged, a reference side optical system through which a reference side luminous flux passes is arranged between the light source and the chopper mirror, and further between the chopper mirror and the entrance slit. A common optical system is arranged on the sample side light beam, and the sample side light beam is condensed on the atomization part by the sample side front optical system and then again condensed on the chopper mirror by the sample side rear optical system. Is the reference side optical system More focused on the chopper mirror, further atomic absorption spectrophotometer, characterized in that formed by focused on the entrance slit by both light beams are the common optical system. 2. The sample-side front optical system is characterized in that an F number directed to the atomization part side is set to be larger than an F number directed to the light source side.
Atomic absorption spectrophotometer described in. 3. The sample-side front optical system, the sample-side rear optical system, and the reference-side optical system are configured such that the converging magnifications of both light beams focused on the chopper mirror are substantially equal. The atomic absorption spectrophotometer according to claim 1 or 2, which is characterized.