JP2002228580A - Spectrophotometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spectrophotometer that has a sample chamber for reducing loss of luminous flux and preventing scattered light except from a sample. SOLUTION: A focus of an incident-side cylindrical lens 5 is set at an internal back end face 7T of an ultramicro cell 7 in a travel direction of a measuring luminous flux L, or at a termination of an optical path length CL. The measuring luminous flux L in the ultramicro cell 7 is thus sufficiently condensed, with the results that loss of the luminous flux can be reduced and scattered light except from the sample S can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectrophotometer for measuring an absorption spectrum of a measurement light beam passing through a sample to be measured and analyzing the sample.

[0002]

2. Description of the Related Art Conventionally, a spectrophotometer is provided with a sample chamber provided with a cell for accommodating a sample to be measured, and a measuring beam is passed through the cell in the sample chamber and its absorption spectrum is measured. Analysis.
In this case, it is required to measure a small amount of sample efficiently and with low noise by minimizing the energy loss of the measurement light beam.

First, a cell for filling the sample will be described. The cell includes a standard-sized cell used for measuring about 4 mL of a sample, an ultra-micro cell used for measuring about 50 μL of a very small sample, and 3 μL for example. There is a capillary cell and the like used for measuring a very small amount of sample. FIG. 5 shows a concept of an optical system which is a relation between these cells and a measurement light beam in the related art. That is,
A non-convergent optical system is used for a cell having a normal size as shown in FIG.
(B) A mask 8 for narrowing the luminous flux in the vertical direction as shown in FIG.
Is used, and the measurement light beam L is restricted by the mask 8 and enters the cell C. In addition,
The sample transmitted light beam LA in FIG. 5B shows a section of the focused measurement light beam.

FIG. 6 shows a sample chamber using a cell used for measuring a small amount of sample in a conventional spectrophotometer. In FIG. 6, on a base 1, an ultra-micro cell 7
Are fixed on the removable cell holder 2 as required. The cell holder 2 is provided with a mask 8 having an opening having a height of, for example, 1 mm as an aperture stop, so that only the parallel light flux near the optical axis of the measurement light flux L passes. CL is a distance in the ultra-micro cell 7 through which the measurement light beam L passes through the sample S in the sample chamber, and is called an optical path length.

FIG. 6B shows a cross section of the ultra-micro cell 7 viewed from the incident direction. A sample S is accommodated in a space in the ultra-micro cell 7. In order to reduce the amount of the sample S, the width of the portion holding the sample viewed from the incident light direction is limited to about 2 mm.

[0006] The sample chamber in the conventional spectrophotometer has the above configuration, and the entire unit of the measurement optical system having such a sample chamber is as shown in FIG. That is, lens holders 3 and 4 are fixed on the base 1 by fastening screws 3N and 4N, respectively. The lens holder 3 has a plano-convex incident side cylindrical lens 5 and the lens holder 4 has a plano-convex exit side. The cylindrical lenses 6 are mounted so as to have a curvature in the vertical direction and to be orthogonal to the measurement light beam L. The measurement light beam L enters the cylindrical lens 5 from the left side of the figure. In order to minimize the influence of spherical aberration, these two cylindrical lenses 5 and 6 are arranged oppositely so that a parallel light beam enters the convex side and exits from the convex side. An ultra-micro cell 7 is detachably mounted on the cell holder 2 between the incident side cylindrical lens 5 and the outgoing side cylindrical lens 6 when necessary. Note that B
F1 is the focal length of the incident side cylindrical lens 5, BF
Reference numeral 2 denotes a focal length of the exit-side cylindrical lens 6.

[0007]

The conventional spectrophotometer is as described above. In order to measure a small amount of sample S of, for example, 50 μL in such a conventional ultra-micro cell 7, the measurement light beam L must be measured. It is necessary to converge to about 1 mm in width and 1 mm in height. Therefore, in the conventional spectrophotometer, the width of the measurement light beam L is designed to converge to 1 mm or less, but the height of the measurement light beam L is 10 to 12 m.
m.
Before the measurement light beam L is incident on the mask, a mask 8 for setting the height (longitudinal) direction of the incident light to 1 mm is provided to cut the upper and lower portions of the measurement light beam L as shown in FIG. It is. In this case, since the upper and lower portions of the measuring light beam L having a height of about 10 to 12 mm are cut to extract only the measuring light beam L having a height of 1 mm at the central portion, the energy of the light incident on the sample chamber is reduced to 1/10 to 12 And only use one in one,
Not only is the amount of light wasted, but also in the case of measurement in the wavelength range of an ultraviolet light source whose energy is originally weak, there is a problem that noise increases.

In order to hold a further small amount of sample S,
For example, outer diameter 0.7mm, inner diameter 0.5mm, height 45mm
3 using a cylindrical capillary cell
When measuring a very small amount of sample S of about μL, a micropipette holder containing both a capillary cell made of quartz or the like and a small condensing lens arranged before and after the capillary cell is used. The measurement is enabled by replacing the standard cell with the standard cell. In this case, the optical path length of the measurement light beam L passing through the sample S is about 0.5 mm of the inner diameter of the capillary. Therefore, in order to convert the measured value to a value equivalent to the optical path length of 10 mm of the standard cell or the ultra-micro cell 7 for comparison with a general standard measured value, the measured value needs to be multiplied by 20. Errors are mixed because the energy is small. Therefore, the reproducibility is reduced as compared with the standard size cell and the ultra-micro cell.

FIG. 7 shows a simulation result by ray tracing in a sample chamber having such a conventional structure. In this simulation, the configuration of the unit shown in FIG. 8 was used as a model. That is, as shown in FIG.
Is located at the center of the microcell 7. In FIG. 7, the measurement light beam L is shown in black.

As shown in the simulation results,
At the rear end face inside the cell, the height of the measurement light beam L is expanded to 2.1 mm. Since the distance between the bottom surface of the ultra-micro cell and the lower surface of the measurement light beam L is usually limited to about 0.5 mm due to structural restrictions, when the height of the measurement light beam L expands to 2.1 mm, the distance of the measurement light beam L increases. Some are reflected on the bottom surface of the ultra-micro cell made of a different material from the sample, are detected as signals from the different material, and hinder measurement. The present invention seeks to provide a spectrophotometer that solves these problems.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the spectrophotometer provided by the present invention sets the focal point of the incident-side cylindrical lens at the terminal position of the optical path length of the cell in the traveling direction of the measurement light beam. It is set. By setting the focal point of the cylindrical lens on the incident side to the above-described position, it is possible to obtain a sufficiently narrowed measurement light beam in the section of the optical path length of the cell. Therefore, the conventional one-tenth
The light quantity that has been reduced to 1/12 can be reduced to about 1/3 to 1/4 within the measurement wavelength section, and the light quantity that is about 3 to 4 times that of the conventional case can be secured. It becomes possible.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a spectrophotometer provided by the present invention will be described below with reference to FIG. In FIG. 1, components indicated by the same reference numerals as those shown in FIGS. 6 to 8 are the same as the components shown in FIGS. 6 to 8, and a detailed description of these functions will be omitted.

In FIG. 1, a mask 8 is used as an aperture stop.
Is set to a height of 1 mm, and the center LC of the measurement light beam L
Is configured to pass only the measurement light flux near.
The standard length of the optical path length CL, which is the distance that the measurement light beam L passes through the sample S, is 10 mm. The optical path length CL is equal to the distance from the inner front end face 7S of the microcell 7 to the inner rear end face 7T.

In the above-described configuration, in the case of the present invention, the incident side cylindrical lens 5 is determined so that its focal point coincides with the inner rear end face 7T of the microcell 7, that is, the end of the optical path length CL. On the other hand, the exit-side cylindrical lens 6 is provided for the purpose of returning the divergent light after passing through the ultra-micro cell 7 to parallel light. In FIG. 1, the fixing position of the exit-side cylindrical lens 6 is symmetric with respect to the center of the ultra-micro cell 7 with respect to the entrance-side cylindrical lens 5, that is, the focal point of the exit-side cylindrical lens 6 is the inner front end of the ultra-micro cell 7. It is set to be located on the surface 7S.

The spectrophotometer provided by the present invention has the configuration as described above, and the simulation result in the embodiment of FIG. 1 is as shown in FIG. In other words, in a section where the optical path length CL is 10 mm, the height of the measurement light beam L is sufficiently narrowed to be a parallel light having a height of 1 mm. The simulation of this embodiment is an example in which the design wavelength is set to 200 nm. However, since the lens shows a dispersion phenomenon in which the refractive index changes according to the wavelength of the transmitted light, the focal length changes according to the wavelength. When the focal length changes in this manner, the light beam size at the inner rear end face 7T also changes. However, simulations show that 200 nm to 1100 n
As a result of verifying the luminous flux size with a spot diagram in the range of m, the luminous flux height increased by about 4% at a maximum of 1100 nm with respect to 200 nm, and this value does not pose a problem in practical use.

By using the above-described sample chamber according to the present invention, it is possible to measure a very small amount of sample S with an optical path length of 10 mm, which is most commonly used, without modifying the optical system of the spectrophotometer main body. It can be realized with low noise and good reproducibility, and the effect in practical use is very large. That is, the conventional 10
The amount of light that has been reduced from one-third to one-twelfth can be reduced to about one-third to one-fourth within the measurement wavelength section, and the light amount is about three to four times that of the conventional case. Can be secured. Assuming that the light quantity of the conventional 1/10 is improved to 1/3, (1/3) / (1/10) = 3.33.
In addition, since the central portion of the light speed having a height of 10 mm has a high energy, the light collection efficiency is increased to about four times when measured in the energy measurement mode of the spectrophotometer. The fixed position of the exit-side cylindrical lens 6 may be set to a fixed position such that the light beam size on the detector surface of the spectrophotometer main body is equivalent to a state where the sample chamber is not attached.

As described above, in the spectrophotometer provided by the present invention, the focal point of the incident side cylindrical lens 5 is set at the end of the optical path length CL of the ultra-micro cell 7 so that the luminous flux in the entire area of the ultra-micro cell 7 is sufficiently reduced. However, the present invention is not limited to the above and illustrated examples, and various modified embodiments utilizing the features of the present invention can be given.

For example, when dispersion of the lens becomes a problem, the wavelength region is divided into two portions, that is, a short wavelength side (200 to 350 nm) and a long wavelength side (350 to 1100 nm) in the ultraviolet region, and the incident side is divided. It is also possible to set two fixed positions of the cylindrical lens 5 and the exit-side cylindrical lens 6, and FIG. 2 shows this embodiment.

That is, FIG. 2A is a top view of the sample chamber,
FIG. 2B shows a side view of the sample chamber.
Reference pins P1, P2, P3, P4 for positioning the lens holders 3 and 4 at two prescribed positions, respectively.
Screw holes H1, H2, H3, and H4 for fastening the lens holders 3 and 4 to the base 1 are formed, and holes for fitting the reference pins P1 to P4 are formed in the lens holders 3 and 4, respectively. (Not shown) and a circular hole (not shown) that fits the screw holes H1 to H4. Therefore, in the measurement on the long wavelength side and the measurement on the short wavelength side, the positions of both lens holders 3 and 4 can be respectively changed. In FIG. 2, the positions on the short wavelength side of the lens holders 3 and 4 are indicated by solid lines, and the positions on the long wavelength side are indicated by dotted lines.

As another modified embodiment of the present invention, for example, when high-precision positioning is required so that dispersion of the lens becomes more problematic, the lens position can be set continuously variable as shown in FIG. , (B). FIG. 3A is a view of the sample chamber as viewed from above, and FIG. 3B shows only the cam plate 9 disposed below the base 1.

In this embodiment, the base 1 shown in FIG. 3 (a) is provided with a guide hole 1G, while the lens holders 3 and 4 are provided with engaging pins 10 and 11 implanted below. I have. At the point where the two arc-shaped guide holes 9G formed in the cam plate 9 intersect with the guide holes 1G of the base 1, the engaging pins 10 and 11 are connected to the two guide holes 1G and 9G.
Are engaged through. The cam plate 9 is disposed so that the lens holders 3 and 4 can reciprocate in the left-right direction in FIG. 3A by moving in the cam plate movement direction KS shown in FIG. 3B. The amount of movement of the cam plate 9 corresponds to the change in focal length due to the dispersion of the lens used. Further, by connecting the cam plate 9 to an endless belt and finely driving the endless belt in the direction of arrow KS by driving a stepping motor, the lens position can be mechanically adjusted according to the wavelength shift of the main body of the spectrophotometer. You can also The present invention includes all of these modified embodiments.

[0022]

Since the present invention has been described in detail above, it is possible to measure a small amount of a sample satisfactorily without modifying the optical system of the main body of the spectrophotometer and using the optical path length of a normally used cell. Can be. Further, noise can be reduced and reproducibility can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical system unit of a spectrophotometer according to the present invention.

2A and 2B are views showing a modified embodiment of the present invention, wherein FIG. 2A is a top view and FIG. 2B is a side view.

FIGS. 3A and 3B are views showing another modified embodiment of the present invention, wherein FIG. 3A is a top view thereof and FIG. 3B is a view showing a cam plate.

FIG. 4 is a diagram showing a result of a simulation of an example according to the present invention.

5A is a diagram showing a concept of a relation between a cell having a standard size and a measurement light beam, and FIG.

FIG. 6 is a diagram showing a conventional technique.

FIG. 7 is a diagram showing a result of a simulation in a conventional spectrophotometer.

FIG. 8 is a diagram showing a configuration of an optical system unit in a conventional spectrophotometer used as a simulation model by ray tracing.

[Explanation of symbols]

 2: Cell holder 3, 4: Lens holder CL: Optical path length 5: Incident-side cylindrical lens 7: Ultra-micro cell 7S: Inside front end face 7T: Inside rear end face 8: Mask S: Sample 9: Cam plate

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G020 AA03 AA04 AA05 BA14 CA02 CB04 CB07 CD03 CD13 2G057 AA01 AB01 AB02 AB03 AB06 AC01 BA03 2G059 BB04 DD13 EE01 EE12 HH01 HH02 HH03 JJ11 JJ30 LL01 LL02

Claims (3)

[Claims] An incident-side cylindrical lens for converging a measurement light beam incident parallel to the optical axis on the optical axis, an aperture stop for passing only a portion of the converged measurement light beam near an optical axis close to the parallel light beam, and an aperture. An emission-side cylindrical lens for returning the light beam that has passed through the aperture to the original parallel light beam, and a cell that is arranged on the optical axis between the two cylindrical lenses and that accommodates the sample to be measured, and has an absorption spectrum of the sample in the cell. Wherein the focal point of the incident-side cylindrical lens is set at the end position of the optical path length of the cell in the traveling direction of the measurement light beam. 2. The spectrophotometer according to claim 1, wherein the cell comprises an ultra-micro cell for measuring a small amount of a sample to be measured. 3. The spectrophotometer according to claim 1, wherein the cell is constituted by a capillary cell for measuring a very small amount of a sample to be measured.