JPH01136049A - Absorbance measurement - Google Patents

Abstract

PURPOSE:To achieve accurate measurement of absorbance without being affected by contamination and aging, by a method wherein light within a certain wavelength range is swung cyclically centered on a specified wavelength to irradiate an object to be inspected within a cell and the light transmitted through the object being inspected is received with a light receiving element. CONSTITUTION:An adjusting screw 18 and an adjusting member 19 are previously regulated to vary the direction of a prism 8 beforehand so that light with a wavelength absorbable by an object 9 to be measured centers with respect to a light beam from a collimator 7. Thereafter, a scanning motor 13 is driven to turn the prism 8 so that light swings cyclically centered on a specified wavelength allowing transmission through the object being inspected within a cell 9. Thus, a light receiving element 12 can receive light with a wavelength within a certain range centered on the specified wavelength, thereby permitting of an absorbance of the object being inspected with electric processing of the light reception signal.

Description

[Detailed Description of the Invention] [Field of Industrial Application] ' The present invention is a method for measuring the absorbance of liquids, gases, solids, powders, etc. Regarding methods of measuring etc.

[Conventional technology and its problems]

One of the conventional absorbance measurement methods described above is a measurement method using a single beam.

In this measurement method, the analyte, which is a fluid in a cell, is irradiated with spectroscopic light, and the concentration of the analyte is measured from the intensity of the transmitted light that has passed through the analyte. There have been problems with poor light sources, dirt and aging of the prisms and gratings that make up the monochrome system, and dirt on the cell in which the subject is placed, which directly affects the measured values, making accurate measurements impossible.

Therefore, there is a double beam measurement method that solves the problems of the single beam measurement method described above. This measurement method irradiates separated light into both the cell containing the sample subject and the cell containing the standard sample, and measures the concentration by comparing the transmitted light from each cell. be. This method does not suffer from the disadvantages of the single-beam measurement method described above, such as deterioration of the light source, dirt on the prisms and gratings that make up the monochrome system, and deterioration over time.
However, differences in contamination between the cell that holds the sample and the cell that holds the standard and semi-standard substances cause errors in the measured values, and the sensor's light-receiving surface has uneven sensitivity, so it is exposed to light from two directions. There is a problem in that when the light is irradiated, a sensitivity difference occurs in the received light output, and the error caused by this cannot be ignored.

Furthermore, as a method to solve this problem, there is a method using two interference filters, which is an improvement on the single beam measurement method. This is a method in which filters with wavelengths that are absorbed by the subject in the cell and filters with wavelengths that are not absorbed are alternately placed on the optical path, and the transmitted light of each is compared and measured.

According to this method, since the light that has passed through the object is compared with the light that has not passed through the object, cell contamination can be ignored. Although this can be solved, there is a problem in that the filter must be replaced every time the absorbance of a different subject is measured, and the wavelength of light cannot be finely adjusted to suit the subject.

[Means for solving problems]

The present invention solves the above-mentioned problems such as deterioration of the light source, monochrome stains, aging, and stains on the subject (for example,
The absorbance can be measured accurately because the wavelength absorbed by the sample can be easily fine-tuned without being affected by cell contamination (cell contamination), and it changes continuously if the sample has a similar composition. The method is to irradiate the object with light from a light source through a monochrome system such as a prism or grating, and measure the amount of light that is transmitted or reflected through the object. In a method of measuring the absorbance of a subject by receiving light from the light source, at least one specific wavelength of light that is absorbed by the subject is selected from a spectrum obtained from the light source through a slit, and the selected specific wavelength is This is done by a method of measuring absorbance in which the subject is irradiated with light having a wavelength range that is absorbed by the subject, centered around .

[For production]

In the absorbance measurement method of the present invention, light from a light source is passed through a prism,
When irradiating a subject through a monochromatic system such as a grating, means is provided for selecting a specific part of the subject that the subject absorbs in the middle of the monochrome system, and this means is driven to By irradiating the subject with light in a wavelength range that is periodically swung around the specific wavelength, and receiving the light that is transmitted through or reflected by the subject with a light receiving element, This is to obtain a symmetrical signal.

[Embodiments of the invention]

Hereinafter, an example of an apparatus for carrying out the absorbance measurement method of the present invention will be described with reference to the drawings.

In Fig. 1, 1 is the amount of light, 2 is a condensing mirror that condenses the light from the light source, and β is a mirror that reflects the light from a collimator 7, which will be described later. 4 is a disk having a large number of slits formed on its outer periphery, and a chopper motor 5 modulates the light passing through the condensing mirror 2 to 1Klz. 6 is a slit plate that limits the light from the slit of the disk 4 to a certain width and extracts the separated light; 7 is a collimator that reflects the light from the slit plate 6 as parallel light; 8 is the collimator 7 It refracts and reflects light of a specific wavelength out of the light, and the specific wavelength can be varied by a scanning means to be described later,
and a prism that vibrates in a certain wavelength range centered on the specific wavelength, 9 is the prism 8, the collimator 7,
It is a flow-type cell that is irradiated with light reflected through a slit plate 6 and a mirror 3, and contains a subject to be measured inside. 10 is a mirror that reflects the light transmitted through the cell 9, 11 is a condensing mirror that condenses the light from the mirror 10, and 12 is a light receiving element disposed at the focal point of the condensing mirror 11. Note that the slit plate 6 is the condensing mirror 2
The length of the slit is determined so that the light from the collimator 7 does not overlap with the light from the collimator 7.

According to the monochrome system described above, the light from the light source 1 is transmitted through the condensing mirror 2 -> the slit of the disk 4 -> the slit of the slit plate 6 - the collimator 7 -> the prism 8 - the collimator 7 - the slit of the slit plate 6 - the mirror. 3→object in cell 9-mirror lO→light is irradiated onto the light receiving element 12 via the condensing mirror 11, so the absorbance of the object can be measured from the amount of light received.

However, the above-described apparatus suffers from the same drawbacks as the conventional single beam system.

Therefore, in the present invention, the problems in the prior art are solved by providing a scanning means that vibrates the refracted and reflected light from the prism 8 in a certain wavelength range centered around a specific wavelength.

That is, the scanning means is the scanning motor 13.
, a cam 15 rotated by the scanning motor 13 via a belt 14, and a roller 16a attached to the cam 15.
and a substantially U-shaped first arm 16 in which the first arm 16 is fixed in a position adjustable manner by two screws 17a and rotatably supported by a shaft portion 17b. a second arm 17; an adjustment screw 18 which is screwed onto one side of the second arm 17 and whose tip abuts the tip of the first arm 16; and an adjustment screw 18 which is attached to the other side of the second arm 17 and is The adjusting member 19 whose distal end abuts the distal end of the screw 19a and the pivot fulcrum 20a at the base end are rotatably supported by a shaft, and the pivot fulcrum 2
The prism 8 is a rotating arm on which the prism 8 is fixed, and the tip thereof is always spring-biased by a spring 21 toward the adjustment member 19 side.

When the scanning motor 13 is rotated, the cam 15 is rotated via the belt 14.
The first arm 16 is displaced via the roller 16a that is in contact with the roller 16a. When the first arm 16 is rotated, the second arm 17 fixed to the first arm 16 by a screw 17a
is rotated about the shaft portion 17b as a fulcrum, so that the adjustment member 1
9, the rotating arm 20 is rotated about a rotating fulcrum 20a. Therefore, the rotation fulcrum 20 of the rotation arm 20
The prism 8 fixed at point a vibrates at a rotation angle corresponding to the shape of the cam 15.

Note that when changing the direction of the prism 8, use the screw 17a.
Loosen the adjustment screw 18 and adjust the first and second arms 16.
．． This can be done by shifting the relative positions of 17. In addition, when changing the selected wavelength width, the adjusting member 19
This can be done by adjusting the screw 19a.

In this way, adjust the adjustment screw 18 and adjustment member 19,
The direction of the prism 8 is changed in advance with respect to the light beam from the collimator 7 so that the light of a wavelength that can be absorbed by the subject to be measured is centered, and then the scanning motor 13
By driving the prism 8, the prism 8 rotates, and therefore periodically vibrates around light of a specific wavelength that can pass through the subject in the cell 9. Therefore, since the light-receiving element 12 receives light within a certain range of wavelengths centered around a specific wavelength, the absorbance of the subject can be measured by electrically processing the light-receiving signal.

Furthermore, to explain in detail, the rotation angle θ of the cam 15 is determined as shown in FIG.
As shown in FIG. 2(b), it depends on the displacement ΔX of the first and second arms 16 and 17 for rotating the prism 8, and furthermore, the displacement ΔX depends on the rotation angle δ of the prism 8 as shown in FIG. 2(b). linearly dependent. Also, this rotation angle δ is shown in Fig. 2(e).
As shown in (-In order to determine the selected wavelength λ of the incident light, the rotation angle e of the cam 8 determines the selected wavelength λ.

Note that if the shape of the cam 8 used is circularly eccentric, the relationship between the moving distance and time is represented by an approximately parabola as shown by the solid line in FIG. Figure (a
) It can be used as an antilog scale, which allows moving distance to be measured linearly with respect to time, as shown by the broken line.

When the cam 8 is rotated, as shown in FIG. 2(d), the fluctuation range of the wavelength λ becomes λa-λC-λa when it rotates once as θB −x □ c−θa. Therefore, the wavelength λ
If the subject in the cell 9 absorbs light due to a change in It is something.

Next, a circuit for detecting absorbance from the output signal obtained from the light receiving element 12 will be explained with reference to FIGS. 3 and 4. , FIG. 3 is a block diagram, 12 is the above-mentioned light receiving element,
For example, a photocell. 22 is an amplifier that amplifies the output from the light receiving element 12, 23 is a rectifier circuit that half-wave rectifies the AC signal from the amplifier 22, and 24 is the rectifier circuit 23.
A smoothing circuit 25 demodulates the signal from the smoothing circuit 24.
26 is the differentiation circuit 25 for differentiating the signal of
27 is a gate circuit that opens a gate in response to a zero-cross signal from the zero-cross detection circuit 26 and allows the signal from the smoothing circuit 24 to pass through; 28 is a gate circuit 27; If the voltage signal outputted from in (Eb
/Eo); 29 is a calculation circuit that calculates Eo = (Ea +Ec)/2 when the voltage signal output from the gate circuit is as shown in FIG. j! from the voltage signal Eo from the circuit 29 and the voltage signal Eb from the gate circuit 27! n (
This is a logarithmic circuit that calculates Eb/Eo). and,
The logarithm circuits 28 and 30 each output a value of (-KW). Here, K is the extinction coefficient of the analyte in the cell 9,
W is the thickness of the cell 9.

Next, the operation will be explained based on the block circuit diagram of FIG. 3 mentioned above and the waveform diagram of FIG. 4.

First, the light receiving element 12 sends out an output signal as shown in FIG. It is half-wave rectified by Fig. 4 (
An output signal as shown in b) is obtained, and further demodulated by the smoothing circuit 24, an output signal as shown in FIG. 4 [C] is obtained. Then, when the output signal from the smoothing circuit 24 is differentiated by the differentiating circuit 25, an output signal as shown in FIG. Ea and Eb in FIG. 4(C) are obtained by opening the gate of the circuit 27.

Obtain the voltage signal of Ec.

Here, the voltage signal from the gate circuit 27 is shown in FIG.
C), Ea - Ec = Eo (Eo is the output from the light receiving element 12 when the absorption of the object is set to zero.

). That is, it is possible to obtain a symmetrical signal with λC as the center line. Here, λb means the absorption wavelength of the subject. From the above, the light absorbance A is calculated by the logarithmic circuit 28, and A = 7! n (Eb/Eo) --
-(1) - Expressed as -. Also, the absorption of the analyte is E
b = Eo exp (KW) ・−・−t2)
Here, K is the extinction coefficient of the subject, and W is the shape coefficient of the cell 9.

Then, by substituting the above (2) 2 into equation (1), A=1
n (Eb/Eo) = in (Bo exp (KW) / Eo
]-”13), so EO is deleted from equation (3) and A=fnexp(-KW)=-KW...
・The following relationship (4) is obtained, and the absorbance can be obtained.

In addition, in the measurement described above, the amount of light from the light source l is constant,
The explanation is based on the case where the output signal from the light receiving element 12 is constant with respect to the wavelength λ as shown in FIG. The output signal is as shown in FIG. 4(e). In this case, the waveform shown in FIG. 4(e) is differentiated by the differentiating circuit 25 (FIG. 4(f)), the zero-crossing point is determined by the zero-crossing detection circuit 26, and the Eo point is determined by the arithmetic circuit 29.

Eo = (Ea + Ec) / 2 -...
(5) The absorbance A can be determined by inputting the voltage signal Eo obtained in this manner to the logarithmic circuit 30 together with the voltage signal Eb from the gate circuit 27 in the same manner as described above.

That is, the output Ea at wavelength λa, the absorption wavelength λb of the object
By determining the output Eb, it is possible to determine the absorbance of the subject regardless of the performance of the light source l.
゛As described above, the prism 8 is swung around the wavelength λb that is absorbed by the subject whose absorbance is to be determined.
By adjusting the adjustment screw 18 and the adjustment member 19, one rotation of the cam 15 will yield a wavelength in the applicable range of λa - λc - λa. Therefore, by performing the same calculation as described above, the absorbance of the subject is determined. It is something that can be done.

Furthermore, when the prism 8 is swung greatly, several wavelengths λb that can be absorbed by the subject appear, and the above-described operation is performed to select one of them and oscillate around the selected wavelength λb. All you have to do is perform the measurement.

Note that in the above embodiments, the case of a test object through which light passes, such as a fluid, was explained; however, in the case of a test object through which light does not pass, that is, in the case of a solid or powder, the object may be irradiated. By receiving the reflected light with the light receiving element 12, the absorbance of the subject can be measured. Also,
In the above embodiment, the absorbance was measured with the sample placed in the cell 9, but by passing the sample continuously through the cell 9, samples with the same composition The absorbance of the analyte can also be measured continuously. Furthermore, by passing light through a thin film such as photographic film and measuring the absorbance (-KW) of the film, the thickness of the film can also be determined.

Furthermore, in the embodiment described above, the light from the mirror 3 is irradiated onto the subject in the cell 9, and the light transmitted through the cell 9 is received by the light receiving element 12 via the mirror 10 and the condensing mirror 11. Although the light from the mirror 3 is irradiated onto the subject via an optical fiber, the transmitted light or reflected light from the subject may be received by the light receiving element 12 via the same optical fiber. .

In addition, in the above-mentioned embodiment, the absorbance of a specific object is measured, but if the prism 8 is swung over a wide range by the cam 15 and the cell 9 is irradiated with light of all wavelengths from the light source 1, the absorbance of a specific object is measured. By detecting light at a wavelength that is absorbed by the subject, the components of the subject can also be determined.

〔Effect of the invention〕

As described above, the present invention includes periodically oscillating light in a certain wavelength range centered on a specific wavelength, irradiating the subject in the cell, and receiving the light transmitted through the subject by a light receiving element. Because it is possible to measure the absorbance of the sample, even with the single beam method, which has a very simple structure and can be manufactured at low cost, it is not affected by poor light source, monochrome dirt, aging, and cell dirt. In addition, since the specific wavelength can be freely selected and obtained with high accuracy, it is possible to select and irradiate light at the wavelength that the subject absorbs the most, and therefore, accurate absorbance can be measured. In addition, this method has the advantage that the absorbance of a sample having a similar composition can be measured continuously.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a structure for carrying out the absorbance measurement method according to the present invention, FIG. 2 is an explanatory diagram for explaining the main parts of the same, and FIG. FIG. 4 is an output waveform diagram for each of the above block diagrams. 1... Light source, 6... Slit, 8... Prism,
9... Cell, 12... Light receiving element, 15 River cam. Patent Applicant: Saginomiya Seisakusho Co., Ltd. ψA1 Tokaku e No. 20 (a) (b) (c) (e) No. 40

Claims (1)

[Claims] In a method of measuring the absorbance of a subject by irradiating light from a light source onto a subject through a monochrome system such as a prism or grating, and receiving the amount of light obtained by transmitting or reflecting the subject with a light receiving element. , select at least one specific wavelength of light that is absorbed by the subject from the spectrum obtained from the light source through the slit, and select light with a wavelength width that is absorbed by the subject with the selected specific wavelength as the center. A method for measuring absorbance characterized by irradiating a subject with periodic shaking.