JPH0274847A - Method and jig for measuring infrared absorption spectrum by diffusion reflection method - Google Patents

Abstract

PURPOSE:To make it possible to measure infrared-ray absorption at high sensitivity by using a minute amount of specimen by mounting a minute powder specimen on a measuring jig having a mirror surface at an infrared-ray reflecting surface, condensing and projecting the infrared rays which are emitted from an infrared-ray source part, and measuring the infrared-ray absorbing spectrum of the specimen. CONSTITUTION:Infrared rays emitted from an infrared-ray source part 7 are reflected from reflecting mirrors 1 and 2 and condensed with a concave mirror 3. The infrared rays are projected toward a specimen which is directly mounted on a horizontal mounting surface 10 of the mirror surface at the center of a measuring jig 8. The diffused light from the specimen is condensed with a concave mirror 4 again and guided to a detecting system 9 with reflecting mirrors 5 and 6. Even the minute amount of the specimen can be measured. A minute absorbing peak can be emphasized and detected. Since it is not necessary to dilute the specimen with powder, pretreatment such as adjustment of the specimen can be omitted.

Description

[Detailed description of the invention] (a) Industrial application field This invention relates to an infrared absorption spectrometry method using a diffuse reflection method, and is particularly used for high-sensitivity qualitative analysis of powder samples of organic and inorganic compounds in general. .

(b) Conventional technology Conventionally, the method used to measure the infrared absorption spectrum of powder samples, whether organic or inorganic, is to knead them into a liquid substance with low infrared absorption, such as aliphatic hydrocarbons. However, it could not be used to measure areas where absorption spectra overlap, minute changes, or minute peaks.

In place of this, the following two methods have been developed. Namely, i) a method in which the sample is diluted with potassium bromide (hereinafter referred to as KBr) powder, pressure-molded into a pellet shape, and measured using a transmission method, and ii) a method in which the strong regular reflection light reflected from the sample surface is used. In this method, the sample is diluted with KBr powder or the like in order to remove it, and then measured using the diffuse reflection method. Among these methods, the diffuse reflection method focuses infrared radiation from an infrared light source onto the sample from one direction, and after repeating reflection and transmission within the sample, this irradiated light is diffused from the sample over the entire solid angle. This is a method of measuring infrared absorption by a sample by comparing it with the diffuse reflection spectrum. In general, infrared absorption measurement of powder samples using the diffuse reflection method in 11) is simpler and does not require the effort of pressure molding the sample compared to method i) above, but in addition to the fact that the diffuse reflection light is very weak. Although the influence of the strong specularly reflected light reflected from the sample surface can be suppressed to some extent by sufficiently diluting it with KBr powder, etc., it cannot be completely eliminated, so the relationship between the spectral intensity and the sample amount is The problem is that the linearity between the two is often impaired, and quantitative analysis is accompanied by various difficulties. In other words, the transmission method is generally more direct for quantitative analysis, and when discussing the regularity of the diffuse reflection method, it is important to consider sample preparation such as KBr dilution as described above, and measurements such as the specular reflection method. Even if the above precautions are taken into account, there is still a problem with large uncertainties.

(c) Problems to be solved by the invention However, none of the above-mentioned conventional measurement methods is a high-sensitivity measurement in the principle sense, and the sample is measured as it is by the diffuse reflection method without using a diluent such as KBr. However, high-sensitivity qualitative analysis was not possible because the diffuse reflection light from the sample was weak and the strong specular reflection reflected from the sample surface.

In addition, in both methods i) and ii), it is virtually impossible to collect the sample to be measured because it is mixed with and diluted with KBr powder. In addition, sample preparation is complicated and must be uniformly mixed into KBr powder, so it is generally difficult to detect heavy samples if they are less than a few milligrams, and KBr powder requires hundreds of milligrams. This also becomes a burden in terms of running costs. Furthermore, it goes without saying that it cannot be used for substances that chemically react with KBr, but the influence of the material of the mortar used for crushing cannot be ignored. This becomes more serious as the measured spectral intensity of the sample itself or the substance contained in the sample becomes weaker. On the other hand, KBr is a highly hygroscopic substance, and water has a very strong absorption band in a fairly wide range of infrared absorption measurement, so it is often difficult to identify the substance depending on the measurement conditions. there were. In order to avoid the problem of hygroscopicity, diamond powder, which is relatively transparent to infrared light, is sometimes used instead of KBr powder to make a diluted powder sample, but this is not common due to cost and handling problems. .

In addition, in the diffuse reflection method (ii), the flatness of the KBr powder sample surface is often a problem, and the optical path adjustment of the infrared light is slightly deviated due to the difference in flatness with the mirror for adjusting the optical system. It is not necessarily easy as it requires fine preparation.

Therefore, compared to conventional methods, this invention utilizes an infrared absorption method using a diffuse reflection method that essentially enables more sensitive infrared absorption measurement with a smaller amount of sample without adjusting the sample with a diluent such as KBr powder. This project aims to create and provide an absorption spectrum measurement method.

(d) Means for Solving the Problems This invention enables high-sensitivity measurement of infrared absorption spectra of powder samples without using the dilution method with KBr powder used in the conventional diffuse reflection method. Diffusion is characterized in that a fine powder sample is placed on a measurement jig with a mirror surface, and the infrared absorption spectrum of the sample is measured by condensing and irradiating infrared light emitted from an infrared light source. This provides an infrared absorption spectrum measurement method using a reflection method.

In this invention, the sample holder has a horizontal mounting surface on which a powder sample can be placed in the center and has a shape that can be installed in the diffuse reflection optical system of an infrared absorption spectrum measuring device, A jig for measuring infrared absorption spectra using a diffuse reflection method is used, which is characterized in that the mounting surface is a mirror surface. For example, FIGS. 2 to 7 show measurement jigs (sample holders) for performing measurements provided by the present invention. These measuring jigs 8 have a mirror horizontal mounting surface lO on which a sample is mounted on an infrared light reflecting surface, and for example, a fourth
As shown in the figure, it has a parallel plate shape and may have a mirror surface on the entire surface from the center to the periphery, but it is more efficient to have a mirror surface only on the part where the infrared light beam is focused. For example, as shown in FIGS. 2 and 3, it is preferable to form a mirror-like horizontal mounting surface IO on a convex top surface or a concave bottom surface at the center. This is because unnecessary reflected light can be removed as much as possible. The external shape of the measurement jig 8,
The dimensions are arbitrary as long as they do not interfere with operation.

The external shape of the mirror horizontal mounting surface 10 depends on the infrared beam diameter of the infrared spectrophotometer used and the light-gathering ability of the diffuse reflection optical system, but a diameter of several millimeters is sufficient.

Note that the measuring jig 8 may be made of any material as long as it is mirror-finished and reflects infrared light, but stainless steel, for example, is preferable in consideration of durability. As shown in detail in Figures 2 to 7, it is better for the central horizontal mounting surface 10 to have a different infrared light reflectance and shape than the peripheral parts, and to prevent excess light from the peripheral parts. It is important to have an optical structure that can remove reflected light as much as possible. This central mirror surface part may be formed integrally with the measuring jig as shown in Fig. 7, but it can be attached to the measuring jig by screwing it as shown in Fig. 5 or by fitting it as shown in Fig. 6. It may be possible to separate it from the periphery.

Although the sample is placed on a mirror surface, by using the jig of the present invention, both optical system adjustment and infrared absorption measurement can be performed using the same optical system without adjustment. This is inevitable in principle in the conventional diffuse reflection method. The thickness of the sample to be measured by this invention is several 10 to several 100.
Since it is less than μm, such a situation does not occur, and there is no need to readjust the optical system even if the measurement sample is replaced.

The measurement jig 8 shown in FIGS. 2 to 7 is used by being mounted at a position facing the concave mirror 3.degree. 4 in the diffuse reflection optical system, as shown in FIG. In FIG. 1, the direction of infrared light emitted from an infrared light source 7 is changed by plane mirrors 1 and 2, and condensed by a concave mirror 3 at the sample position of a measurement jig 8, and the infrared light is diffusely reflected from the sample. External light is collected by a concave mirror 4, reflected by a reflecting mirror 5.6, and guided to a detection system 9.

Here, the optical path when the infrared light focused on the sample is diffusely reflected by the sample will be explained in detail.

Infrared light (A) reaching the sample as shown in Figure 8
A part of the light becomes specularly reflected light (B), but the rest becomes light incident on the sample (C) (C'). Here, the incident light (C) shows a diffusion process of infrared light in a wavelength range where total absorption is large because the absorption coefficient is large.

Due to the large absorption, the effective penetration depth of infrared light is several micrometers compared to the sample size, for example, several tens to hundreds of micrometers.
It is small, around m, so it does not depend on the sample size.

On the other hand, the incident light (C') shows the diffusion process of infrared light of a wavelength with small total absorption by the sample to be measured. This is important, for example, when dealing with characteristic absorption lines with low content in the case of mixtures and small absorption coefficients in the case of pure substances. Since the total absorption is small, the material is diffused, reflected, and transmitted many times within the sample, so the effective measured film thickness is sufficiently large compared to the sample size. In any case, after interacting with the sample, infrared light (D
) is condensed together with the specularly reflected light (B) and reaches the detection system.

In the latter of the above two cases, that is, the characteristic vibration peak of a low concentration impurity or additive, or a molecule, atomic group, or ion with a small absorption coefficient, the more effective this invention becomes. become. In other words, since the effective film thickness is much larger than the sample size, essentially highly sensitive measurements are possible.

The optical system for the diffuse reflection method of this invention can be sufficiently used as long as it has a light-gathering ability of about 4 to 8 times and a photometric solid angle of about π steradian, and the detector is a thermocouple type, Any type, such as a pyroelectric type or a semiconductor type, can be used.

Among these, the semiconductor type is particularly preferred because it has high sensitivity and allows the present invention to be utilized more effectively.

(e) Effect For example, when dealing with characteristic absorption lines that have a low content in the case of a mixture or a small absorption coefficient in the case of a pure substance, infrared light in these wavelength ranges has a small total absorption. Because it is repeatedly diffused, reflected, and transmitted many times within the sample or on the mirror surface of the measurement jig of this invention, the effective measurement film thickness is sufficiently large compared to the sample size, and weak absorption peaks are emphasized. Strong absorption peaks are compressed.

(f) Embodiment An embodiment of the present invention will be explained with reference to FIG. 1 again. The infrared light emitted from the infrared light source section 7 is reflected by the reflection 11.2, and condensed six times by the concave mirror 3.The infrared light emitted from the infrared light source section 7 is then condensed six times by the concave mirror 3. Irradiation is directed toward a 30μ9 sample (polymethyl methacrylate) placed directly on the placement surface IO.

The diffused light emitted from the sample is again focused by a concave mirror 4 having a photometric solid angle of π steradians, and guided to a detection system 9 by a 5.6-inch reflecting mirror. If this arrangement and measurement jig 8 are used, the same reflective surface can be used for the horizontal mounting surface lO and the optical system adjustment mirror, so readjustment is not necessary as described above.

FIG. 9 shows the infrared absorption results of polymethyl methacrylate obtained as described above.

Fig. 11 shows the red color of each polymethyl methacrylate obtained by the transmission method using the KBr compression molded body in i) above, and Fig. 1O shows the red color of each polymethyl methacrylate obtained by the diffuse reflection method using the KBr powder dilution method in 11) above. The external absorption results are shown as a comparative example. As is clear from comparing the three types of spectra above, even if the method of this example is used, Comparative Example 1) ii)
It goes without saying that a spectrum similar to that obtained by the method described above can be obtained, but it is also possible to obtain minute absorption beams such as the overtone peaks of carbonyl groups as shown by A, B, and C in Figure 9 of the example. Although it was difficult to measure by the method of Comparative Example 1) ii), it was found that it could be observed very clearly and clearly in this example. In addition, in the conventional diffuse reflection method using KBr dilution in 11), the effect of water in KBr is seen, although it is slight, and it takes a considerable amount of time to remove this effect.
In the method according to this embodiment shown in the figure, since KBr, which causes hygroscopicity, is not used, no influence of moisture is observed and such waiting time is unnecessary.

Table 1 shows the minimum amount of sample required for each of the above measurement methods, using polymethyl methacrylate as an example.

It can be seen from Table 1 that the amount of sample required for measurement in this example is extremely small compared to the transmission method and the conventional diffuse reflection method. The features of the present invention, such as high-sensitivity measurement and ultra-fine measurement, and their effectiveness have been fully demonstrated.

Examples of measurement jigs for the purpose of making measurements according to the present invention easier are shown in Figures 2 to 7. It is necessary to do so. Although five examples are given in this figure, if the horizontal mounting surface 10 is a mirror surface and promotes specular reflection, the shape of the peripheral portion is not specified. but,
Any geometrical or optical structure must function to reduce the effects of specular reflection from the periphery.

(G) Effects of the Invention According to this invention, firstly, it is possible to measure even a minute amount of sample, for example, 1 microgram or less, and secondly, it is possible to emphasize minute absorption peaks that were previously difficult to detect. Thirdly, since there is no need to dilute with KBr powder, pretreatment such as sample preparation can be omitted, which not only shortens the measurement time but also eliminates the influence of KBr's hygroscopicity. This is a special polymer material that can improve the detection ability of minute absorptions and makes it easy to collect the sample to be measured. It is possible to provide an infrared absorption spectrum measurement method using a diffuse reflection method that can easily obtain infrared absorption spectra such as the following.

[Brief explanation of the drawing]

Fig. 1 is a diagram of a diffuse reflection optical system used in an embodiment of the present invention, and Figs. 2 to 7 are a perspective view and a cross section of a measuring jig for carrying out the measurement method of the present invention more easily. Figure 8 is an explanatory diagram of the diffuse reflection process of irradiated infrared light within the sample, Figure 9 is a diagram of the infrared absorption spectrum of polymethyl methacrylate powder obtained in an example of the present invention, and Figure 10 11 is an infrared absorption spectrum diagram of polymethyl methacrylate powder obtained by a conventional method. 1.2, 5.6...Reflector, γ rod diagram...Concave mirror,...Infrared light source,...Measurement jig (sample holder), -Detection system,... ...Mirror horizontal mounting surface. Red Tato Yudai

Claims (1)

[Claims] 1. A fine powder sample is placed on a measuring jig having a mirror surface on its infrared light reflecting surface, and the sample is irradiated with focused infrared light emitted from an infrared light source. An infrared absorption spectrum measurement method using the diffuse reflection method, which is characterized by measuring an infrared absorption spectrum. 2. A sample holder having a horizontal mounting surface on which a powder sample can be placed in the center and having a shape that can be installed in the diffuse reflection optical system of an infrared absorption spectrum measuring device, and at least the horizontal mounting surface is A jig for measuring infrared absorption spectra using a diffuse reflection method, characterized by being composed of a mirror surface.