JPH03282352A - Signal detector for optoacoustic infrared spectrochemical analysis - Google Patents

Abstract

PURPOSE:To allow the measurement of a very small black sample or spherical (or particulate) sample which is difficult to be measured by obtaining the optoacoustic IR spectra corresponding to IR absorption spectra. CONSTITUTION:The sample is irradiated with the modulating IR light 1 stopped down by a condenser mirror 3 via a crystal plate 11 and the optoacoustic IR signal generated from the microsample (a) is detected by a high-sensitivity microphone 12 and is amplified by a preamplifier 13; thereafter, the signal is sent to a data processor 16. A piston 14 is moved by a step motor 15 and the volume in the hermetic space in a detector is gradually changed. The optoacoustic IR signal of the preamplifier 13 is fed back to a data processor 16 at all times so as to determine the position where the optoacoustic signal generated from the sample is increased by a resonance phenomenon. The pres sure in the detector S is monitored at all times by a pressure sensor built in a valve 20. The piston 14 is changed and the optoacoustic signal is subjected to Fourier transform by the data processor 16 in the position where the optoacoustic signal detected by the high-sensitivity microphone 12 is maximized. by which the optoacoustic IR spectra are obtd.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Field of Application) The present invention provides a photoacoustic infrared spectrum (FTIR/P
The present invention relates to a signal detection device for photoacoustic infrared spectroscopy for determining A spectrum).

(Prior art) In recent years, Fourier transform type micro infrared spectrometers (micro FT-IR), which incorporate a microscope mechanism, have come to be used to analyze minute samples (particularly organic compounds). ,
In some cases, it has become possible to obtain infrared absorption spectra even for microscopic samples of several micrometers. However, in the case of a black sample, the modulated infrared light irradiated is absorbed and becomes difficult to transmit, and in the case of a spherical (or particulate) sample, the transmitted infrared light is refracted and does not reach the detector side. Therefore, each had the disadvantage that it was difficult to obtain an infrared absorption spectrum.

On the other hand, a photoacoustic infrared spectrometer (FTIR/PAS) does not detect the infrared light that has passed through the sample, but rather uses the heat (concentration wave) generated by the modulated infrared light absorbed by the sample. In order to detect sound waves, regardless of the shape of the sample, such as a black sample or a spherical (or particulate) sample, if even a small amount of modulated infrared light is absorbed, light corresponding to the infrared absorption spectrum will be detected. Acoustic spectrum (FT I R
/PA spectrum) can be obtained. However, since the photoacoustic signal itself is inherently quite weak,
The modulated infrared light to be irradiated had to be irradiated onto the entire relatively large amount of sample in the container without being narrowed down. Furthermore, with conventional analyzers, the photoacoustic signals obtained from minute samples were quite weak, even if they were obtained at all, so photoacoustic infrared spectra (FT I R/PA spectra)
When converted into , there was a drawback that the S/N ratio was small. For this reason, it has conventionally been considered unsuitable for measuring micro samples with a size of 100 μm or less, for example.

(Problems to be Solved by the Invention) The present invention solves the problem of measuring from several μl to 1100 μl, which has been difficult to measure in the past.
uφ minute black sample or minute spherical (or particulate)
It is an object of the present invention to provide a signal detection device for photoacoustic infrared analysis that can obtain a photoacoustic infrared spectrum with a sufficiently large S/N ratio even for an analysis sample.

[Structure of the Invention (Means for Solving the Problems)] In order to solve the above problems, the present invention aims to efficiently irradiate only a minute sample with modulated infrared light, thereby reducing the weak photoacoustic sound generated. In order to capture the signal well, we installed a mechanism that prevents photoacoustic signals from other parts of the sample from being mixed in, and in order to amplify weak photoacoustic signals, we introduced an arbitrary gas (filling gas) into the sealed signal detector. The solution was to inject it.

Furthermore, we took measures to change the volume while keeping the pressure inside the container constant to resonate and increase the photoacoustic signal.

That is, the present invention provides a light source for irradiating modulated infrared light onto an analysis sample, a condensing mirror for narrowing down the modulated infrared light, and a modulated infrared light source disposed between the light source and the condensing mirror. It has an aperture for controlling the light irradiation area and a closed space for accommodating the analysis sample, and a crystal plate that transmits modulated infrared light is provided on the modulated infrared light irradiation side of this closed space. A signal detector consisting of a signal detector, a high-sensitivity microphone placed in the closed space of this detector to detect the photoacoustic signal generated by irradiating the analysis sample with modulated infrared light, and a high-sensitivity microphone. A preamplifier for amplifying the detected photoacoustic signal, a data processing device for performing Fourier transform on the photoacoustic signal of the analysis sample to obtain a photoacoustic spectrum corresponding to an infrared absorption spectrum, and processing of this data. The present invention provides a signal detection device for photoacoustic infrared spectroscopy, characterized in that it is equipped with a recorder for recording results.

The signal detector described above includes a means for changing the volume of the closed space around the sample in order to resonate and increase the photoacoustic signal obtained by the high-sensitivity microphone, and a gas introduction device for introducing gas into the closed space. and a discharge path, and a pressure sensor provided in the gas introduction and discharge path to adjust the pressure of any gas so that the pressure in the closed space remains constant when changing the volume of the closed space. It is also possible to have a mechanism.

(Function) In the present invention, modulated infrared light is efficiently irradiated only on minute analysis samples, and the generated weak photoacoustic signals are successfully captured. When measuring a minute black sample or a minute spherical (or particulate) sample, as long as the sample itself absorbs even a small amount of modulated infrared light, a photoacoustic infrared spectrum (FTI) corresponding to the infrared absorption spectrum can be obtained. R/PA
Spectrum) is obtained.

Note that the present invention is effective when the sample made of an organic material to be analyzed is minute or in trace amount, and the base is a material such as metal or ceramics that does not transmit infrared rays.
For example, 1) particle surface treatment agents such as silicon nitride, silicon carbide, and aluminum nitride, 2) organic thin films for various sensors such as polymer-sensitive films on the surface of humidity sensors, and 3) LCD TVs.
It can also be used to analyze the resin film of color filters.

(Example) Hereinafter, the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a schematic diagram showing an embodiment of a signal detection device for photoacoustic infrared spectroscopy according to the present invention.

As shown in the figure, this signal detection device for photoacoustic infrared spectroscopy includes a light source 1 for emitting modulated infrared light 1a that is irradiated onto an analysis sample, and a condenser mirror for narrowing down the modulated infrared light 1a. (for example, a Cassegrain mirror) 3, these light sources 1, and a condensing mirror 3
A diaphragm, that is, an aperture 2, is disposed between the aperture 2 and the aperture 2 to control the irradiation area of the modulated infrared light 1a. A first lens barrel 4 equipped with a half mirror 5 that is removably inserted in the arrow direction between the modulated infrared light 1a, and a second lens barrel 6 equipped with a mirror 7 and a white light source 8. , an analysis sample a provided downstream from the condenser mirror 3
and a crystal plate 1 that transmits modulated infrared light on the modulated infrared light irradiation side of the closed space S.
A signal detector 10 is provided with a signal detector 10 provided with a signal detector 10, and a signal detector 10 is arranged in a closed space S of this detector 10, and a modulated infrared light 1 is provided to a microsample a for analysis.
a high-sensitivity microphone 12 for detecting a photoacoustic signal generated by irradiating a, a preamplifier 13 connected to the high-sensitivity microphone 12 for amplifying the detected photoacoustic signal, and a closed space S. In order to resonate and increase the photoacoustic signal obtained by the high-sensitivity microphone of piston 14) and microsample 1
A data processing device 16 for Fourier transforming the photoacoustic signal of a to obtain a photoacoustic spectrum corresponding to an infrared absorption spectrum, a recorder 17 for recording the data processing results, and a gas introduced into the closed space. A gas introduction path 18 and a discharge path 19 are provided for the gas introduction path 18 and the discharge path 19, and an arbitrary gas is provided in the gas introduction path 18 and the discharge path 19 so that the pressure in the closed space S remains constant when the volume of the closed space S is changed. Valve mechanism 20 with a pressure sensor for adjusting the pressure
．． 21, and the detection device is set at x and y so that the modulated infrared light to be irradiated can be set at any position.

It is equipped with a fine movement adjustment mechanism (not shown) for moving by minute distances in any direction on the Z axis.

Note that the first lens barrel 4 and the second lens barrel 6 can be replaced with other optical means. Further, as the crystal plate 11, potassium bromide (KBr), cesium iodide (Cs
A material transparent to infrared rays such as sample a
In addition to preventing the weak photoacoustic signal generated from leaking to the outside of the detector 10, the gas filled inside the detector,
For example, this is necessary to prevent xenon (Xe) from leaking outside the detector. Therefore rubber backing 22
may be used to further enhance confidentiality.

This gas is filled to increase the weak photoacoustic signal and to exclude water vapor existing in the sealed space S inside the detector and water vapor generated from the sample a. Although the fine movement adjustment mechanism has been described as one that moves the entire detector 10, it is not limited to this, and may also be one that moves only a part of the detector 10, that is, the sample placement part, or one that moves the optical system part. It's okay.

Next, a method of using this signal detection device for photoacoustic infrared spectroscopy will be explained.

First, in order to observe a sample, a first lens barrel 4 equipped with a half mirror 5 and a second lens barrel 6 equipped with a mirror 7 and a white light source 8 are inserted into the optical path, and the white light source 8 emits light. After the visible light is narrowed down by the Cassegrain mirror 3 and the optical path area is controlled by the aperture 2 if necessary, the first lens barrel 4 and the second lens barrel 6 are pulled out from the optical path. Next, for measurement, modulated infrared light 1 modulated by, for example, a Michelson interferometer is made to enter the sample a in the detector 10 through the same optical path as the above-mentioned visible light. At this time, the modulated infrared light 1 focused by the condenser mirror 3 is irradiated onto the sample via the crystal plate 11. As a result, the photoacoustic signal generated from the microsample a is detected by the high-sensitivity microphone 12,
After being amplified by the preamplifier 13, it is sent to the data processing device 16.

At this time, the piston 14 is moved by the step motors 1 and 5 to gradually change the volume of the sealed space inside the detector, so that the position where the photoacoustic signal generated from the sample increases due to the resonance phenomenon is determined. , constant preamplifier 1
3 is fed back to the data processing device 16. The interior of the detector S is filled with gas by opening and closing a valve 20 controlled by the data processing device 16. The pressure inside the detector S is constantly monitored by a pressure sensor built into the valve 20 and sent to the data processing device 16.

By changing the piston 14 and performing Fourier transform on the photoacoustic signal in the data processing device 16 at the position where the photoacoustic signal detected by the high-sensitivity microphone 12 is maximum, a photoacoustic infrared spectrum (FTIR/PAS spectrum) is obtained. is obtained. This result is recorded by the recorder 17.

Next, using the above-mentioned detection device, the particles were treated with a surface treatment agent made of bisphenol A type epoxy resin.
The results of measuring 0μm aluminum nitride particles are shown in the second
As shown in the figure. In addition, Figure 2 shows aluminum nitride powder and
The photoacoustic infrared spectrum containing the surface treatment agent is shown, and the result obtained by subtracting the known infrared absorption spectrum of aluminum nitride from this infrared absorption spectrum is bisphenol A.
It matches well with the infrared absorption spectrum of type epoxy resin. As a result, it is clear that analysis can be performed with high accuracy by using the detection device according to the present invention.

[Effects of the Invention] As explained above, according to the present invention, it is possible to measure a small black sample or a small spherical (or particulate) sample in the range of several μIm to 100 μmφ, which has been difficult to measure in the past. As long as it absorbs even a small amount of modulated infrared light, a photoacoustic infrared spectrum (FT I R/PA spectrum) corresponding to an infrared absorption spectrum can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a signal detection device for photoacoustic infrared spectroscopy according to an embodiment of the present invention, and FIG. 2 is a photoacoustic infrared spectrum obtained by the device of the present invention. DESCRIPTION OF SYMBOLS 1... Modulated infrared light, 2... Aperture, 3... Condenser mirror, 4... First lens barrel, 6... Second lens barrel, 10
...Signal detector for photoacoustic infrared spectroscopy, 11...
Crystal plate, 12... High sensitivity microphone, 13...
Preamplifier, 14... Piston, 15... Step motor, 16... Data processing device, 17... Recorder.

Claims (1)

[Claims] A light source that irradiates the analysis sample with modulated infrared light, a condensing mirror that narrows down the modulated infrared light, and a condensing mirror disposed between the light source and the condensing mirror to control the irradiation area of the modulated infrared light. an aperture and a closed space for accommodating the analysis sample,
Moreover, a signal detector is provided with a crystal plate that transmits modulated infrared light on the modulated infrared light irradiation side of this closed space, and a signal detector is provided in the closed space of this detector, and the modulated infrared light is applied to the analysis sample. A high-sensitivity microphone for detecting the photoacoustic signal generated by irradiation with Signal detection for photoacoustic infrared spectroscopy, comprising: a data processing device for obtaining a photoacoustic spectrum corresponding to an infrared absorption spectrum; and a recorder for recording the data processing results. Device.