JPS6296855A - Light-sound measuring method - Google Patents

Abstract

PURPOSE:To enable high-accuracy light-sound measurement, by specifying a distance value between a thin film plate surface and a cell window and limiting a frequency of an incident beam of light to the specified range. CONSTITUTION:A microphone 2 is fixed to a light-sound cell 1 available for containing a long thin layer chromatograph plate and the microphone 2 and a specimen chamber 3 are connected with a wave guide 4. A cell lid 8 is inserted after the thin layer plate or a specimen of the same size is contained into the chamber 3 and it is pressed against the cell 1. And, a distance between a thin layer plate surface and a cell window 5 is made 0.3-0.7mm and the light-sound signals from the microphone 2 are measured by setting the frequencies of the input irradiated beam into the specimen inside the chamber to 30-100Hz, or more preferably, to 40-80Hz.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a photoacoustic measurement method, and particularly to a method for measuring thin layer chromatographs and plates using light emitting diodes (abbreviated as LEDs, hereinafter) as the source. The present invention relates to a photoacoustic measurement method using a photoacoustic d111 determination device.

(Prior art) Thin layer chromatography
omat.

Graphy (hereinafter abbreviated as TLC) is a method that not only allows a mixture to be separated and analyzed by combining an appropriate stationary phase and mobile phase, but also allows each component to be analyzed simultaneously in a short time.

On the other hand, photoacoustic analysis is an analytical method that utilizes the heat or heat generated during the process of a sample absorbing light and sound and being deactivated without radiation. This method can also be applied to opaque, light-scattering solid samples such as thin-layer plates, and examples of its application to samples developed on thin-layer plates have often been seen in the past.

However, these are placed all around the small capacity cell, and after cutting out the target part of the cucomadogram, enter the cell: I'1. It is complicated to create a calibration curve. In contrast, open-end photoacoustic cells have been developed, but they are not as sensitive as closed cells in terms of measurement sensitivity.

The present inventors have developed an optical sweeping type photoacoustic analyzer that can directly quantify the stationary phase 'Fr' from a thin layer plate without removing or cutting it, and a large thin layer plate that can be stored in the device, such as a conventional large thin layer plate such as 26 x 76 m + n. We have developed a large thin layer plate that cannot be seen.

In this method, intermittent light guided by an original fiber is irradiated onto a thin layer of nanoparticles from above a photoacoustic cell, and the light is quantified while sweeping in XY direction. As a result, the samples on the same thin plate were fixed in the same state, making it possible to repeat measurements and easily create a calibration curve.

In addition, in order to increase the photoacoustic intensity, the light source for photoacoustic measurements usually uses a light source with a high intensity. had the disadvantage of being large and expensive. However, by developing an improved type of device that uses a light emitting diode (hereinafter abbreviated as LED) as a light source, the inventors of the present invention were able to make the device compact and portable, and also significantly reduce the price of the device. Ta.

With LEDs, it is easy to obtain intermittent light through power modulation, and it is also easy to change the intermittent frequency. Therefore, when using a conventional mechanical switch to make the light source beam an intermittent light, the generation of mechanical vibrations and noise is avoided. could be reduced to zero, and a remarkable improvement in the accuracy of the photoacoustic signal could be seen.

However, according to the measurement experience in photoacoustic measurements using the large-capacity cell developed by the present inventors, measurement accuracy is still influenced by the characteristic values, which can also be called device characteristics.
In particular, it is strongly desired to find optimal conditions for the distance between the thin layer plate surface and the cell window and the frequency of input irradiation light in order to improve the accuracy of photoacoustic measurements.

(Problems to be Solved by the Invention) The present invention aims to find optimal conditions in order to solve the problem of improving the accuracy of photoacoustic measurement in a new device that improves the above-mentioned conventional technology.

(Means for Solving the Problems and Their Effects) As a means for solving the above problems, the present invention has a photoacoustic cell that can accommodate a thin layer chromatography plate, and input irradiation light to the surface of the plate. In a photoacoustic measuring device that outputs sound generated by a photoacoustic signal as a photoacoustic signal, the distance between the thin layer grating surface and the cell window is set to 0.3 to 0.7 Hz, and the frequency of input irradiation light is set to 30 to 100 Hz, preferably 40 Hz. ~
The photoacoustic measurement method involves measuring within the range of 80H3.

In explaining the method of the present invention, first, the method of the present invention and the photoacoustic device will be explained.

FIG. 1 shows a structural diagram of a photoacoustic cell. 26×76w
Cell l, which can accommodate n large thin-layer grates, is made of aluminum. As microphone 2, an Enctorenoto condenser microphone is used. To prevent noise from outside the cell, the microphone is glued to the cell using epoxy resin adhesive.
and are connected by a sea urchin guide 4 having an inner diameter of about 1 mm and a length of 15 mm. For example, the sample chamber is 27 x 77 x
Assuming 3 mm, the dimensions of the thin layer plate accommodated here are 26 x 76 x 15 mm. A hard glass measuring 93 x 35 x 1.5 m is used as the cell window 5 and is also bonded to the cell 1 with an epoxy resin adhesive. 6 is a cell body, and 7 is a prenonya release. After storing a thin layer plate or a sample of the same size in a cell (1), a cell lid 8 with a one-piece thick rubber pad is inserted and pressed into the cell (1).

Cell volume 1 is approximately 6.9 crn3. The microphone output was amplified using a home-made LF 356 H preamplifier. Its power source is a battery, which is controlled by a regulator. The microphone is used with a bias voltage of 4.5 μ applied.

The light source is Toshiba's Ga-Aj-As-based TLRA l.
50 C was used, but its peak wavelength was 660 nm,
A half-width of 3.1 nm and a light emission output of about 3 Cd can be obtained at I=20 mA (C).

For modulation, I used a self-made volteno monoulator using μA355, which has a duty cycle of 20 to 90.
%, the frequency is variable in the range 12-100 Hz. To prevent the LED beam from spreading, the parts except the LED head were covered with aluminum foil.

This results in a beam diameter of 3 on the thin plate.

Attach this to the sweep device at a speed of 10.
Sweep at 6mm/min. The obtained photoacoustic signal is guided to a self-made lock-in amplifier (Toa Seha Co., Ltd.).
EPR-100A model).

Although the photoacoustic i++1+ constant device described above is an outline of a typical device that uses an LED as a light source, the dimensions of the device trough are not limited to the above.

Now, in photoacoustic spectroscopy, the photoacoustic signal is inversely proportional to the cell volume. When the thin layer plate is housed in the cell, the cell volume is the value obtained by subtracting the volume of the thin layer Punto from the total cell volume. Spacers of different thicknesses (made of aluminum, for example) are inserted under the thin layer plate to finely adjust the cell volume, but the air volume through which acoustic waves propagate inside the cell is smaller than the thin layer plate. The dimensions of the spacer are almost the same as those of the cell except for the thickness, and the side spacing is just enough to allow it to be stored in and taken out from the cell. It can be considered by converting it into the distance to the window.

In this way, the distance from the thin layer plate v-) surface to the cell window can be varied by inserting various covers of different thicknesses as described above, and the intensity of the photoacoustic signal txi-i can be increased. ;
As a result of determining y, a relationship diagram as shown in FIG. 2 was obtained.

As is clear from this figure, the photoacoustic signal intensity is maximum when the distance between the thin layer plate surface and the cell window is about 0.5+mn. If the above distance is less than 0.3 mm, the cell volume decreases, but the generation of the photoacoustic signal that is sent out in a piston-like manner from the heat diffusion surface of the thin layer Punt is hindered, so the signal strength decreases, making it unsuitable for further purposes. do not have. Also, the above distance is 0.
When it exceeds 7 an, the signal strength decreases rapidly and the purpose of the measurement is again not achieved.

From the above, it has been found that the optimal range of the distance between the thin layer Punto surface and the cell window to achieve the present purpose is 0.3 mn to 0.7 mn.

In addition, in the above measurements, the microphone and cell window are fixed to the cell body with epoxy resin as described above, so the removal of external noise is good. is what was obtained.

Now, in photoacoustic spectroscopy, the photoacoustic signal intensity is also inversely proportional to the intermittent frequency of the light source.

In the method of the present invention, as described above, an LED is used as a light source, and the LED has a light emission intensity of about 1.5.
Since the ratio of mW is relatively low, it is conceivable that quantification can be achieved with a better S/N ratio if used at a lower frequency, but this has not yet been determined.

For this reason, the inventors of the present invention earnestly investigated the relationship between the frequency of the input irradiation light and the signal intensity, and as a result, were able to discover the relationship between the two as shown in FIG.

In this figure, the distance between the TLC surface and the cell window is constant 0.7
It was sore throat. The sample contained 05μgN of Amido Plaque IOB.
It is determined by the peak height of the signal intensity recorded on the recorder when a spot is placed on the layer plate and the LED is swept. Also shown in the figure are numerical values determined regarding changes in the S/N ratio.

It is clear from this figure that the maximum value of signal strength is = 15
Hz, and the peak of the S/N ratio is near 60 Hz. At a frequency of 40 Hz, the signal strength is still almost comparable to the peak at 45 Hz, but 3
At frequencies below 0 Hz, the signal strength rapidly decreases because the distance between the TLC surface and the cell window is smaller than the heat diffusion distance of the air. However, surrounding noise increases as the frequency becomes lower, so when looking at the S/N ratio, it is still low at 45 Hz, and the frequency is slightly higher (the S/N ratio peaks around 60 Hz. If complete soundproofing and photographic prevention are possible, the best frequency is 45 Hz in terms of sensitivity.Also, since the detection lower limit is likely to be dominated by the magnitude of surrounding noise, the S/N ratio should be set at 45 Hz. It is clear that the higher the /N ratio, the more sensitive quantitative results can be obtained.
Above z, it is not appropriate.

As a result of finding the relationship between frequency, signal strength, and S/N ratio, if we combine these results, the frequency of input irradiation light is 30
A range of Hz to 100 Hz is preferred, more preferably a range of 40 Hz to 80 Hz has been found to be optimal.

To summarize the above, the distance between the TLC surface and the cell window is 03~
Setting the input source frequency to 30 to 100 Hz enables photoacoustic measurement with high precision, and it is clear that the measurement method is inappropriate if it deviates from the above range.

[Brief explanation of drawings]

Figure 1 is a structural diagram of a photoacoustic 11111 device according to the method of the present invention, Figure 2 is the relationship between the distance between the TLC surface and the cell window and the original acoustic signal intensity, and Figure 3 is the relationship between the frequency of input irradiation light and z. A relationship diagram between acoustic signal strength and S/N ratio is shown. ■-Cell, 2-Microphone, 3-I feed room, 1-Unive guide, 5-Cell window, 6-Cell body, Hooplenoja release, 8-Cell lid.

Claims (1)

[Claims] In a photoacoustic measurement device that has a photoacoustic cell that can accommodate a thin layer chromatography plate and outputs the sound generated by input light to the plate surface as a photoacoustic signal, the distance between the thin layer plate surface and the cell window is 0.3 to 0.7
mm, and the frequency of the input irradiation light is 30 to 100 Hz.
A photoacoustic measurement method characterized by measuring within the range of.