JPH0460441A - Photoacoustic cell for absorption analysis measurement of liquid sample - Google Patents

Abstract

PURPOSE:To enable execution of acoustic-wave measurement being sensitive sufficiently to a modulated light for measurement modulated at a specific wavelength and sensitive to a sound pressure, by providing an acoustic-wave measuring piezoelectric body stuck on a cylindrical resonator into which a measuring tube is fitly inserted. CONSTITUTION:When a modulation signal is oscillated from a modulation signal generator 42, a laser diode driver 43 drives a laser diode 45 and a laser light is emitted from the diode 45. The laser light is applied to the position of the antinode of an acoustic wave in a photoacoustic cell 30 wherein a sample liquid 20 is stored. In this case, the sample liquid 20 generates a heat with absorption of the light, a periodic heat current is brought forth and thereby the sample liquid 20 is made to vibrate. With the vibration of the sample liquid 20, a resonator 38 resonates and a piezoelectric member 40 converts this vibration into an electric signal. Moreover, the electric signal is amplified by a preamplifier 47 and subjected to a prescribed signal processing 48 through a lock-in amplifier 44. This constitution enables execution of acoustic-wave measurement being sensitive sufficiently to a modulated light for measurement modulated at frequencies of several tens of KHz to several MHz and sensitive to sound pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Fields] The present invention is a method for measuring liquid sample absorption, which measures sound waves generated by the generation of heat accompanying light absorption of a liquid sample by irradiating the liquid sample with modulated light for measurement. This invention relates to a photoacoustic cell for analysis and measurement.

[Conventional technology] Conventionally, liquid samples such as liquids and semi-fluids are irradiated with modulated light for measurement, and the samples are analyzed by measuring the sound waves generated by the generation of heat accompanying light absorption in the liquid samples. Sample absorption analysis measurement devices are known.

As shown in FIG. 3, the photoacoustic cell 10 for optical analysis and measurement that measures the sound waves has quartz glass plates 13 and 14 attached to both ends of a cylindrical tube 12.

O-rings 18 and 19 are fitted between the quartz glass plate 13 and the cylindrical tube 12 and between the quartz glass plate 14 and the cylindrical tube 12 to maintain airtightness.
These constitute an airtight sample box 22 in which the sample liquid 20 is stored.

Further, an L-shaped vibrator 24 is connected to a hole bored in the upper part of the cylindrical tube 12, and a microphone 26 that is mainly sensitive to frequencies below 10 kHz is arranged at the tip of the vibrator 24. ing.

Further, as the modulated light for measurement, for example, amplitude-modulated laser light is used, and a mechanical chopper or the like that can be used at a frequency of 1 kHz or less is used for modulation.

Next, the operation will be explained.

A sample liquid 20 is sealed in a sample box 22, and when modulated light (for example, laser light) is irradiated onto the sample liquid 20 from outside the sample box 22 through the quartz glass plate 13, the sample liquid 20 absorbs the laser light.

At this time, the sample liquid 20 generates heat as it absorbs light, and a periodic heat flow due to this heat generates a sound wave.

Then, by collecting and measuring this sound wave with the microphone 26, the amount of light absorption of the sample liquid 20 is measured, and qualitative and quantitative analysis of the sample liquid 20 is performed based on this amount of light absorption.

[Problems to be Solved by the Invention] As mentioned above, the conventional liquid sample absorption analysis measuring device has the following problems:
A mechanical chopper or the like that can be used at a frequency of 1 kHz or less is used to modulate the modulated light for measurement, and a microphone sensitive to particle displacement is used to receive a photoacoustic signal as a signal proportional to particle displacement.

In this case, the sensitivity decreases in inverse proportion to the modulation frequency, so there is a restriction that it must be used at at most 1kHz or less, so it easily picks up ambient noise, is susceptible to vibration, and requires time for signal processing. There were some problems. In addition, since signal processing takes time, it is easy to cause a decrease in reproducibility due to changes in physical properties due to constant temperature rise of the sample liquid and signal drift due to thermal motion, and a decrease in reliability due to temperature drift in the amplifier circuit. In addition, there was a problem that commercial frequency noise could not be effectively removed because it was too close to the commercial frequency.

Furthermore, since the vapor and droplets of the sample liquid reach the bonded parts of the microphone and cell, they have poor durability and are easily soiled, resulting in a lack of reliability when measuring trace amounts.

Purpose of the Invention The present invention has been made in view of the above-mentioned conventional problems.
The purpose is to provide a photoacoustic cell for liquid sample absorption analysis measurement that has sufficient sensitivity to measurement modulated light modulated at several tens of kHz to several MHz and is sensitive to sound pressure.

[Means for Solving the Problems] In order to achieve the above object, the photoacoustic cell for liquid sample absorption analysis measurement according to the present invention irradiates a liquid sample with modulated light for measurement, and absorbs the light absorption heat of the liquid sample. A liquid sample absorption analysis measuring device for analyzing the liquid sample by measuring sound waves generated by the liquid sample, comprising: a transparent measurement tube into which the liquid sample is placed; a sound wave reflecting gate valve provided at both ends of the measurement tube; It is characterized by comprising a cylindrical resonator into which a measurement tube is inserted, and a piezoelectric material for measuring sound waves attached to the resonator.

[Operation] According to the above configuration, the liquid sample to be analyzed is sealed between the sound wave reflecting gate valves in the measurement tube. Then, the sound waves generated when the liquid sample is irradiated with the modulated light for measurement are transmitted through a resonator into which a measurement tube is inserted, and detected by the sound wave measurement piezoelectric body.

[Example〕 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a preferred embodiment of a photoacoustic cell 30 for use in a liquid sample absorption analysis n1 determination apparatus.

As shown in the figure, this photoacoustic cell 30 has a quartz tube 32 as a transparent long and narrow resonant tube, and a manual cock with a large acoustic impedance is installed at both ends of the quartz tube 32 to separate a liquid sample. Valves 34,36 are arranged. Here, a sample chamber 22 in which a sample liquid 20 is stored is formed by a quartz tube 32 between both gate valves 34 and 36.

A cylindrical resonator 38 made of a metal member such as aluminum or brass is fitted onto the quartz tube 32. A ring-shaped piezoelectric member 40 made of PZT or the like is adhered to the outer peripheral surface of the resonator 38, thereby forming a resensor.

Although not shown, a laser beam as modulated light for measurement is irradiated from the side of the quartz tube 32, and the sample liquid 20 stored in the sample chamber 22 is irradiated with the laser beam. As a result, the sample liquid 20 generates heat as it absorbs light, thereby generating sound waves.

Further, if the length between the gate valves is L1 and the sound velocity is V, then if the generated sound wave has a predetermined frequency of vibration, the frequency f and the wavelength λ can be determined by the following equation.

f-Vn/2L [Hz co・(100
)λ−21−/n−=(101
)(n-2, 3, 4...) For example, if the generated sound wave is the third harmonic vibration, the sound pressure distribution will be as shown in FIG. Here, the resonator 38 is fitted onto the outside so as to be at the antinode position, and the laser beam is similarly irradiated to the antinode position where the resonator 38 is not located.

Next, the configuration of a liquid sample absorption analysis measurement apparatus using the photoacoustic cell 30 described above will be explained using FIG.

In the figure, 42 is a modulation signal generator for modulating the modulated light for measurement, and the output of this modulation signal generator 42 is sent to a laser diode driver 43 and also to a lock-in amplifier 44, which will be described later. It is sent as a synchronization signal.

A laser diode 45 is also connected to the laser diode driver 43, and the laser light emitted from the laser diode 45 is irradiated onto the photoacoustic cell 30 by an optical system 46 such as a lens.

Furthermore, a preamplifier 47 is connected to the output side of the piezoelectric member 40 of the photoacoustic cell 30 for liquid sample absorption analysis measurement, and the lock-in amplifier 44 is connected to the preamplifier 47.

A signal processor 48 is connected to the lock-in amplifier 44, and a display 49 and a recorder 50 are connected to the signal processor 48.

Here, when the modulation signal from the modulation signal generator 42 is oscillated, the laser diode driver 43 drives the laser diode 45 using the oscillated modulation signal, and the laser diode 45 emits a laser beam.

Then, the laser light is irradiated onto the antinode of the sound wave in the liquid sample absorption analysis measurement photoacoustic cell 30 in which the sample liquid 20 is stored in the sample chamber 22 .

In this case, the sample liquid 20 stored in the sample chamber 22 generates heat as it absorbs light, and this heat generates a periodic heat flow, causing the sample liquid 20 to vibrate. Note that the frequency f and wavelength λ of this sound wave are obtained from the above equations (100) and (101).

Then, the resonator 38 resonates with the vibration of the sample liquid 20,
Ring-shaped PZT adhered to the outer peripheral surface of the resonator 38
The piezoelectric member 40 converts this vibration into an electrical signal.

Further, the electrical signal converted by the piezoelectric member 40 is amplified by a preamplifier 47, and the amplified signal is input to a signal processor 48 via a lock-in amplifier 44, where predetermined signal processing is performed.

Thereafter, the processing results of the signal processor 48 (qualitative/quantitative analysis results of the sample liquid 20) are displayed on the display 49 and recorded on the recorder 50.

Here, in the experiment conducted by the applicant, the photoacoustic cell 3
0 has been confirmed to have sufficient sensitivity to laser light modulated at several tens of kHz to several MHz.

In the above embodiment, manual cocks were used for the gate valves 34 and 36, but the present invention is not limited to this, and electromagnetic valves or the like may be used. In this way, the photoacoustic cell 30 can be placed inside the piping of a factory production line and used for online monitoring.

In addition, a piezoelectric member 40 is used to adjust the resonance Q value of the sensor.
It is also possible to attach a rubber material to the outer periphery of the sensor or mold the sensor.

Furthermore, in the above embodiment, explanation was given using a laser diode, but if the frequency f is limited to several MHz or more,
Xe lamps or other lasers can be used.

[Effects of the Invention] As explained above, according to the photoacoustic cell for liquid sample absorption analysis measurement according to the present invention, a sensor having sufficient sensitivity to modulated light modulated at several tens of kHz to several MHz can be used. Since this has been realized, it is possible to perform measurements while separating noise such as surrounding power supply noise, and it is also possible to provide a photoacoustic cell that is extremely resistant to vibrations. Furthermore, the detection signal is less susceptible to drift due to a rise in the temperature of the sample to be measured, making it possible to improve reproducibility in measurement. In addition, since the sample is encapsulated, the vapor and powder of the sample will not scatter to the sensor or other parts that perform the measurement, making it possible to extremely safely and improve the reliability of the measurement.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the configuration of a photoacoustic cell for liquid sample absorption analysis measurement of the present invention, FIG. 2 is a block diagram showing the configuration of an experimental apparatus incorporating the photoacoustic cell for liquid sample absorption analysis measurement of the present invention, FIG. 3 is a sectional view showing the configuration of a conventional photoacoustic cell for absorption analysis measurement of a liquid sample. 30... Photoacoustic cell 32 for liquid sample absorption analysis measurement
... Quartz tube 34, 36 ... Gate valve 38 ... Resonator 40 ... Piezoelectric member

Claims (1)

[Scope of Claims] A liquid sample absorption analysis measurement device that analyzes the liquid sample by irradiating the liquid sample with a modulated light for measurement and measuring sound waves generated by light absorption heat of the liquid sample, comprising: a transparent measurement tube into which the measurement tube is inserted, a sound wave reflecting gate valve provided at both ends of the measurement tube, a cylindrical resonator into which the measurement tube is fitted, and a sound wave measurement piezoelectric body affixed to the resonator. A photoacoustic cell for liquid sample absorption analysis measurement, characterized in that it has the following.