JPH04361154A - Method and device for performing optoacoustic spectral analysis - Google Patents

Abstract

PURPOSE:To enable a small of sample to be analyzed by compensating for a change in optoacoustic signal accompanied by a change in a liquid property value of a liquid to be measured. CONSTITUTION:When a value which shows one or more liquid property of a constant-pressure specific heat, an isothermic inflation coefficient, and a sound speed is changed, its liquid property value is directly measured by a liquid property monitor 1 or is obtained by measuring a concentration or a liquid temperature of a coexisting substance. On the other hand, an optoacoustic signal of a sample constituent which is an object to be measured is measured by an optoacoustic analyzer 2, the measurement values are sent to en operation- processing device 3, and a change in the optoacoustic signal according to a change in the liquid property value is compensated by using the changed liquid property value, thus obtaining the concentration of the sample.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method and apparatus for analyzing the concentration of a trace sample in a liquid, and in particular to a photoacoustic spectrometer suitable for analyzing the concentration of a trace sample in a liquid whose liquid properties change. Related to analytical methods and devices.

0002

[Prior Art] Conventional methods and apparatus for photoacoustic spectroscopic analysis of sample concentration in liquids are described in Analytical Chemistry, Vol. 58, No. 11, September, 1986, 2275-
2278 pages (Analytical Chemist
ry, Vol. 58, Sept. 1986, pp227
As described in 5-2278), a technique for making photoacoustic spectroscopy highly sensitive has been studied, but there is no description of the case where the value of the liquid property of the liquid to be measured changes. Generally, in photoacoustic spectroscopy, a sample is sealed in a cell and irradiated with monochromatic light whose intensity is modulated at an appropriate frequency. Absorption by the sample results in periodic thermal expansion of the sample, which propagates as a sound wave. This method detects this with a highly sensitive acoustic detector placed in contact with the cell and analyzes the sample concentration.

0003

[Problems to be Solved by the Invention] In the conventional method and apparatus for photoacoustic spectroscopic analysis of the concentration of components in a liquid, techniques for increasing the sensitivity of photoacoustic spectroscopy have been studied;
No consideration has been given to correcting changes in the photoacoustic signal due to changes in the liquid property values of the liquid to be measured, making it difficult to perform photoacoustic spectroscopic analysis of sample concentration in systems where the liquid property values change. There was a problem.

[0004] An object of the present invention is to provide a photoacoustic spectroscopy method and apparatus that corrects changes in photoacoustic signals caused by changes in liquid properties of a liquid to be measured and analyzes minute sample concentrations. It is in.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the photoacoustic spectroscopy method according to the present invention includes a method for measuring a sample concentration in a liquid using a photoacoustic signal. The structure is such that at least one of the liquid property values of constant pressure specific heat, isothermal expansion coefficient, and sonic velocity of the liquid that changes is measured, and the photoacoustic signal is corrected using each liquid property value.

[0006] When a liquid contains coexisting substances and the value of each liquid property changes depending on the concentration of the coexisting substance, the photoacoustic signal measures the concentration and calculates the value of each liquid property corresponding to the concentration. This is a configuration that is corrected using

[0007] Furthermore, when the properties of each liquid change depending on the temperature of the liquid, the photoacoustic signal may be configured such that the temperature is measured and the value of each liquid property measured at the temperature is corrected.

Furthermore, in a photoacoustic spectrometer that measures the concentration of a sample in a liquid using a photoacoustic signal, the liquid property values of the constant pressure specific heat, isothermal expansion coefficient, and sound velocity of the sample liquid are measured. A liquid property monitor that measures at least one of them, a photoacoustic analyzer that measures a photoacoustic signal, input the respective liquid property values and the photoacoustic signal, and use the changed liquid property values to perform optical analysis. The configuration includes an arithmetic processing device that corrects the acoustic signal.

The liquid property monitor is configured to measure the concentration of coexisting substances.

[0010] The liquid property monitor may also be configured to be a monitor that measures the temperature of the liquid.

[0011]

[Operation] According to the photoacoustic spectroscopy method and apparatus of the present invention, the liquid to be measured is sealed in a cell and sent to the liquid property monitor, and the constant pressure specific heat, isothermal expansion coefficient, and sound velocity necessary for correcting the photoacoustic signal are measured. At least one of the liquid property values is measured, and the measured value is sent to an arithmetic processing unit. On the other hand, the photoacoustic signal is measured by a photoacoustic analyzer and sent to a processing unit. The arithmetic processing device corrects the photoacoustic signal using the measured value of the changed liquid properties and calculates the sample concentration as described below. The photoacoustic signal intensity <P> (N/m2) generated in the liquid is expressed as <P>=k(βV2/Cp)EεC, where the excitation light output is E(W).
(1) It is expressed by the formula (1). Here, k is a constant and β is the isothermal expansion coefficient (1/K
), Cp is the specific heat at constant pressure (J/(Kg・K)), and V is the speed of sound (
m/s), ε is the molar extinction coefficient of the sample (m2/mol),
C is the sample concentration (mol/L). In equation (1), the photoacoustic signal intensity is proportional to the sample concentration, indicating that the component concentration can be measured by photoacoustic spectroscopy. Therefore, when k is determined by creating a calibration curve, the sample concentration is determined using the following equation (2).

C=<P>/{k(βV2/Cp)Eε}
(2) However,
By changing β, V, and Cp, which represent the values of liquid properties, the photoacoustic signal changes, which affects the measured value of sample concentration. Further, these values indicating liquid properties change depending on the concentration of coexisting substances in the liquid and the temperature of the liquid. For example, Cp depends on the concentration of coexisting substances, and β depends on the liquid temperature. Therefore, the photoacoustic signal changes due to changes in the concentration of coexisting substances in the liquid and the liquid temperature. Therefore, either directly measure these values, or measure the concentration of coexisting substances and the liquid temperature to find values that indicate the liquid properties.
) and correcting the photoacoustic signal intensity, accurate component concentrations can be determined.

[0013]

[Embodiment] An embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 1, the liquid to be measured is placed in the cell 5.
The liquid is sealed and first sent to the liquid property monitor 1. This liquid property monitor 1 directly measures one or more of the liquid property values of constant pressure specific heat Cp, isothermal expansion coefficient β, and sound velocity V necessary for correcting the photoacoustic signal, or The concentration of coexisting substances and liquid temperature are measured to determine the When measuring the concentration of coexisting substances, it is possible to quickly measure it in-line using measurement methods such as spectrophotometry and fluorescence analysis, and liquid temperature can also be measured in-line using thermocouples, etc. . The value measured by the liquid property monitor 1 is sent to the arithmetic processing unit 3 as a liquid property signal.

On the other hand, a photoacoustic signal representing the concentration of the sample to be measured, which is input to the arithmetic processing unit 3, is measured by the photoacoustic analyzer 2. An example of the device configuration of this photoacoustic analyzer 2 is shown in FIG. In FIG. 2, a pulsed YAG laser 4 is used as a light source, and a dye laser for wavelength modulation and a Raman shifter are combined in order to match the wavelength of the laser beam to the absorption wavelength of the measurement sample. A cell 5 containing a liquid is irradiated with light from this pulsed YAG laser 4, and a signal measured by an acoustic detector installed in the cell 5 is amplified by a preamplifier 6, and a signal is amplified by a boxcar integrator 8. To detect. The excitation light monitor 7
It is used to correct the output fluctuation of the light. The photoacoustic signal obtained as described above is sent to the arithmetic processing device 3 shown in FIG. 1, and the measured values are substituted into the above equation (2) to determine the sample concentration.

An example of measurement according to this embodiment will now be explained. In this measurement, a photoacoustic signal of pentavalent Np ions in a nitric acid solution was measured. The measurement wavelength is 617.0 nm, which is the absorption peak of pentavalent Np ions (Np ions).
and U ions were added as a coexisting substance. Since there is almost no absorption of U ions at this measurement wavelength, the amount of light absorbed does not increase even if U ions coexist, and no photoacoustic signal based on U ions is generated. FIG. 3 shows the concentration dependence of the photoacoustic signal of Np ions when U ions coexist and when they do not. It can be seen from FIG. 3 that the photoacoustic signal intensity increases when U ions coexist. This is because, as shown in FIG. 4, the constant pressure specific heat decreases as the U ion concentration increases, so the photoacoustic signal intensity increases according to equation (1). Therefore, as a liquid property monitor, the U ion concentration was measured by spectrophotometry or fluorescence analysis, and from the results, constant pressure specific heat was determined using FIG. 4, and the photoacoustic signal was corrected. The results are shown in FIG. This figure 5 shows that Np
These are the results of measuring the dependence of the obtained photoacoustic signal on the U ion concentration while keeping the ion concentration constant. From Figure 5, it can be seen that when the change in constant pressure specific heat is not corrected, the photoacoustic signal intensity increases as the number of U ions increases, whereas when it is corrected, the photoacoustic signal intensity is almost constant; is found to be effective. FIG. 6 shows the dependence of the specific heat at constant pressure on the nitric acid concentration, and from this FIG. 6 it can be seen that when the nitric acid concentration changes, it is necessary to monitor the nitric acid concentration as a liquid property monitor.

As described above, according to this embodiment, the sample concentration can be determined by correcting the change in the photoacoustic signal due to the change in the liquid property value using the changed liquid property value. It has characteristics.

[0018]

[Effect of the invention] According to the photoacoustic spectroscopy method of the present invention,
This has the effect of correcting changes in the photoacoustic signal due to changes in the liquid properties of the liquid to be measured, and allowing analysis of minute amounts of samples.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of the photoacoustic analyzer of FIG. 1.

FIG. 3 is a graph showing the concentration dependence of the photoacoustic signal intensity of Np ions.

FIG. 4 is a graph showing the dependence of specific heat at constant pressure on U ion concentration.

FIG. 5 is a graph showing the dependence of photoacoustic signal intensity on U ion concentration when Np ions are constant.

FIG. 6 is a graph showing the dependence of specific heat at constant pressure on nitric acid concentration.

[Explanation of symbols]

1 Liquid property monitor 2 Photoacoustic analyzer 3 Arithmetic processing unit 4 Pulsed YAG laser 5 Cell 6 Preamplifier 7 Excitation light monitor 8 Boxcar integrator

Claims (6)

[Claims] 1. A photoacoustic spectroscopy method for measuring sample concentration in a liquid using a photoacoustic signal, in which at least one of the liquid property values of constant pressure specific heat, isothermal expansion coefficient, and sonic velocity of the liquid that changes the photoacoustic signal is used. A method for photoacoustic spectroscopy, characterized in that the photoacoustic signal is corrected using the values of the respective liquid properties. 2. When there is a coexisting substance in a liquid and the value of each liquid property changes depending on the concentration of the coexisting substance, the photoacoustic signal is used to measure the concentration and to measure each liquid property corresponding to the concentration. 2. The photoacoustic spectroscopy method according to claim 1, wherein the correction is performed using the value of . 3. The photoacoustic signal is characterized in that when each liquid property changes depending on the temperature of the liquid, the temperature is measured and the photoacoustic signal is corrected using the value of each liquid property measured at the temperature. The photoacoustic spectroscopy method according to claim 1. 4. In a photoacoustic spectrometer that measures the concentration of a sample in a liquid using a photoacoustic signal, a liquid that measures at least one of the liquid property values of constant pressure specific heat, isothermal expansion coefficient, and sonic velocity of the sample liquid. A property monitor, a photoacoustic analyzer that measures the photoacoustic signal, inputting the values of each liquid property and the photoacoustic signal, and correcting the photoacoustic signal using the changed values of each liquid property. A photoacoustic spectrometer characterized by comprising a calculation processing unit. 5. The photoacoustic spectrometer according to claim 4, wherein the liquid property monitor is a monitor that measures the concentration of coexisting substances. 6. The photoacoustic spectrometer according to claim 4, wherein the liquid property monitor is a monitor that measures the temperature of the liquid.