JP2649667B2 - Multi-component analysis method in spectroscopic analysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention irradiates a sample with light from a light source, and analyzes the concentration of multiple components contained in the sample based on an absorption spectrum obtained at that time. The present invention relates to a multicomponent analysis method in spectroscopic analysis.

[Conventional technology]

Conventionally, in the multi-component analysis method in the spectroscopic analysis, the absolute value of the absorbance (a value based on the absorbance 0, for example, based on Lambert-Beer's law that the absorbance is proportional to the concentration of the component to be measured, for example, P ₁ shown in FIG.
To _pn ) by a linear algebraic method to analyze the concentration of multi-components. However, this method has the drawback that if a nonlinear disturbance such as noise or drift occurs, the calculated solution becomes extremely unstable, and the calculation of the solution is performed by matrix calculation. And there is a lack of swiftness.

Therefore, as a method of solving such a drawback of the conventional technique, for example, as shown in JP-A-2-55938, the absolute value of the absorbance is selectively multiplied by several constants to obtain a multi-component. It has been proposed to perform a concentration analysis.

[Problems to be solved by the invention]

However, the method disclosed in the above publication has the following disadvantages. In other words, the absolute value of the absorbance must be selectively multiplied by several constants, and a matrix calculation must be performed for an extremely simple superposition such as two components to be measured. In addition to the disadvantage that the processing is extremely complicated, the method also selectively multiplies the absolute value of the absorbance, so that it is susceptible to the potential noise and the base of the absorption spectrum. If the line drifts due to environmental factors such as temperature and humidity, there is a drawback that errors are likely to occur, such as multiplication of non-true values.

The present invention is, local peak value in the peak P ₁ (Yamachi) p ₁ and valley values in the valley V ₁ corresponding to the peak P ₁ (valley value) in the absorption spectrum shown in the Figure 7 v ₁
(Relative absorbance LA ₁ ), and when such local peaks are determined at a plurality of points P _{1 to} P _n , that is, a plurality of local peaks P ₁ to P ₁ of the component to be measured in FIG. Even if P _n is superimposed on the slow absorption of other components that are not the target component (the absorption spectrum of the target component is affected by the absorption spectrum of the other component that is not the target component). ), At a plurality of points not affected by other components, the peak values p ₁ to P _n of the local peaks P _{1 to} P _n
The p _n and relative absorbance LA ₁ ~LA _n of the measurement target component by taking the difference between the valley value v ₁ to v _n of the local valley V ₁ ~V _n corresponding respectively to the local peaks P ₁ to P _n as well as arranged to compute, in which the sum of their relative absorbance LA ₁ ~LA _n is made by utilizing the property such proportional to the concentration of the measurement target component, it is an object of the of the sample An object of the present invention is to provide a multi-component analysis method for spectroscopic analysis that can obtain each of the component concentrations much more easily and quickly than in the past, and that is not easily affected by disturbance or noise.

[Means for solving the problem]

In order to achieve the above-mentioned object, a multi-component analysis method in spectroscopic analysis according to the present invention irradiates a sample with light from a light source, and based on an absorption spectrum obtained at that time, a concentration of the multi-component contained in the sample. In the method of analyzing a plurality of points that are not subject to interference of other components that are not the measurement target component are defined in the absorption spectrum of the measurement target component, and the peak values of the local peaks P _{1 to} P _n at these points and the local calculates the sum of the relative absorbance is the difference between the valley value of the local valley V ₁ ~V _n corresponding respectively to peaks P ₁ to P _n, and the sum of the relative absorbance is proportional to the concentration of the component It is characterized in that the concentration of each of the components is obtained separately by using the sum of the relative absorbances and calculating the proportions separately.

[Action]

For example, when the local peak of the component gas to be measured is superimposed on the smooth absorption of another gas that is not the component to be measured, or the absorption output from the spectrometer due to temporal and environmental influences If the spectrum is totally displaced from the original (eg, the baseline of the absorption spectrum is drifting), as a result, the absolute value of the peak is different from the original absorbance of the peak, but the A plurality of points not subject to interference of other components that are not the target component are determined in the absorption spectrum of the measurement target component, and the peak values of the local peaks at these points and the valley values of the local valleys corresponding to the local peaks, respectively. Since the sum of the relative absorbance, which is the difference from the above, was obtained, the above-described relative absorbance is hardly affected by such influence.
When a local peak of another gas interferes, a value obtained by subtracting the contribution of the interference gas gives the relative absorbance of only the component to be measured.

In other words, since the points of the absorption spectrum are determined for each component that will be contained in the sample, the sum of the relative absorbances can be calculated using points that do not receive interference from other components that are not the measurement target components. In addition, since there are multiple points, interference and noise of other components contained in the absorption spectrum of exhaust gas can be averaged, and even if many components are contained in the sample, it is hardly affected by disturbance and noise. Highly accurate spectroscopic analysis can be performed. Further, conventionally, even for an extremely simple superposition of two components to be measured, the calculation process is extremely complicated and the processing speed is slow, for example, it is necessary to perform a matrix calculation. Not only when the measurement target component is two components, but also when the sample contains three or more multicomponents,
Each of the concentrations of each component can be quickly obtained using a proportional calculation which is much simpler than the matrix calculation.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

First, FIG. 1 schematically shows an example of an apparatus for performing a multi-component analysis method in spectroscopic analysis according to the present invention. In this figure, reference numeral 1 denotes an FT-IR (Fourier transform infrared analyzer). , An analysis unit 2 and a data processing unit 3 for processing an interferogram output from the analysis unit 2.

The analysis unit 2 includes a light source 4 configured to emit a parallel infrared beam, a beam splitter 5, a fixed mirror 6,
An interference mechanism 8 composed of a movable mirror 7; a cell 9 for accommodating a measurement sample and the like and irradiated with an infrared beam from the light source 4 via the interference mechanism 8; and a detector 10 composed of a semiconductor detector and the like
It is composed of

The data processing unit 3 includes, for example, an averaging processing unit 11 for averaging the interferograms,
A fast Fourier transform processing unit 12 that performs a fast Fourier transform on the output data from 1; a spectrum calculation unit 13 that performs a spectrum calculation on the component to be measured based on the output data from the fast Fourier transform processing unit 12; I have.

Although not shown, the FT-IR1 is provided with a drive mechanism for driving the movable mirror 5 of the interference mechanism 8 in, for example, the X-Y direction. A controller for controlling each of the three processing units 11 to 13 is provided.

Thus, according to the FT-IR1 configured as described above, the cell 9 accommodates the comparative sample or the measurement sample, respectively, and irradiates the cell 9 with the infrared beam from the light source 4 to obtain the comparison sample and the measurement sample. Measure the interferogram. And
After obtaining a power spectrum by Fourier transforming each of these interferograms, the ratio of the power spectrum of the measurement sample to the power spectrum of the background is obtained, and by converting this to an absorbance scale, an absorption spectrum can be obtained. it can.

Next, details of the method of the present invention will be described based on an example in which exhaust gas (hereinafter simply referred to as “exhaust gas”) of a methanol-fueled vehicle is determined for methanol (gas) and formaldehyde (gas).

FIG. 2 shows a reference absorption spectrum obtained by FT-IR1 shown in FIG. 1, where A is 103.7p
Reference absorption spectrum with methanol only at pm, B is 2
Reference absorption spectrum with only 6.4 ppm formaldehyde, and C shows absorption spectrum of exhaust gas. In this figure, the vertical axis indicating the absorbance uses an arbitrary scale.

From this figure, the absorption spectrum C of the exhaust gas is a superposition of the reference absorption spectrum A of methanol and the reference absorption spectrum B of formaldehyde, and there is no absorption by gases other than these two gas components in this wave number range. I understand.

Figure 3 is a wave number 2790cm ^-1 ~ wavenumber 2730cm ^-1 in Figure 2
In this range, a moderate absorption of methanol and a plurality of local peaks of formaldehyde are observed.

Then, in the reference absorption spectrum B of formaldehyde, a plurality of points not affected by methanol are determined, and the peak values of the local peaks at these points and the valley values of the local valleys corresponding to the local peaks are determined. Find the sum of the relative absorbances, which is the difference.
That is, five points are defined within the range of wave numbers 2790 cm ^-1 to 2730 cm ^-1 , and a local peak at each point and five local valleys corresponding to the local peaks, that is, five pairs of Peak, valley ((P _B1 , V _B1 ) to (P
_B5, singled out V _B5)), P _B1 ~P peak value of _B5 and P _B1 to P _B5
The sum of the relative absorbances (Total Span) obtained by calculation based on the valley values of V _{B1 to} V _B5 respectively corresponding to the above is 1.3998.

Further, five pairs of peaks and valleys in the reference absorption spectrum B of formaldehyde ((P _B1 , V _B1 ) to (P _B5 ,
V _B5 )) is calculated based on the peak value and the valley value of the five pairs of peaks and valleys ((P _C1 , V _C1 ) to (P _C5 , V _C5 )) in the absorption spectrum C of the exhaust gas corresponding to V _B5 )). The sum of the obtained relative absorbances is 0.7499.

On the other hand, since the concentration of formaldehyde in the reference absorption spectrum B of formaldehyde is 26.4 ppm, when proportionally calculated using the sum of this figure and the relative absorbance,
The concentration of formaldehyde in the absorption spectrum C of the exhaust gas is 14.14 (= 26. × 0.7499 / 1.3998) ppm.

Next, FIG. 4 shows the wave number 2870 cm ⁻¹ to the wave number 28 in FIG.
This is an enlarged view of the range of 10 cm ⁻¹ , in which a plurality of local peaks of methanol and a relatively small peak of formaldehyde are observed.

Then, in the same manner as described above, a plurality of points not affected by formaldehyde are defined in the absorption spectrum A of methanol, and the difference between the peak value of the local peak and the valley value of the local valley at these points. Find the sum of the relative absorbances. That is, wave number 2870cm
Five points are defined within a range of ^-1 to a wave number of 2810 cm ^-1 , and a local peak and a local valley at each point, that is, five pairs of peaks and valleys ((P _A1 , V _A1 ) to (P _A5 ,
V _A5 )) is selected and the sum of the relative absorbances is calculated to be 0.4241. Further, five pairs of peaks and valleys in the reference absorption spectrum A of methanol ((P _A1 , V _A1 )
To (P _A5 , V _A5 )), five pairs of peaks, valleys ((P _B1 ,
The sum of the relative absorbances of (V _B1 ) to (P _B5 , V _B5 )) and the five pairs of peaks and valleys ((P _C1 , V _C1 ) to (P _C5 , V _C5 )) in the absorption and absorption spectrum C of the exhaust gas The sum of the absorbances is -0.01559 and 0.2841, respectively.

The sum of the relative absorbances of only methanol corrected by performing a proportional calculation based on the formaldehyde concentration calculated above is 0.2924, and the concentration of methanol in the reference absorption spectrum A of methanol is 103.7 ppm. When the proportional calculation is performed using the sum of the above and the relative absorbance, the concentration of methanol in the absorption spectrum C of the exhaust gas is estimated to be 71.50 (= 103.7 × 0.2924 / 0.4241).

As described above, when determining the amount of methanol in the exhaust gas, the concentration of methanol can be quantified by correcting the formaldehyde interference even if it is affected.
At this time, it goes without saying that the formaldehyde concentration can be determined together. These results show good agreement with the results of analysis by other gas analysis methods, indicating that the method of the present invention is useful.

Further, FIGS. 5 and 6 show the same treatment as that for formaldehyde and methanol, respectively, performed on the reference absorption spectrum of another gas to show the selectivity of the method of the present invention for the gas species. From FIG. 6, it can be seen that according to the method of the present invention, the selectivity of gas species is high. The concentrations of the reference absorption spectra used to create the above figures are as shown in the following table, and the unit of the concentration is ppm.

The present invention is not limited only to the above-described embodiment. For example, as a means for obtaining an absorption spectrum, an apparatus other than the configuration shown in FIG. 1 may be used. May be. The sample to be analyzed is not limited to gas, but may be liquid or solid.

Further, according to the present invention, even when three or more multi-components are contained in a sample, each component can be analyzed with high accuracy similarly to the above-described embodiment.

〔The invention's effect〕

The present invention provides a method for irradiating a sample with light from a light source and analyzing the concentration of multi-components contained in the sample based on an absorption spectrum obtained at that time. the point does not receive advance determined plurality in the absorption spectrum of the measurement target component, a local valley V ₁ ~ respectively corresponding to the local peaks P ₁ to P _n the local peaks P ₁ to P _n peak values of at these points V _n
The sum of the relative absorbance, which is the difference from the valley value, and
The fact that the sum of the relative absorbances is proportional to the concentration of the component and the proportional calculation using the sum of the relative absorbances are used to separately obtain the concentrations of the components have the following effects.

The noise contained in the absorption spectrum can be averaged by including the absorbances at multiple points in the absorption spectrum (a plurality of points in the absorption spectrum) in the calculation.

When observing the absorption spectrum continuously for a relatively long time, even if distortion (drift) occurs in the absorption spectrum for some reason, it is hardly affected by the distortion.

Even if interference due to smooth absorption is caused by components other than the measurement target, there is no need to correct this.

It is a very simple and high-speed method in practical use, and is easy to implement as a program on a computer.

That is, in the present invention, even if a sample contains many components, highly accurate spectroscopic analysis that is not easily affected by disturbance or noise can be performed. This defines the points of the absorption spectrum for each component that will be included in the sample,
For example, even when the plurality of local peaks P _{B1 to} P _B5 of formaldehyde in FIG. 3 are superimposed on the slow absorption of methanol, that is, when the measurement target is formaldehyde, the absorption spectrum of the formaldehyde is , Peaks of local peaks P _{B1 to} P _{B5 at} a plurality of points that are not affected by the other component (methanol) even if they are affected by the absorption spectrum of another component that is not the measurement target component such as methanol. Value and local peak P
By calculating the sum of the relative absorbances of formaldehyde by taking the differences from the valley values of the local valleys V _{B1 to} V _B5 respectively corresponding to _{B1 to} P _B5 , the interference of other components contained in the absorption spectrum of the exhaust gas is calculated. And noise can be averaged. Also, conventionally, even for an extremely simple superposition such that the number of components to be measured is two, the calculation processing is extremely complicated and the processing speed is slow, for example, it is necessary to perform a matrix calculation. Not only when the number of components to be measured is two, but also when three or more components are contained in a sample, the respective concentrations of each component are calculated by a proportional calculation which is much easier than the matrix calculation. It is possible to quickly and accurately obtain the concentration of each component by using it.

[Brief description of the drawings]

FIG. 1 schematically shows an example of an apparatus for carrying out the method of the present invention, FIG. 2 shows a reference absorption spectrum used in the method of the present invention, and FIG. 3 shows a part of FIG. FIG. 4 is an enlarged view, FIG. 4 is an enlarged view of another part of FIG. 2, FIG.
FIG. 6 and FIG. 6 are diagrams each showing the selectivity of the method of the present invention with respect to gas species. FIG. 7 is a view showing a general absorption spectrum for explaining a problem of the prior art. P _{A1 to} P _A5 , P _{B1 to} P _B5 , P _{C1 to} P _C5 ... local peak, V _{A1 to} V
_{A5, V B1 ~V B5, V} C1 ~V C5 ...... locally Valley.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-304140 (JP, A) JP-A-1-235834 (JP, A) JP-A-60-122357 (JP, A)

Claims (1)

(57) [Claims] In a method for irradiating a sample with light from a light source and analyzing the concentration of multicomponents contained in the sample based on an absorption spectrum obtained at that time, interference of other components which are not components to be measured is provided. It is determined in advance more in the absorption spectrum of the measurement target component a point that does not undergo a local valley V ₁ respectively corresponding to the local peak P ₁ to P _n the local peaks P ₁ to P _n peak values of at these points ~ V _n
The sum of the relative absorbance, which is the difference from the valley value, and
A spectroscopic analysis utilizing the fact that the sum of the relative absorbances is proportional to the concentration of the component, and performing a proportional calculation using the sum of the relative absorbances to obtain the concentrations of the respective components separately. Multi-component analysis method.