JPS6145765B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a dual beam spectrophotometer.

A two-beam spectrophotometer is more effective than a single-beam spectrophotometer in that it can eliminate wavelength dependence of the emission intensity of the light source, the diffraction efficiency of the spectrometer, the sensitivity of the detector, etc. Generally, as shown in FIG. 1, light from a light source 20 is separated into a sample beam 1 and a reference beam 2, which are a sample cell 10 and a reference cell 10', respectively.
is irradiated. Usually, the reference cell 10 contains a solvent,
The sample cell 10 contains a solvent and a measurement sample.
The light transmitted through each cell is detected by the spectral detection section 30
After being separated into spectra, it is converted into an electrical signal. The optical system from the light source to the detector uses a rotating sector to separate and combine the light beams, a beam splitter, a spectrometer placed between the light source and the cell, and two detectors. A variety of configurations are known. The electrical signal from the spectral detection section 30 is used in a divider 40 to calculate the ratio between the amount of light transmitted through the reference cell 10' and the amount of light transmitted through the sample cell 10.
In addition to the divider, optical methods such as the dynode feedback method, the slit servo method, and the optical zero method are also known as means for obtaining the ratio between the reference light and the sample light. After the ratio is determined by the divider 40,
It is logarithmically converted by a logarithmic converter 50 and recorded on a recorder 60 as absorbance.

Although various wavelength dependencies can be removed by using a dual-beam spectrophotometer with the above configuration, there is a problem in that accurate sample spectra cannot be obtained. This point will be further explained using FIG. 2. In FIG. 2a, values obtained by separately logarithmically converting the transmission of the sample cell 10 and the reference cell 10' out of the output of the spectrometer detector 30 in FIG. 1 are expressed as A _S and _AR . In principle, at a wave number position where there is no absorption by the measurement sample, A
_S and A _R match. Figure 2b shows the value after subtracting A _R from A _S and corresponds to the output of the logarithmic converter 50 in Figure 1, but due to the discrepancy between A _S and A _R , the solvent-specific interference absorption I is Appears. This interference absorption I
In particular, when only a trace amount of the sample to be measured is obtained or the concentration is low, this superimposes on the spectrum of the sample to be measured, making it impossible to obtain an accurate sample spectrum and, therefore, making quantitative analysis impossible.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a two-beam spectrophotometer that can obtain accurate sample spectra without interference absorption inherent in solvents.

In the present invention, a correction coefficient is determined so that a sample spectrum and a reference spectrum match each other at a wavelength position where there is no absorption by the sample, and then the reference spectrum is corrected and the sample spectra are compared.

In explaining one embodiment of the present invention, the reason why interference absorption inherent to the solvent occurs will be explained. The absorbances A _S and A _R are determined by the optical path length of the sample cell being _S , the optical path length of the reference cell being _R , the molecular extinction coefficients of the solvent and sample at a specific wavenumber being α ₁ and α ₂ , and the concentration of the solvent and sample in the sample cell being α 1 and α 2 . If C _1S , C _2S , and the solvent and sample concentrations in the reference cell are C _1R and C _2R , it is given by the following equation.

A _S =α ₁・C _1S・_S +α ₂・C _2S・_S (1) A _R =α ₁・C _1R・_R +α ₂・C _2R・_R (2) Here, if the reference cell contains the sample If not, equation (2) becomes A _R ′=α ₁・C _1R・_R (3) The output A after logarithmic transformation is the difference between A _S and A _R ′, and is expressed as the following equation: Become.

A=α ₂・C _2S・_S + α ₁ (C _1S・_S −C _1R・_R (4) In other words, in order to prevent interference absorption by the solvent, the second term on the right side of equation (4) must be zero. For this purpose, it is necessary that the optical path lengths of the sample cell and the reference cell be equal, and that the solvent concentrations in each cell be equal.

An embodiment of the present invention will be described below.
In the present invention, there is no particular requirement that the optical path lengths of the cells be equal or that the solvent concentrations be equal. FIG. 3 is a basic block diagram of one embodiment of the present invention. The same reference numerals as in FIG. 1 indicate the same parts. 70 is an analog-to-digital converter that converts the output signal of the spectroscopic detector 30 into a digital signal. 80 is an arithmetic storage device that takes in the digital signal 7 and performs storage and calculation based on the wave number scanning signal 9 synchronized with the wave number scanning of the spectroscopic detector 30. 90 is a display/recording device that displays and records the output signal 8 of the arithmetic/storage device 80.

Next, the operation will be explained. First, a cell 10 containing only a solvent is installed in the sample beam 1, and nothing is installed in the reference beam 2. Spectral detector 30
When wavelength scanning is performed, signals corresponding to the transmittance display of A _R in FIG. 2a are sequentially outputted from the spectroscopic detector 30. The signal is then converted into a digital signal by the analog-to-digital converter 70 and taken into the arithmetic storage device 80. Arithmetic storage device 8
0, the captured signals are logarithmically converted and sequentially stored at predetermined addresses based on the wavelength scanning signal 9. Next, a cell 10 containing a solvent and a sample is installed in the sample light beam 1. The signal obtained by wavelength scanning of the spectroscopic detector 30 is stored at a predetermined address in the arithmetic storage device 80 in the same manner as described above. In the arithmetic storage device 80, the second term of equation (4),
That is, calculation is performed so that (C _1S・_S −C _1R・_R ) becomes zero, and the result is displayed on the display/recording device 9.
Displayed and stored as 0.

Here, a specific example of the arithmetic storage device 80 will be explained using FIG. 4. Analog-to-digital converter 7 when only solvent is contained in the cell 10
The output signal 7 of 0 is passed through a logarithmic converter 81 and sent as an absorbance signal to a storage device 8 via a changeover switch 82.
5 is stored. The stored address is sequentially incremented by a wave number scanning signal 9 synchronized with the wave number scanning of the spectroscopic detector 30. Next, cell 1 containing the solvent and sample
0 is placed in the sample light beam, and after switching the changeover switch 82, the sample spectrum is measured. The logarithmically transformed sample spectrum is input to one input terminal of the subtracter 87. Further, the reference spectrum stored in the storage device 85 is read out by the wavelength scanning signal 9, and is input to the other input terminal of the subtracter 87 via the multiplier 83 in synchronization with the sample spectrum. Here, α ₂・C _2S・ in equation (4)
Let _S be A′ _S (ν), and α ₁・C _1S・_S be A′ _R
(ν) and α ₁・C _1R・_R is A _R (ν), then the coefficient k placed in the coefficient digitizer 84 is
It satisfies the following formula.

A′ _R (ν)−k・A _R (ν)=0 Therefore, the output of the multiplier 83 is k・A _R (ν)
Therefore, the sample spectrum is A _S (ν) + A′ _R (ν)
becomes. The output of the subtracter 87 is as follows.

A′ _S (ν) + A′ _R (ν) − k・A _R (ν) (6) Here, since the condition of equation (5) is satisfied, A=A′ _S (ν), and the true A sample spectrum is obtained. This result is sent to the output converter 89 on the display/recording device 9.
This results in a signal with a shape suitable for 0.

Next, a method of assigning the coefficient k to the coefficient assigner 84 will be explained. First, a wave number ν ₀ at which it is considered that there is no absorption by the sample is selected. Then, a reference spectrum is obtained, and the wave number of the spectrometer is set to ν ₀ with the sample and solvent placed in the sample beam. Therefore, the storage device 85 outputs a signal A _R (ν ₀ ), and the signal after logarithmic transformation of the output signal 7 is
A′ _R (ν ₀ ). When the switch 91 is turned on at this point, a negative feedback circuit from the corrector 88 to the coefficient digitizer 84 is formed, and the corrector 88 is connected to the subtracter 8.
The contents of the coefficient digitizer 84 are changed so that the output of 7 becomes zero. After setting the number in this way, the switch 91 is opened and measurement of the sample spectrum is started. Figure 6 represents each spectrum, Figure 6a represents the reference spectrum A _R , Figure 6b
represents the sample spectrum A _S . here,
Respective values A _R (ν ₀ ) and A _S at wave number ν ₀
When the coefficient k is determined so that (v ₀ ) is equal, the spectrum shown in FIG. 6d is obtained on the display/recording device 90. In this spectrum, errors due to differences in the optical path length of the cells and differences in solvent concentration are corrected, and a true sample spectrum is obtained.

In the above explanation, the storage device is assumed to be one series, and the sample spectrum is directly input to the subtracter 87. Both spectra may be read out and corrected in synchronization.

Further, the spectrum to be measured and stored first may be a sample spectrum instead of the reference spectrum. In any case, memorize one spectrum,
It may be corrected by comparing with the other spectrum.

Further, the reference spectrum and the sample spectrum may be measured using the same cell. That is, after measuring only the solvent, it is also possible to add a sample to the same cell and measure the sample spectrum. In this case, there is no difference in the optical path length of the cells, but the solvent is diluted by the sample, and there is a difference in the concentration of the solvent, which can be corrected.

In addition, if the wave number ν ₀ for determining the coefficient k cannot be determined in advance, please refer to Figure 6 a and b.
Alternatively, the appropriate wave number ν ₀ may be determined after recording the spectra of each.

In addition, in the above explanation, the coefficient k is determined and corrected after obtaining the absorbance display spectrum.
It is also possible to perform correction based on the spectrum of the transmittance display, which is an antilogarithmically transformed form of the absorbance display. However, in this case, the correction becomes somewhat complicated.

Furthermore, the configuration shown in FIG. 4 can be realized using analog circuits, digital circuits, etc.
Further, it is also possible to implement it using a digital computer or the like.

According to one embodiment of the present invention, an accurate sample spectrum can be obtained by eliminating the effects of differences in optical path length and solvent concentration.

Another embodiment of the present invention will be described with reference to FIG. The same reference numerals as in FIG. 4 indicate the same parts. The feature of this embodiment lies in the method of assigning coefficients, which is particularly effective when the wave number at which no absorption occurs by the sample is unknown. After storing the reference spectrum in the storage device 85, a cell containing the sample and solvent is placed in the sample beam. Switch the switch 82 to the input side of the divider 86, and switch the switch 92 to the input side of the divider 86.
is switched to the output side of the divider 86. As the spectrometer scans the wavelength, a logarithmically converted sample spectrum signal is input to one input terminal of the divider 86, and the other input terminal receives the reference signal in the storage device 85 in synchronization with the wavelength scan. Spectrum input. Divider 86
The ratio of both spectra is determined at and recorded via an output converter 89. The spectrum is as shown in FIG. 6c. Here, at a wavenumber where there is no absorption by the sample, the absorbance ratio is approximately 1. Therefore, it is sufficient to select a wave number ν ₀ at which the absorbance ratio is approximately close to 1. If the switch 91 is turned on after setting the spectrometer at the wave number ν ₀ , the ratio of both spectra at the wave number ν ₀ is set in the coefficient digitizer 84. Then, by switching the changeover switch 92 to the output side of the subtracter 87 and performing normal wavelength scanning, an accurate sample spectrum can be obtained in the same manner as in FIG.

According to another embodiment of the present invention, an accurate sample spectrum can be obtained by eliminating the effects of differences in optical path length and solvent concentration.

Furthermore, it is possible to easily select a wave number at which no absorption occurs by the sample.

According to the present invention, it is possible to obtain an accurate sample spectrum without interference absorption inherent in the solvent.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional two-beam spectrophotometer, FIG. 2 is an explanatory diagram of interference absorption by a solvent, and FIGS. 3 to 5 are block diagrams of embodiments of the present invention. FIG. 6 is an explanatory diagram of correction of interference absorption. 10... Cell, 20... Light source, 30... Spectroscopic detector,
80... Arithmetic storage device, 83... Multiplier, 84... Coefficient digitizer, 85... Storage device, 87... Subtractor, 90...
Display recording device.

Claims (1)

[Claims] 1 In a two-beam spectrophotometer that displays and records the spectrum obtained by comparing the optical signals obtained from the first and second beams, it is obtained when a cell containing a solvent is installed in one of the two beams. A means for storing a reference spectrum and a cell containing a solvent and a sample in one of the two beams are installed, and among the sample spectra obtained, the values of the sample spectrum and the reference spectrum at a wavelength position where there is no absorption by the sample are determined. Two-beam spectroscopy characterized by comprising means for obtaining coefficients that match, means for correcting the reference spectrum based on the coefficients, and means for comparing the corrected reference spectrum and the sample spectrum. Photometer.