JPS593242A - Chromatograph fourier transform type spectrophotometer - Google Patents

Abstract

PURPOSE:To obtain an inexpensive high performance chromatograph-spectrophotometer by squaring and integrating photometry output from a Fourier transform type spectrophotometer to obtain a value for the concentration of sample components, which is memorized sequentially. CONSTITUTION:Interferograms Ib(x) and Is(x) are obtained beforehand with a Fourier transform type sepctrophotometer composed of a Michelson interferometer M, a flow cell F and a photodetector P by way of an amplifier A, an A/D converter A/D and a computer CPU when a carrier fluid alone is flowed through the flow cell F and when a sample is flowed, and both results are memorized into memories Memb and MemI. After squaring the data, they are integrated over the scan section of 1cm regarding the movement distance (x) of a mobile mirror (m) and a difference is determined in the results and recorded sequentially. Thus, a recording is obtained corresponding to a chromatrogram. This operation can be done simply and quickly rather than the Fourier transform without requiring a high speed arithmetic unit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a chromatograph-Fourier transform spectrophotometer that combines a gas chromatograph or a liquid chromatograph with a Fourier transform infrared spectrophotometer or the like.

Fourier transform spectrophotometers can complete one wavelength scan in a short time, so they are suitable for analyzing samples that change in flow, and when combined with a chromatograph, they can immediately perform spectroscopic analysis of sample components separated by the chromatograph. Can be done. Although the chromatography-Fourier transform type spectrophotometer has these characteristics, in general, a spectrophotometer cannot record a chromatogram, so conventional devices of this type have the following drawbacks.

FIG. 1 shows an example of a conventional chromatograph-Fourier transform spectrophotometer. C is a chromatograph, M is a Michelson interferometer, and L is a light source.

In this example, the emitted light from the interferometer M passes through the flow cell F and enters the photodetector P.

Two chromatograph detectors are used to monitor the chromatograph, and when a peak of a sample component is detected, the interferometer performs wavelength scanning at an appropriate fixed time interval and the output of the photodetector P is recorded. This record is an interferogram,
If this is later subjected to Fourier transformation, the absorption spectrum of the sample component can be obtained. In this case, the interferogram is recorded a certain period of time after the peak of chroma I/gram is detected because of the pipe length from branch point B to chromatographic detector D-i and the pipe length from B to flow cell F4. Since the path lengths are unequal in design, the time when the concentration peak of the sample component reaches F is longer than the time when it reaches D, so this lag time is taken into consideration, but this lag time is determined by the carrier flow rate. If you try various things like that, you will not be able to obtain sufficient analytical sensitivity.

This is one of the problems with conventional devices. This problem is a unique problem when using a Fourier transform spectrophotometer.
, rather than combining chromatography and other types of spectrophotometry 1
It exists even if...

By the way, this point can be solved by making use of the characteristic of the Fourier transform spectrophotometer that it can scan wavelengths at high speed. That is, while the chromatograph is in operation, the interferometer repeatedly scans the wavelength to obtain an interferogram, which is then Fourier transformed to obtain an absorption spectrum, which is then integrated, and the results recorded. This method involves creating and monitoring records corresponding to grams, detecting the peaks, and storing the spectrum at that time. However, in this method, calculations such as Fourier transform of the interferogram and its integration are performed for each wide wavelength scan, so a very high-speed calculation device is required17, resulting in an extremely expensive romatograph-spectrophotometer method. This is the second problem.

The present invention was made with the aim of solving two consecutive problems:
] A chromatography-Fourier transform type whose basic principle is to square the interferogram and integrate it to obtain a value corresponding to the sample component concentration, and then record this. A spectrophotometer is provided. The present invention will be explained below with reference to Examples.

FIG. 2 shows an embodiment of the invention. C is the chromatographic column, F is the flow cell, M is the Michelson interference side,
The difference from the conventional example shown in FIG. 1 is that there is no chromatographic detector in FIG. The feature is that the meter also functions as a chromatographic detector. In FIG. 2, L is a light source, m is a movable mirror, which is driven back and forth in the direction of the arrow, and -times of forward travel corresponds to one wavelength scan. If the moving distance of the movable mirror m during the forward stroke is X, then the wavelength λ
Each time X changes by λ/2 for the light, the output of the photodetector P for that light changes in intensity for one cycle. When light has a spectral distribution, the output of the photodetector P changes by one period for each wavelength of light for each half-wavelength movement of the movable mirror, so λ/2 can be written as σ. If we record the photodetector output ■ as a function 1(X) of X, we get ■(
X) is given by. f(σ) corresponds to the spectrum of light, and ■(X) is the Fourier transform of f(σ).

When I (x) is Fourier transformed again, the spectral function f
(σ) is obtained.

Now, according to the Parsθval theorem, when H is the Fourier transform of the function h(t), the following holds true. When this formula is applied to the equation (x), the output of the photodetector P is squared and integrated to obtain the integral of the square of the spectrum. What is obtained by this calculation is not the spectrum itself or the integration of the spectrum, but the increase or decrease in the peak of the chromatogram corresponds to the change in the concentration of the sample component, and the change in concentration corresponds to the increase or decrease in the absorption spectrum. The above integral corresponds to the concentration of the sample component, and the timing of the peak apex of the chromatodarum and the thickest of the integrals in equation (3) coincide. Therefore, during the operation of the chromatograph, the wavelength scanning of the interferometer M is repeated, and the calculation of equation (3) is performed for each wavelength scanning.
By recording the integral value, a record corresponding to the chromatogram can be obtained, and if the peak apex is detected and the interferogram of that ibis is stored in memory, the sample at the peak apex can be obtained by Fourier transformation later. Absorbance spectra of the components can be obtained. The calculation of equation (3) is much simpler and takes less time than Fourier transform, and therefore does not require a particularly high-speed calculation device.

In actual analysis, the transmittance of the light transmitted through the flow cell when the flow cell F is empty or only a carrier fluid is flowing],
Since O0% or absorbance is O, wavelength scanning is performed in advance with flow cell F empty or with only carrier fluid flowing, and at that time, a sample is introduced into the chromatograph and wavelength scanning is repeated. The above formula (3) is calculated using the σ-times interferogram 5(X) using the III constant.

Returning to Figure 2, Mθmb is the amplifier, Maki Mibusi ← Isolation-II piece A/D is the A/D converter, and Mθmb is the absorbance when the above-mentioned flow cell F is empty or only the carrier fluid flows. From the interferogram (x) is an area of 10 memory in which all data are stored, C10 (computer performs the above calculation, and recorder R records the integral value of equation (4). C1) IJ performs ultra-thick detection of the integral value using the (seating) method, and when the maximum is detected, the interferogram IsH in the wavelength scan at that time (or the next time is fine) is stored in another area on the memory. After the chromatographic separation operation is completed, the MemI data is read out and Fourier transformed, and the absorbance spectrum is transferred to the recorder R.
Recorded by. Q is a sampling circuit which sends sampling pulses to the A/D converter A/D every time the movable mirror m moves by a certain amount during the wavelength scanning period by the interferometer M.

The above equation (4) is integrated from 1 to 004, but in reality, 2 is 1 centered at the position of the optical path difference O between the movable mirror m and the fixed mirror.
．． l? It is sufficient to scan a range of 771 positions and integrate within that range. If the number of sampling points in one scan is N, FFT (Fast Fourier r
When Fourier transform is performed using the mathematical operation T r a, n s f Or m ), the number of required multiplications X is
=, co-og2N times. On the other hand, in the present invention, the sampling point (X) is 2
Since all you have to do is multiply and add, the number of additions only needs to be 19. If N is 2 to the ]] power, that is, 2048 times, then X is ]]-2
This is 64 times, which is about 5 times the 2048 times of the present invention. Calculation takes much more time than addition, so
The fact that the number of additions can be reduced is extremely effective in shortening calculation time.

The present invention solves the problem of difficulty in obtaining spectroscopic analysis data at the apex of a chromatogram peak, which is a weak point of a device that combines a chromatograph and a spectrophotometer with a connected structure, by combining the high speed of a Fourier transform spectrophotometer with the high speed This problem is solved by data arithmetic processing that does not require a computer, and it is possible to provide an inexpensive, high-performance chromatograph-spectrophotometer.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional example, and FIG. 2 is a block diagram of an embodiment of the present invention. C...Column, F...Flow cell, P...Photodetector, M...Michelson interferometer, CPU...Computer, R...Recorder, -1Q,...Sampling circuit . Agent Patent Attorney Kosuke Agata

Claims (2)

[Claims] (1) A chromatograph, a flow cell that circulates the fluid flowing out from its column, a Fourier transform spectrophotometer that spectrally spectra the light that passes through the cell, and a calculation that squares and integrates the photometric output obtained by the spectrophotometer. A chromatograph consisting of a circuit and a means for recording the output of the same arithmetic circuit.
Fourier transform spectrophotometer. (2) A chromatograph, a flow cell that circulates the fluid flowing out from the column, a Fourier transform spectrophotometer that spectrally spectra the light that passes through the cell, and a calculation that squares and integrates the photometric output obtained by the spectrophotometer. A chromatograph IJ comprising a circuit, a means for detecting the peak of the output of the arithmetic circuit, and a memory for storing the photometric output for one scan of the Fourier transform spectrophotometer when the peak is detected. Conversion type spectrophotometer.