JPH035538B2 - - Google Patents

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 coupled to 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, it is generally not possible to record a chromatogram with a spectrophotometer, 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 chromatographic column, and the fluid effluent from this column is led to flow cell F. This conduit is branched in the middle, and a portion of the column outflow fluid is guided to a chromatographic detector D. M surrounded by a chain line is a Michelson interferometer, and L is a light source. In this example, the light emitted from the interferometer M passes through the flow cell F and enters the photodetector P. Chromatographic detector D
The chromatogram is monitored by the chromatogram, and when the peak of the 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, which can later be Fourier transformed to obtain the absorption spectrum of the sample components. Here, the interferogram is recorded a certain period of time after the peak of the chromatogram is detected, depending on the length of the pipe from branch point B to chromatography detector D, and the length from B to flow cell F.
Since the lengths of the pipes up to the point F are not equal in design, the time at which the concentration peak of the sample component reaches F is later than the time at which the concentration peak of the sample component reaches D, so this delay time is expected. varies depending on the carrier flow rate and various other factors, so it is not always possible to record the maximum interferogram of a sample component when the concentration of the sample component in flow cell F is at its maximum. If it is outside the range, sufficient analytical sensitivity will not be obtained. This is one of the problems with conventional devices. This problem is not unique to the use of a Fourier transform spectrophotometer, but also exists when a chromatograph and other types of spectrophotometers are combined. However, this problem can be solved by taking advantage of the Fourier transform spectrophotometer's ability to scan wavelengths at high speed. That is, while the chromatograph is in operation, the interferogram is obtained by repeatedly scanning the wavelength of the interferometer, and then the absorption spectrum is obtained by Fourier transform, and the spectrum is integrated, and the results are recorded. This method involves creating a record corresponding to grams, monitoring it, detecting its peak, and storing the spectrum at that time. However, in this method, calculations such as Fourier transformation of the interferogram and its integration are performed for each wavelength scan, so a very high-speed calculation device is required, resulting in an extremely expensive chromatograph and spectrophotometer. This is the second problem.

The present invention was made with the aim of solving the two problems mentioned above, and is
Applying Parseval's theorem, the basic principle of chromatography-Fourier transform spectroscopy is to obtain values corresponding to sample component concentrations by squaring and integrating the interferogram, and finally record this value. It provides a photometer. The present invention will be explained below with reference to Examples.

FIG. 2 shows an embodiment of the invention. C is a chromatographic column, F is a flow cell, and M is a Michelson interferometer.The difference from the conventional example shown in FIG. 1 is that there is no chromatographic detector D in FIG. The Fourier transform spectrophotometer, which is composed of a flow cell F and a photodetector P, is characterized in that it 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 one forward trip corresponds to one wavelength scan. When the moving distance of the movable mirror m during the forward stroke is x, each time x changes by λ/2 for light of wavelength λ, the output of the photodetector P for that light changes in intensity for one period. 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 output I of the photodetector as a function I(x) of x, we get
I(x) is given by I(x)=∫ ^∞ _-∞ f(σ) cos2πσxdσ (1). f(σ) corresponds to the spectrum of light, and I(x) is the Fourier transform of f(σ). When I(x) is Fourier transformed again, a spectral function f(σ) is obtained.

Now, according to Parseval's theorem, when the Fourier transform of the function h(t) is H(f), ∫ ^∞ _-∞ h ² (t)dt=K∫ ^∞ _-∞ ｜H(f)｜ ² df …(2 ) holds true. Applying this formula to I(x) above, ∫ ^∞ _-∞ I ² (x) dx = ∫ ^∞ _-∞ f ² (σ) dσ ...(3), and the output of the photodetector P is squared and integrated. By doing this, the square integral of the spectrum can be obtained. What is obtained by this calculation is not the spectrum itself or the integral of the spectrum, but
An increase or decrease in the peak of the chromatogram corresponds to a change in the concentration of the sample component, and a change in concentration corresponds to an increase or decrease in the absorption spectrum. Therefore, the above integral corresponds to the concentration of the sample component in a one-to-one manner, and the peak in the chromatogram corresponds to the change in the concentration of the sample component. The timing of the vertex and the maximum of the integral in equation (3) coincide. Therefore, during operation of the chromatograph, the interferometer M
By repeating wavelength scanning, calculating equation (3) for each wavelength scanning, and recording the integral value, a record equivalent to a chromatogram can be obtained.The peak apex is detected and the interferogram at that time is obtained. By storing this in memory, the absorbance spectrum of the sample component at the peak apex can be obtained by performing Fourier transformation later. The calculation of equation (3) is much simpler and takes less time than Fourier transform.
Therefore, no particularly high-speed arithmetic device is required.

In actual analysis, the light transmitted through the flow cell F is assumed to have a transmittance of 100% or an absorbance of 0 when only the carrier fluid is flowing through the air space, so it is assumed that the flow cell F is empty or only the carrier fluid is flowing. Perform wavelength scanning with , measure the interferogram Ib (x) at that time, calculate and store B = ∫ ^∞ _-∞ Ib ² (x) dx, and then introduce the sample into the chromatograph. The wavelength scan is repeated, the interferogram Is(x) is measured each time, and the above equation (3) is calculated using S=∫ ^∞ _-∞ I ² s(x)dx-B (4).

Returning to Figure 2, A is the amplifier and A/D is the A/D.
The converter, Memb, is an area on the memory that stores the absorbance interferogram Ib(x) when the flow cell F is empty or only the carrier fluid flows, and the CPU is a computer that performs the above calculations. , recorder R records the integral value of equation (4). Furthermore, the computer CPU detects the maximum of the integral value of equation (4), and when the maximum is detected, it stores the interferogram Is(x) in the wavelength scan at that time (or the next time) in the memory. The data is stored in another area MemI, and after the separation operation by chromatography is completed, the MemI data is read out and subjected to Fourier transformation, and the absorbance spectrum is recorded by the recorder R. Q is a sampling circuit which sends a sampling pulse 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 integration of equation (4) above is performed from -∞ to ∞, but in reality, it is sufficient to scan a range of about 1 cm around the position of the optical path difference O between the moving mirror m and the fixed mirror and integrate over that range. It is. If the number of sampling points in one scan is N, then FFT (Fast Fourier
When Fourier transform is performed using a mathematical operation called "Transform", the number of required multiplications X is X=N/2log ₂ N times. On the other hand, in the present invention, the sampling point I(x)
The number of times of multiplication is N because we just square and add
Times are fine. If N is 2 to the 11th power, or 2048 times, then X is
This is 11,264 times, which is about 5 times the 2,048 times of the present invention.
Since multiplication takes much more time than addition, the fact that the number of multiplications can be reduced is significantly effective in shortening the 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 the device combining a chromatograph and a spectrophotometer, by combining the high speed of a Fourier transform spectrophotometer with a high-speed computer. This problem is solved by data arithmetic processing that does not require .It is possible to provide an inexpensive and 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, Q... Sampling circuit.

Claims (1)

[Scope of Claims] 1. A chromatograph, a flow cell through which fluid flows out from the column, a Fourier transform spectrophotometer that spectrally specifies the light transmitted through the cell, and 2. The photometric output obtained by the spectrophotometer. A chromatograph-Fourier transform spectrophotometer comprising an arithmetic circuit that multiplies and integrates and a means for recording the output of the arithmetic circuit. 2. A chromatograph and a flow cell that circulates the fluid flowing out from the column, a Fourier transform spectrophotometer that spectrally spectra the light transmitted through the cell, and an operation that squares and integrates the photometric output obtained by the spectrophotometer. A chromatograph-Fourier transform circuit comprising 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. type spectrophotometer.