JPH03226632A - Signal processor for spectrophotometer - Google Patents

Abstract

PURPOSE:To improve wavelength resolutions and measuring sensitivity by determining a device function using a bright line of a light source and correcting the sample spectrum according to the function. CONSTITUTION:A column effluent flows to a flow cell 36 to perform a detection with a photodiode array 42. When a sample value(in)(n is sample point number) of a true light intensity spectrum is given, a spectrum(i'n)observed is expressed by a relationship of convolution between the spectrum(in) and an impulse response(hn) as apparatus function. To determine the impulse response(hn), a discharge tube is used as light source 32. A bright line spectrum proper to an atom sealed in the light source 32 without setting a sample with a spectrophotometer set on conditions the same as those when the sample is measured. An observation data for a peak of the bright line is given as impulse response(hn) of a smoothing filter. A inverted filter(gn) is determined from the impulse response(hn). Then, a true sample spectrum(in) is calculated utilizing an inverted filter (gn)determined using the bright line of the light source 32 for the observation spectrum(i'n) of the sample with the flowing of the sample.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a signal processing device that processes signals obtained from a spectrophotometer used in a liquid chromatograph detector or the like.

(Prior Art) Spectrophotometers are used in a variety of fields including, for example, detectors for liquid chromatographs. After being absorbed by a sample and passed through a slit, the light is separated using a diffraction grating, and the luminous intensity of each wavelength is converted into an electrical signal using a photoelectric conversion element such as a photodiode.

In a spectrophotometer, narrowing the slit width improves wavelength resolution, but the amount of light decreases, resulting in a decrease in sensitivity.
The noise level increases.

Conversely, increasing the slit width improves sensitivity, but the image obtained by the spectrometer becomes wider and the wavelength resolution decreases.

(Problems to be Solved by the Invention) When a multi-channel detector such as a photodiode array is used as a detector for a spectrophotometer.

Light of a single wavelength spreads on the detector surface due to the influence of the slit width, etc., and the wavelength resolution decreases.

Accordingly, one object of the present invention is to provide a signal processing device that can improve the wavelength resolution by correcting the blurring of a spectral image, and can increase the sensitivity by widening the slit width.

(Means for solving problems) The invention is illustrated in FIG.

2 is a light source, 4 is a sample, and 6 is an optical system of a spectrophotometer.

8 is a detector such as a photodiode array, and 10 is an A/D converter that converts the detection signal of the detector 8 into a digital signal. Reference numeral 12 denotes an instrument function storage unit that stores the digital value of the observed spectrum when the emission line of the light source is measured under the same conditions as the sample measurement without installing a sample, and 14 stores the digital value of the observed spectrum obtained by measuring the sample. The observed spectrum storage unit 16 is an arithmetic unit that corrects waveform distortion of the observed spectrum of the sample in the observed spectrum storage unit 14 based on the device function in the device function storage unit 12.

In a preferred embodiment of the calculation unit 16, as shown in FIG. (Function) A phenomenon in which a spectral image is blurred due to the influence of the slit width of the optical system of a spectrophotometer, etc. If we consider that this is the effect of a linear smoothing filter with the wavelength axis as the time axis, we can identify this linear filter and find its inverse filter.If we pass the observed blurred spectrum through this inverse filter, we can obtain the original value. A high-resolution spectrum is recovered.

By finding an inverse filter and correcting the blurring of the spectral image caused by the optical system, the wavelength resolution can be improved.2 Also, by improving the wavelength resolution, it is possible to prevent a decrease in resolution even when using a wide slit. , sensitivity can be improved.

(Example) FIG. 3 shows an example of an optical system in one embodiment.

32 is a light source, and 34 is a concave mirror that allows the light from the light source 32 to enter the diffraction grating 40 through the slit 38. A flow cell 36 is provided between the concave mirror 34 and the slit 38 to which the liquid chromatograph column effluent is guided. 42 is a photodiode array that receives the light separated by the diffraction grating 40. An A/44 converts the detection signal of the photodiode array 42 into a digital signal.
It is a D converter.

The sample value of the true luminous intensity spectrum is 1(n) (n is the sample point number and is considered to be the element number of the photodiode array 42). ), then the observed spectrum 1(n) is.

It is expressed by the convolution relationship between the true luminous intensity spectrum 1(n) and the impulse response h(n), which is an instrument function, such as 1(n)=i(n)ning h(n). This means that the observed spectrum 1
(n) can be considered as the true luminous intensity spectrum 1(n) passed through a linear smoothing filter with an impulse response h(n).

Therefore, a filter with the opposite effect of equation (1), that is, 1(n)-i(n) Book g(n) When you seek evening light, you pass it through this filter.

A true spectrum 1(n) with high wavelength resolution can be obtained from a blurred observed spectrum 1(n).

This is a wavelength domain method.

In order to obtain the impulse response h(n), which is a device function, as shown in FIG. 4, a discharge tube such as a deuterium lamp is used as a light source, and an emission line spectrum specific to the enclosed atoms is utilized. Measure the bright line spectrum of the light source without installing a sample using a spectrophotometer set to the same conditions as those used for sample measurement.

Since the bright line of the light source is considered to be an impulse input to the smoothing filter, the observation data for the peak of the bright line becomes the impulse response h (n ) of the smoothing filter. From its impulse response h(n), the inverse filter g(n)
seek.

Next, as shown in FIG. 5, the sample is poured and measured. Using an inverse filter g(n) obtained using the emission line of the light source for the observed spectrum i(n) of the sample, (
2) Perform calculations using formulas.

Calculate the true sample spectrum 1(n).

FIGS. 6 and 7 show a signal processing method using a frequency domain method realized by the arithmetic unit shown in FIG.

When formula (1) is converted into 2, we get △ I(z) = I(z) ・H(z) however, I(z)=ZT Ha I (z) = ZT H(z)=ZT and ZT[] [1(n)] △ [1(n) [h(n)] represents two transformations.

(3) therefore.

I(z)=I(z)/H(z) --(4).

In Uni, since the number of sample points is finite, Z transformation can be realized by complex Fourier transformation.

As shown in FIG. 6, the spectrometer is set to the same conditions as those for sample measurement, and the emission line spectrum of the light source is measured without setting up the sample. The obtained impulse response h(n) is subjected to complex Fourier transform to obtain H(z).

Next, as shown in Fig. 7, sample measurement is performed, and the observed spectrum 1(n) obtained is complex Fourier transformed to I(z).
get.

Next, the Fourier transform I(z) of the sample spectrum is divided by the Fourier transform H(z) of the impulse response. When the inverse Fourier transform of the division result is obtained, this becomes the corrected sample spectrum 1(n).

The above example assumes that the degree of blur does not depend on the wavelength. However, if the degree of blur differs depending on the wavelength, the impulse response h( n) should be corrected.

In addition, other filtering operations for the purpose of noise removal, for example, can be performed simultaneously using the five frequency domain method.

(Effects of the Invention) In the present invention, an instrument function is determined using the emission line of the light source, and the sample spectrum is corrected using the instrument function, so that the wavelength resolution is improved.

Furthermore, even if a wide slit is used, it is possible to prevent the resolution from deteriorating, making it possible to widen the slit width and perform high-sensitivity measurements.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the present invention, FIG. 2 is a block diagram showing a calculation section in a preferred embodiment of the invention, and FIG. 3 is a configuration diagram showing an optical system of one embodiment. 4 and 5 are flowcharts showing a wavelength domain method as one embodiment, and FIGS. 6 and 7 are flowcharts showing a frequency domain method as another embodiment. 2...Light source, 4...Sample, 6...
...Optical system, 8...Detector, 10...
A/D converter, 12... Device function storage section, 14
...Observation spectrum storage section, 16...
Arithmetic unit, 18... Complex Fourier transform unit, 20.
...Complex division section, 22...Complex inverse Fourier transform section.

Claims (2)

[Claims] (1) An instrument function memory section that stores the digital value of the observed spectrum when the emission line of the light source is measured under the same conditions as the sample measurement without placing the sample on the spectrophotometer, and A signal of a spectrophotometer comprising an observed spectrum storage unit that stores digital values of the observed spectrum obtained, and an arithmetic unit that corrects waveform distortion of the observed spectrum of the sample based on the device function in the device function storage unit. Processing equipment. (2) The calculation unit includes a Fourier transform unit that performs Fourier transform on the instrument function and the observed spectrum of the sample, a division unit that divides the Fourier transform of the observed spectrum of the sample by the Fourier transform of the instrument function, and an inverse Fourier transform of the division value. 2. The signal processing device for a spectrophotometer according to claim 1, further comprising an inverse Fourier transform section that performs the following.