JP3780634B2 - Chromatographic signal processor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a chromatographic signal processing apparatus. The chromatographic signal processing apparatus of the present invention can be used for all chromatographic apparatuses that separate and detect each component in a sample in time, such as a gas chromatograph apparatus and a liquid chromatograph apparatus.
[0002]
[Prior art]
FIG. 5 is a diagram showing a general configuration of a gas chromatograph apparatus. A carrier gas channel 12, a purge channel 14 and a split channel 16 are connected to the sample vaporization chamber 10 provided at the inlet of the column 18. A flow rate regulator 13 is provided in the carrier gas channel 12, and a constant flow rate of carrier gas (inert gas such as He) is supplied to the sample vaporizing chamber 10. The purge flow path 14 is for discharging an undesired gas released from the septum 11 made of silicon rubber or the like attached to the upper portion of the sample vaporizing chamber 10 from the sample vaporizing chamber 10. Since the purge flow path 14 is provided with a pressure sensor 15 and there is almost no flow path resistance between the pressure sensor 15 and the sample vaporization chamber 10, the gas pressure detected by the pressure sensor 15 is the sample vaporization chamber. 10 can be regarded as the gas pressure within 10 (that is, the inlet pressure of the column 18). The split flow path 16 is provided with an electromagnetic valve 17, and a sample to be introduced into the column 18 is discharged by discharging a predetermined ratio of carrier gas and the sample gas vaporized in the sample vaporization chamber 10 through the split flow path 16. Adjust the amount of.
[0003]
When a carrier gas having a constant flow rate determined by the split ratio (ratio of the gas flow rate flowing through the split flow path 16 to the total flow rate) is flowing through the column 18, the sample solution is injected into the sample vaporizing chamber 10 via the septum 11. The sample solution is vaporized and carried on the carrier gas stream to the column 18. While passing through the column 18, each component in the sample is temporally separated and sequentially detected by a detector 19 provided at the outlet of the column 18. The output signal of the detector 19 is amplified by the amplifier 20 and then input to the signal processing unit 21. The signal processing unit 21 converts the detection signals obtained sequentially into a digital value by an A / D converter, and creates a chromatogram based on this. Then, by analyzing each peak appearing in the chromatogram, qualitative and quantitative analysis of each component is executed. The display unit 23 displays chromatograms and results of quantification and qualitative analysis. FIG. 6A shows a part of the peak waveform of such a chromatogram.
[0004]
There are various types of noise that affect the chromatogram during the chromatographic analysis, but there are inherent noises (such as thermal noise) generated in electronic circuits such as the detector 19 and the amplifier 20, and external noise. The frequency of incoming noise etc. is relatively high. This type of noise is relatively large in a detector using a photo detector such as a flame photometric detector (FPD), and tends to become larger when an attempt is made to increase detection sensitivity. When such high-frequency noise exists, the peak waveform of the chromatogram is as shown in FIG. If the noise is recognized as the peak of the sample component, accurate analysis cannot be performed. Therefore, the signal processing unit 21 performs an appropriate filtering process to remove high-frequency noise before or when creating the chromatogram. Made.
[0005]
[Problems to be solved by the invention]
That is, since the frequency range of noise is higher than the frequency component of the peak waveform, only the high frequency range noise is removed using a low-pass filter. However, even when analyzing the same sample, the peak shape (that is, the frequency component of the peak) differs depending on chromatographic analysis conditions (for example, column inlet pressure, column dimensions, etc.). Needs to switch the cutoff frequency of the low-pass filter.
[0006]
Therefore, in the conventional gas chromatograph apparatus, the following two types of filter processing methods are used. One of them is that an analog filter whose time constant can be switched by a switch is provided between the amplifier 20 and the A / D converter of the signal processing unit 21, and can be appropriately selected by the operator's switch operation. The time constant of the filter can be changed. The other is to remove a waveform having a high-frequency component by digital signal processing, and the peak half-value width Wh (intensity is ½ of the peak value) shown in FIG. When a measurer inputs a threshold of (peak time width) as one of the signal processing conditions from the input setting unit 22, the signal processing unit 21 generates a pulse waveform having a half-value width equal to or smaller than the threshold when creating a chromatogram. We consider it as noise and remove it.
[0007]
However, the above-described filter switching operation and half-width setting must all be performed by the measurer through trial and error, which is not only time-consuming but also requires skill. Moreover, it is difficult for even an expert to set the filter cutoff frequency and half-value width optimally, and as shown in FIG. 6B, high frequency noise remains in the chromatogram and the S / N ratio deteriorates. On the contrary, as shown in FIG. 6 (c), the reading and tailing of the peak waveform spread, and there is a possibility that it becomes difficult to separate the adjacent peaks p1 and p2.
[0008]
The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a chromatographic signal processing apparatus capable of obtaining a good chromatogram by performing appropriate filter processing. There is.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a sample at a column outlet, in which a sample is placed in a gas or liquid mobile phase and circulated through the column, and each component in the sample that is separated and eluted in time is provided. In a signal processing device for a chromatograph to be detected by a detector,
d) a variable cutoff frequency filter that cuts off the high frequency range of the detector output signal;
e) Column dimensions, column oven temperature, column inlet pressure, carrier gas viscosity coefficient, column type, detector type, split ratio, thickness of stationary phase applied to the inner wall of the column, introduced into the sample vaporization chamber Determining means for determining a cutoff frequency of the filter in accordance with at least one of the amount of the sample solution to be obtained;
f) processing means for creating a chromatogram based on the signal processed by the filter;
It is characterized by having.
[0010]
Here, the conditions for chromatographic analysis are conditions that can affect the shape (steepness) of the peak waveform of the sample component during the analysis, or can affect the frequency band of high-frequency noise. For example, in a gas chromatograph, column dimensions, column oven temperature, column inlet pressure, carrier gas viscosity coefficient, column type, detector type, and split ratio in the case of split analysis, etc. is there.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the chromatograph signal processing apparatus according to the present invention, the determining means monitors the input set values of the analysis conditions necessary for the analysis, or monitors what is monitored at the time of analysis such as column oven temperature and column inlet pressure. Based on the value, the cutoff frequency is determined in consideration of the steepness (that is, the frequency) of the peak of the component eluted from the column and the frequency range of the high frequency noise, and the cutoff frequency is indicated to the filter. That is, for example, in a capillary column, the smaller the column inner diameter, the greater the number of separation stages, and each peak becomes steeper. Therefore, the cut-off frequency is made relatively high. The filter passes only the low frequency component of the output signal of the detector with the indicated cutoff frequency, and cuts off the high frequency region not related to the peak due to the sample component. Then, the processing means creates a chromatogram based on the signal from which undesired components in the high frequency range are removed.
[0012]
【The invention's effect】
Therefore, according to the chromatographic signal processing apparatus of the present invention, the output signal of the detector is filtered with the optimum cutoff frequency according to the analysis conditions and the like, so that the loss or deformation of the peak that appears due to the sample component is small, On the other hand, undesired high frequency noise generated by a detector or the like is accurately removed. As a result, a good chromatogram is obtained, so that the accuracy of qualitative and quantitative analysis performed based on the chromatogram is improved.
[0013]
In addition, since the operator himself / herself does not need to switch filters or input and set signal processing conditions in consideration of analysis conditions, etc., analysis can be performed efficiently and skill in such work can be obtained. No longer needed.
[0014]
【Example】
An embodiment of a chromatographic signal processing apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram centering on a signal processing unit of the gas chromatograph apparatus of the present embodiment. In this embodiment, the filter processing for removing high frequency noise is realized by a so-called digital filter.
[0015]
The detection signal of the detector 19 provided at the column outlet is amplified by the amplifier 20, converted into a digital signal by the A / D conversion unit 30 of the signal processing unit 21, and then given to the filter operation unit 31. Various kinds of analysis conditions as will be described later are input and set in the input setting unit 22 by the measurer, and the cut-off frequency determination unit 33 determines an appropriate cut-off frequency fc based on these analysis conditions and gives it to the coefficient calculation unit 32. . The coefficient calculation unit 32 calculates a coefficient of a digital filter having a predetermined configuration so that the cutoff frequency is instructed fc, and sets the coefficient in the filter calculation unit 31. The filter calculation unit 31 has a configuration of a low-pass digital filter, filters the digitized detection signal, and applies the filtered signal to the chromatogram creation unit 34.
[0016]
The filter calculation unit 31 is, for example, a well-known FIR filter, and may have the configuration shown in FIG. The input data xn is sequentially shifted for each sampling by the M delay elements 40, and the output data of each delay element 40 is multiplied by predetermined coefficients h0 to hM, respectively. The outputs of the multipliers 41 are added by an adder 42, and output data yn is taken out. As the basic configuration of such a filter, the order M and the sampling frequency are determined in advance, and the transfer characteristic, that is, the frequency characteristic can be changed by changing the values of the coefficients h0 to hM. The frequency characteristics by the filter calculation unit 31 are as shown in FIG. That is, at the cutoff frequency fc, the signal level is attenuated by 3 [dB] from the signal level in the low-frequency pass band. The filter operation unit 31 can be executed in a so-called software manner by causing a microcomputer centering on the CPU to execute a predetermined control program, or a shift register, a coefficient memory, a multiplier, an adder having a predetermined number of stages. It is also possible to configure in hardware using a device and a clock generation circuit.
[0017]
When the cutoff frequency fc is instructed, the coefficient calculation unit 32 calculates the coefficients h0 to hM by a predetermined calculation method. There are several well-known methods for calculating a coefficient from frequency characteristics, for example, a method using Fourier series expansion, a method using a window function (eg, Blackman window, Hamming window, etc.), and a Chebyshev approximation. (Reference: “Digital Filter Design” written by Masaaki Mitani, Shosodo). Although the ripple or the like of the frequency characteristic differs depending on which method is used, in any case, a filter coefficient that gives a predetermined frequency characteristic can be calculated.
[0018]
As shown in FIG. 3, the frequency characteristic of the filter operation unit 31 needs to be a characteristic that allows a peak having a relatively low frequency component to pass while removing noise having a relatively high frequency component. . Therefore, the cutoff frequency determination unit 33 determines the cutoff frequency as follows, for example. The peak shape corresponding to each sample component detected by the detector 19 is affected by various analysis conditions. In other words, the peak of the sample component becomes steep (frequency is high) under the following analysis conditions.
(1) The column inner diameter d is small.
(2) The column length L is short.
(3) The temperature T of the column oven is high.
(4) The column inlet pressure P is high.
(5) The split ratio r is large (the ratio of the sample introduced into the column is low).
(6) When the column is a capillary column, the thickness D of the stationary phase applied to the inner wall of the column is thin.
(7) The amount S of the sample solution injected into the sample vaporizing chamber is small.
[0019]
Thus, when the peak frequency is high, it is necessary to increase the cutoff frequency fc. These analysis conditions are usually input and set by the measurer from the input setting unit 22 prior to chromatographic analysis. Therefore, for example, a predetermined threshold value is appropriately determined in advance for each analysis condition as described above, and the input analysis condition is compared with the threshold value. Select either one. That is, the column inner diameter d, the column length L, the column oven temperature T, the column inlet pressure P, the split ratio r, the stationary phase thickness D, and the threshold values d1, L1, T1, P1, respectively defined for the sample injection amount S, If d ≧ d1, L ≧ L1, T ≦ T1, P ≦ P1, r ≦ r1, D ≧ D1, or S ≧ S1 with respect to r1, D1, and S1, then fc = fc1. On the other hand, when d <d1, L <L1, T> T1, P> P1, r> r1, D <D1, and S <S1, fc = fc2. Here, fc1 <fc2. When a column other than the capillary column is used, the thickness D of the stationary phase is ignored.
[0020]
Further, when it is desired to determine the cut-off frequency more precisely, for example, the cut-off frequency fc may be obtained based on a predetermined calculation formula as follows.
fc = fc0 · (k1 / d 2) · (k2 / L) · (k3 · T) · (k4 · P) · (k5 · r) · (k6 / D) · (k7 / S)
Here, k1 to k7 are predetermined constants. Such a constant is obtained in advance by experiments or the like and stored in a memory provided in the cutoff frequency determination unit 33. According to the above calculation formula, the cut-off frequency fc is high when the peak frequency is high, and conversely, the cut-off frequency fc is low when the peak frequency is low, depending on each analysis condition.
[0021]
In addition to the above analysis conditions, the peak may also be caused by the type of column, for example, a packed column (packed column), a hollow tube column (wide bore column), a capillary column, etc. The frequency of fluctuates. Therefore, it is preferable to consider such conditions as the type of column when determining the cutoff frequency fc.
[0022]
Furthermore, all the analysis conditions described above were factors that affect the peak frequency of each sample component passing through the column, but other factors that affect the frequency band of high-frequency noise such as the type of detector 19. Exists. Therefore, the type of detector 19 to be used (for example, a thermal conductivity detector, a flame photometric detector, an electron capture detector, etc.) may be input and set to change the cutoff frequency fc. When using a thermal conductivity detector, the steepness of the peak changes depending on the presence of the makeup gas and its flow rate.
[0023]
In the above-described embodiment, the cutoff frequency is determined using a numerical value or selection input and set by the measurer as the analysis condition. However, for example, the column inlet pressure P, the column oven temperature T, and the like are monitored by the pressure sensor 15 or a temperature sensor attached to the column oven during analysis. Therefore, such a monitor value can be used instead of using the value set as described above.
[0024]
Next, another embodiment of the chromatographic signal processing apparatus of the present invention will be described with reference to FIG. In the above embodiment, a digital filter is used, but in this embodiment, an analog filter is used. That is, an analog filter 50 is provided at the output stage of the amplifier 20, and the output signal of the filter 50 is converted into a digital signal by the A / D conversion unit 30 and input to the chromatogram creation unit 34. An analog filter 50 shown in FIG. 4 is a low-pass filter using an operational amplifier OP, has two capacitors C1 and C2 having different values, and switches the capacitors C1 and C2 by a relay RL. Thus, the cutoff frequency fc can be selected. Of course, the configuration of the analog filter 50 is not limited to this.
[0025]
The cut-off frequency determining unit 33 determines the cut-off frequency fc as in the above embodiment, and the relay driving unit 51 drives the relay RL so that the predetermined capacitors C1 and C2 are selected according to the cut-off frequency fc. Thereby, the frequency characteristics of the filter 50 are switched, and high frequency noise is effectively removed without significantly affecting the peak waveform.
[0026]
The above-described embodiment is an example, and it is obvious that changes and modifications can be made as appropriate within the scope of the present invention.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an embodiment of a chromatographic signal processing apparatus of the present invention.
FIG. 2 is a diagram illustrating an example of a configuration of a filter calculation unit in FIG. 1;
FIG. 3 is a diagram illustrating frequency characteristics of the filter of FIG. 2;
FIG. 4 is a configuration diagram of another embodiment of the chromatographic signal processing apparatus of the present invention.
FIG. 5 is a general configuration diagram of a gas chromatograph apparatus.
FIG. 6 is a diagram showing an example of a peak waveform of a chromatogram.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 18 ... Column 19 ... Detector 21 ... Signal processing part 22 ... Input setting part 30 ... A / D conversion part 31 ... Filter operation part 32 ... Coefficient operation part 33 ... Cutoff frequency determination part 34 ... Chromatogram preparation part 40 ... Delay element 41 ... multiplier 42 ... adder 50 ... analog filter 51 ... relay drive unit

Claims (1)

A signal processing device for a chromatograph in which a sample is placed in a gas or liquid mobile phase and circulated in the column, and each component in the sample that is separated and eluted is detected by a detector provided at the column outlet. In
a) a variable cutoff frequency filter that cuts off the high frequency range of the detector output signal;
b) Column dimensions, column oven temperature, column inlet pressure, carrier gas viscosity coefficient, column type, detector type, split ratio, thickness of stationary phase applied to the inner wall of the column, introduced into the sample vaporization chamber Determining means for determining a cutoff frequency of the filter in accordance with at least one of the amount of the sample solution to be obtained;
c) processing means for creating a chromatogram based on the signal processed by the filter;
A signal processing apparatus for chromatograph, comprising:

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