JP3767490B2 - Spectrophotometer and measurement signal correction method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spectrophotometer and a signal correction method for removing and correcting unnecessary components that are not analyzed from signals measured by a spectrophotometer or the like.
[0002]
[Prior art]
Analysis of a sample using a spectrophotometer such as FTIR is performed by comparing sample measurement data with background measurement data measured in the absence of the sample. That is, by dividing the sample measurement data by the background measurement data, information on components other than the sample is canceled, and thereby transmittance and absorbance representing sample characteristics can be obtained. However, in the process of dividing the sample measurement data by the background measurement data as described above, unnecessary component information other than the sample may not be completely canceled.
[0003]
Examples of unnecessary components other than the sample include water vapor and carbon dioxide in the atmosphere, and a technique for removing the influence of the water vapor and carbon dioxide has been developed. For example, there are known a method in which an optical system and a sample chamber are depressurized with a vacuum pump, and a method in which only unnecessary components are measured in advance and an influence of unnecessary components is removed from sample measurement data using this.
[0004]
In this method of removing the influence of unnecessary components, the transmittance representing the characteristics of the unnecessary components is obtained as a reference unnecessary component waveform, and the unnecessary component waveform included in the sample measurement data is expanded and contracted by expanding and contracting the reference unnecessary component waveform. Estimate and remove unnecessary components from the sample measurement data. As a method for obtaining the reference unnecessary component waveform, for example, the same measurement as that of the sample is performed on unnecessary components other than the sample such as water vapor and carbon dioxide in the atmosphere, and the water vapor and dioxide obtained by measurement without the sample are measured. There is known a method of obtaining information on unnecessary components such as carbon and data obtained by measuring in a state where unnecessary components are excluded by filling with nitrogen or the like, and dividing the former by the latter.
As another method for obtaining an unnecessary component waveform for reference, a method of theoretically calculating by using a data library having high-resolution spectral measurement information has been proposed.
[0005]
[Problems to be solved by the invention]
In the method of depressurizing the optical system and the sample chamber with a vacuum pump, there are problems such as an increase in the size of the device and a long measurement time. In order to obtain the unnecessary component waveform of the measurement, a large-scale device such as filling the device with nitrogen or complicated operation is necessary, so it is actually necessary to frequently perform this operation to update the unnecessary component waveform for reference This analysis is unrealistic.
[0006]
In addition, the waveform of unnecessary components is usually different when measurement conditions such as temperature and humidity are different. For this reason, in the method of obtaining the reference unnecessary component waveform by measurement in advance, a deviation occurs between the unnecessary component waveform included in the sample measurement and the reference unnecessary component waveform prepared in advance, and the correction accuracy deteriorates. There is a problem that it often occurs.
[0007]
Further, when the correction is performed using the reference unnecessary component waveform, it is necessary to perform the correction process after multiplying the reference unnecessary component waveform by a predetermined expansion / contraction ratio and matching the level with the sample measurement data. However, since there is a possibility that the peak position of the sample waveform and the peak position of the unwanted component are superimposed on the sample measurement data, it is not possible to calculate the correct expansion / contraction rate by simply comparing the waveform amplitude of both. Can not. Therefore, in order to estimate and remove unnecessary component waveforms in the sample measurement data using the reference unnecessary component waveform, it is necessary to repeat the work of inputting the expansion rate and checking the correction result visually. There is a problem that it is difficult to automatically calculate the expansion / contraction rate.
[0008]
Also, in the method of calculating the unnecessary component absorption waveform using high resolution library data, there are multiple factors that change the absorption waveform, such as component concentration, temperature, wave number deviation, optical system configuration, etc. in actual measurement, Since there is a need to consider these, a configuration for preparing a plurality of reference unnecessary component waveforms is required. Therefore, in order to solve the above-mentioned problem of correction accuracy in the correction method using the high resolution library data, all the waveform change factors and condition ranges necessary for obtaining a sufficient correction effect are comprehensively incorporated in advance. However, it is impossible to prepare all the various conditions in advance as described above, and use conditions and effects must be limited.
[0009]
In addition, in order to solve the problems of the automatic correction described above in the correction method using this high-resolution library data, pattern matching is repeatedly performed to gradually remove the influence of the sample absorption waveform, and the unnecessary component waveform for reference and the expansion / contraction rate Need to be determined. In this pattern matching, there are many processes that are considered to be highly dependent on measurement conditions and sample characteristics, such as the presence of a threshold parameter for determining whether the waveform is a sample waveform, and automation is sufficiently effective. The scenes obtained are considered limited. Therefore, an object of the present invention is to remove unnecessary component information from a spectroscopic measurement signal with high accuracy and to remove it stably and automatically.
[0010]
[Means for Solving the Problems]
According to the present invention, unnecessary component information of a spectroscopic measurement signal is accurately obtained by extracting a reference unnecessary component waveform representing characteristics of an unnecessary component from background measurement data, and the obtained reference unnecessary component waveform and sample measurement data are obtained. Is used to automatically calculate the expansion / contraction rate by calculating the expansion / contraction rate of the reference unnecessary component waveform, and to automate unnecessary component removal correction.
[0011]
The spectrophotometer of the present invention calculates a reference unnecessary component waveform calculating means for calculating a reference unnecessary component waveform from background measurement data, and calculates the expansion / contraction ratio of the reference unnecessary component waveform using the calculated reference unnecessary component waveform. And an unnecessary component removal correction unit that removes and corrects an unnecessary component from the sample measurement data using the calculated reference unnecessary component waveform and the calculated expansion / contraction rate.
[0012]
The measurement signal correction method of the present invention includes a step of calculating a reference unnecessary component waveform from background measurement data, a step of calculating an expansion / contraction ratio of the reference unnecessary component waveform using the calculated reference unnecessary component waveform, and And removing and correcting unnecessary components from the sample measurement data using the reference unnecessary component waveform and the expansion / contraction rate obtained in the above step.
[0013]
1 and 2 are a schematic diagram and a schematic waveform diagram for explaining the spectrophotometer and the measurement signal correction method of the present invention. In the measurement data (FIGS. 1 and 2A), the sample measurement data is data measured in a state where the sample exists, and the background measurement data is data measured in a state where the sample is excluded. Both sample measurement data and background measurement data contain unnecessary components such as water vapor and carbon dioxide.
[0014]
The reference unnecessary component waveform (FIGS. 1 and 2D) is an unnecessary component waveform used as a reference for removing and correcting unnecessary components included in the sample measurement data, and is not required in the background measurement data. Represents the absorption characteristics of the component. In the present invention, the reference unnecessary component waveform calculation means 1 obtains the outer contour of the background measurement data (FIG. 2B) and divides the background measurement data by the value of the outer contour to thereby remove the reference unnecessary component. Calculate the waveform.
[0015]
The reference unnecessary component waveform to be calculated represents the transmittance of the unnecessary component, and the value is a ratio. Therefore, in order to remove and correct the unnecessary component of the sample measurement data with the reference unnecessary component waveform, it is adjusted to the size of the measurement data value. There is a need. The expansion / contraction rate is a ratio for adjusting the reference unnecessary component waveform to the size of the measurement data value.
[0016]
The expansion / contraction rate calculation means 2 uses the waveform in which the unnecessary component of the measurement data value is not absorbed as the target correction value (FIG. 2C), and divides the measurement data value by the target correction value for each peak of the reference unnecessary component waveform. Thus, the depth A of the absorption peak of the measurement data is obtained, and the individual expansion / contraction ratio is calculated by obtaining (LogA / LogB) from this value by the depth B of the absorption peak of the unnecessary component waveform for reference (FIG. 2 ( e)). The individual expansion / contraction rate obtained by this calculation is an individual value at each peak of the reference unnecessary component waveform, and the expansion / contraction rate varies depending on the superposition state of the unnecessary component and the sample component on the sample measurement data. Since the expansion / contraction ratio of the unnecessary component cannot be accurately calculated from the portion where the sample waveform is superimposed, the expansion / contraction ratio calculation means 2 preferentially uses the unnecessary component waveform information without the superposition of the sample waveform, and the reference unnecessary component. The expansion / contraction ratio for the waveform measurement data is calculated, and the reference unnecessary component waveform is expanded / contracted using the expansion / contraction ratio.
[0017]
One aspect of obtaining the expansion / contraction ratio from the individual expansion / contraction ratio is to calculate the median which is the median value of the individual expansion / contraction ratio, and the other aspect is to calculate the median having a value weighted to the individual expansion / contraction ratio. As the weight used for this weighting, a value obtained by standardizing the value of the reference unnecessary component waveform from 0 to 1 can be used so that the larger the absorption of the unnecessary component, the closer to 1. Weighting with this load increases the contribution of the absorption peak of the unnecessary component and decreases the contribution of the absorption peak of the sample, and thereby, the expansion / contraction rate of the unnecessary component is accurately calculated even if the sample waveform is superimposed.
[0018]
The unnecessary component waveform removal correction unit 3 obtains an unnecessary component by matching the size of the reference unnecessary component waveform with the size of the measurement data using the expansion / contraction rate calculated by the expansion / contraction rate calculation unit 2, and calculates the calculated unnecessary component. Removal correction is performed from the sample measurement data (FIGS. 1 and 2 (f)).
[0019]
In addition, the expansion / contraction rate has the expansion / contraction rate with respect to sample measurement data, and the expansion / contraction rate with respect to background measurement data, and correct | amends sample measurement data and background measurement data using each expansion / contraction rate. Here, the expansion / contraction rate with respect to the background measurement data is always 1 because the correction target value of the background measurement data becomes the reference unnecessary component waveform itself, and the background measurement data correction obtained by correcting using the expansion / contraction rate is performed. The result is the reference unnecessary component waveform itself.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 3 is a schematic diagram for explaining measurement signal correction according to the present invention. In FIG. 3, a measuring means 4 such as a spectrophotometer such as FTIR obtains sample measurement data by measuring in the presence of the sample, and obtains background measurement data by measuring in a state without the sample. obtain. Note that both the sample measurement data and the background measurement data contain unnecessary components such as water vapor and carbon dioxide.
[0021]
The reference unnecessary component waveform calculating means 1 calculates the reference unnecessary component waveform using the background measurement data, and the expansion / contraction rate calculating means 2 calculates the expansion / contraction rate of the reference unnecessary component waveform using the calculated reference unnecessary component waveform. Calculate. The reference unnecessary component waveform to be calculated represents the transmittance of the unnecessary component, and the value is a ratio. Therefore, in order to remove and correct the unnecessary component of the sample measurement data by the reference unnecessary component waveform, it is adjusted to the size of the measurement data value. There is a need. The expansion / contraction rate is a ratio for adjusting the reference unnecessary component waveform to the size of the measurement data value.
[0022]
The expansion / contraction rate calculation means 2 can calculate the expansion / contraction rate for the sample measurement data and the expansion / contraction rate for the background measurement data. Calculation of expansion / contraction rate for sample measurement data is performed using sample measurement data, target correction value in sample measurement, and reference unnecessary component waveform, and calculation of expansion / contraction rate for background measurement data is performed by background measurement and background measurement. Using the target correction value and the reference unnecessary component waveform.
[0023]
The unnecessary component removal correcting unit 3 removes and corrects the unnecessary component from the sample measurement data using the reference unnecessary component waveform and the expansion / contraction rate obtained by the expansion / contraction rate calculating unit 2.
Here, when the unnecessary component waveform for reference is obtained from the outer contour of the background measurement data, the target correction value in the background measurement is the same as the outer contour of the background measurement data. Always 1, the background measurement data correction result obtained by the unnecessary component removal correction means 3 is the same as the reference unnecessary component waveform. Therefore, it is possible to omit processing for obtaining the expansion / contraction ratio for the background measurement data and the background measurement data correction result. In FIG. 3, parts that can be omitted are indicated by broken lines and underlines.
The transmittance and absorbance calculation means 5 calculates the transmittance and absorbance using the sample measurement data correction result and the background measurement data correction result (unnecessary component waveform for reference) obtained by the unnecessary component removal correction means 3.
[0024]
The flowchart shown in FIG. 4 shows a processing procedure according to the present invention. In addition, the code | symbol which begins with S shown in FIG. 3 respond | corresponds to each process of a flowchart.
First, the reference unnecessary component waveform is calculated from the background measurement data by the reference unnecessary component waveform calculating means 1 (step S1). Next, the expansion / contraction ratio for the sample measurement data is calculated by the expansion / contraction ratio calculation means 2 using the reference unnecessary component waveform (step S2), and the unnecessary component waveform correction correction for the sample measurement data is further performed by the unnecessary component removal correction means 3. Is performed (step S3).
[0025]
Similarly, with respect to the background measurement data, the expansion / contraction ratio is calculated by the expansion / contraction ratio calculation means 2 (step S4), and the expansion / contraction ratio is calculated by the unnecessary component removal correction means 3 (step S5), and then the unnecessary component waveform is calculated. Is removed and corrected (step S6).
[0026]
Note that when the outer contour is used as the background measurement data correction result, the steps S4 and S5 (steps surrounded by a broken line) can be omitted.
Hereinafter, each processing content of the reference unnecessary component waveform calculation unit, the expansion / contraction rate calculation unit, and the unnecessary component removal correction unit will be described.
[0027]
FIG. 5 is a waveform example of data of background measurement data (Background Power) and sample measurement data (Sample Power) measured by the spectrophotometer. As can be seen from the waveform shown in FIG. 5, absorption waveforms of water vapor and carbon dioxide, which are atmospheric components, exist in both background measurement data and sample measurement data. For example, absorption by water vapor is observed in waveforms (circles) having wave numbers 1300 to 2000 and wave numbers 3500 to 4000 (1 / cm).
The reference unnecessary component waveform calculating means 1 calculates a reference unnecessary component waveform from the background measurement data. FIG. 6 shows a flowchart for calculating the reference unnecessary component waveform.
[0028]
The reference unnecessary component waveform calculating means 1 first extracts the outer contour of the background measurement data. Specifically, the extraction of the outer contour can be performed by the following steps 1 to 3.
In step 1, a point at which the gradient of the background measurement data changes from negative to positive is searched, thereby detecting all peak top points of the background measurement data.
In step 2, the value of a point between adjacent peak top points is replaced with an interpolated value using the values of the peak top points on both sides.
[0029]
In step 3, steps 1 and 2 are repeated until the total peak top interval is equal to or greater than a specific value. The specific value of the peak top interval used in step 3 is designated in advance so that the absorption peak is filled by interpolation according to the unnecessary component waveform to be removed and corrected. FIG. 7 shows the outer contour extraction result. This is an approximate representation of the waveform shape of the spectrophotometer measurement data when there is no light absorption due to unnecessary components, and becomes an envelope (step S11).
[0030]
Next, a reference unnecessary component waveform is calculated by dividing the background measurement data value by the extracted value of the outer contour. This reference unnecessary component waveform shows the absorption characteristics of the unnecessary component in the background measurement data.
When the background measurement data is Back Power [k] and the outer contour calculation result is Outline [k] (k = 0, 1, 2,...), The calculation formula for the reference unnecessary component waveform RefTrs [k] is The following formula. Note that k represents the position of the peak top point.
[0031]
RefTrs [k] = BackPower [k] / Outline [k] (1)
FIG. 8 shows a calculation result example of the reference unnecessary component waveform. This calculation result indicates the transmittance of the unnecessary component, and the transmittance of the portion without the unnecessary component is 1 (step S12).
Next, the expansion / contraction rate calculating means 2 calculates the expansion / contraction rate of the reference unnecessary component waveform with respect to the sample measurement data or the background measurement data. FIG. 9 shows a flowchart for calculating the expansion / contraction ratio.
[0032]
The expansion / contraction rate calculation means 2 first calculates a correction target value. Since the target waveform is a waveform that does not absorb unnecessary components, it is obtained by extracting the outer contour of the target data. The extraction of the outer contour can be the same as the extraction of the background outer contour described above. FIG. 10 shows a calculation example of the target correction value for the sample measurement data (step S21).
[0033]
Next, the wave number position where the reference unnecessary component waveform reaches a peak is extracted. The wave number position can be extracted, for example, by extracting the peak bottom by detecting the position where the slope of the reference unnecessary component waveform changes from negative to positive (step S22).
[0034]
Furthermore, the individual expansion / contraction rate and the load are calculated at each extracted peak wave number position. The calculation of the individual expansion / contraction rate and the load is, for example, at the wave number position of each peak, the data value is Power [p], the reference unnecessary component waveform value is RefTrs [p] (p = 0, 1, 2,... ) If the correction target value is Target [p], the individual expansion / contraction rate Factor [p] and the load Weight [p] can be calculated by the following equations.
[0035]
Factor [p] = Log (Power [p] / Target [p]) / Log (RefTrs [p]) (2)
Weight [p] = | 1.0−RefTrs [p] | (3)
FIG. 11 shows an example of calculation results of the individual expansion / contraction rate and load. The above equation (2) is determined by the depth of the absorption peak of the sample measurement data and the depth of the absorption peak of the reference unnecessary component waveform. If the unnecessary component and the sample component do not overlap on the sample measurement data, the wave number A substantially constant value is calculated regardless of the position. For example, a section indicated by an arrow in FIG. 10 is a section in which the individual expansion / contraction rate is a substantially constant value, and this section can be regarded as a sample component.
[0036]
On the other hand, if the unnecessary component and the sample component are overlapped, different individual expansion / contraction ratios are calculated, for example, as indicated by the circles in the calculation example of the individual expansion / contraction ratio and load shown in FIG. The load indicates the degree of superimposition of the unnecessary component on the sample component. Weight [p] shown in the above equation (3) is a value normalized from 0 to 1, and the greater the absorption of the unnecessary component, A close value is large (step S23).
Finally, using the calculation results of the individual stretch rate and load, eliminate the value of the individual stretch rate that is considered to have sample overlap, and obtain the average value of the individual stretch rate that is considered to have no overlap. To decide.
[0037]
The stretch rate is determined by, for example, calculating the median of each individual stretch rate calculated by the above equation (2). The distribution of the individual expansion / contraction rate is considered to be a small number of places where the sample components are considered to be superimposed, for example, as indicated by the circles in FIG. Therefore, by calculating the median of the individual expansion / contraction ratios, the median value of each individual expansion / contraction ratio is obtained, the influence of a small number of extraneous values is eliminated, and the average value indicated by a large number of elements of the unnecessary component group is calculated. .
[0038]
In the calculation of the expansion / contraction rate by calculating the median of the individual expansion / contraction rate, the weighted median is calculated by weighting each individual expansion / contraction rate with the load calculated by the above equation (3). In addition to calculating the normal median, weighting with the load of equation (3) increases the contribution of the peak that absorbs unnecessary components, reducing the risk that the sample peak superimposing element contributes to the calculation of the expansion / contraction rate. can do. FIG. 12 is a diagram for explaining the weighting of the load. FIGS. 12A and 12B schematically show a histogram showing the distribution of the number of peaks when the weight is not weighted and when the weight is weighted, and a histogram showing the distribution of the weight integrated value. . As shown in FIG. 12 (b), by weighting the load, the relative magnitude between the contribution of the individual stretch rate due to the sample peak and the contribution of the individual stretch rate due to the unnecessary component is changed, and the unnecessary component is changed. The contribution due to can be increased and extracted (step S24).
[0039]
The unnecessary component removal correction means 3 performs unnecessary component removal correction processing on the sample measurement data or background measurement data using the reference unnecessary component waveform and the calculated expansion / contraction rate. Note that when the reference unnecessary component waveform is used as the background measurement data correction result, the unnecessary component removal correction processing for the background measurement data can be omitted.
[0040]
Assuming that the correction result data Power ′ is the reference unnecessary component waveform RefTrs, the expansion / contraction rate s, and the specified measurement data Power, the individual expansion / contraction factor Factor [p] corresponds to the expansion / contraction rate s in equation (2), and correction is performed. The target value Target [p] is calculated by the following equation (4) by making it correspond to the correction result data Power ′.
Power ′ [k] = Power [k] / (RefTrs [k]) ^s (4)
Note that k = 0, 1, 2,.
[0041]
FIG. 13 shows an example of the result obtained by removing the water vapor component and correcting the sample measurement data and the background measurement data shown in FIG. In the figure, the waveform indicated by Corrected Sample Power indicates an example of the correction result of the sample measurement data, and the waveform indicated by Corrected Back Power indicates an example of the correction result of the background measurement data.
[0042]
FIG. 14 shows a comparative example of the transmittance (indicated by Corrected in the figure) calculated from the removal correction result and the transmittance (indicated by Org in the figure) directly calculated from the measurement data.
In the above description, for the sake of simplicity, an example of correction for removing water vapor components is shown. However, the present invention is not a method effective only for water vapor, and the target wave number region and the peak top interval at the time of outer contour extraction are specified. By changing the value, it can also be applied to the removal correction of carbon dioxide and other unnecessary components.
[0043]
According to the aspect of the present invention, an unnecessary component waveform for reference is extracted from background measurement data whose measurement conditions are considered to be similar to that of sample measurement and used for correction. Applicable correction is possible, and unnecessary component waveforms can be removed with high accuracy.
[0044]
Further, according to the aspect of the present invention, in the calculation of the expansion / contraction ratio, the condition that the unnecessary component peak on which the sample is not superimposed is numerically superior to the unnecessary component peak on which the sample is superimposed is almost constantly satisfied. By using it, the influence of the sample superposition peak is eliminated. Since this process can be performed without using a specific measurement condition, a threshold value depending on the sample, and the like, a stable and accurate automatic process is possible, and the operation is simplified.
[0045]
【The invention's effect】
As described above, according to the present invention, unnecessary component information of a spectroscopic measurement signal can be accurately removed, and can be stably and automatically removed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining a spectrophotometer and a measurement signal correction method of the present invention.
FIG. 2 is a schematic waveform diagram for explaining a spectrophotometer and a measurement signal correction method of the present invention.
FIG. 3 is a schematic diagram for explaining measurement signal correction according to the present invention.
FIG. 4 is a flowchart for explaining a processing procedure according to the present invention.
FIG. 5 is a waveform example of data of background measurement data (Background Power) and sample measurement data (Sample Power).
FIG. 6 is a flowchart for explaining calculation of an unnecessary component waveform for reference according to the present invention.
FIG. 7 is a diagram illustrating an outer contour extraction result according to the present invention.
FIG. 8 is a diagram showing a calculation result example of a reference unnecessary component waveform according to the present invention.
FIG. 9 is a flowchart for explaining the calculation of the expansion / contraction rate according to the present invention.
FIG. 10 is a diagram showing a calculation example of a target correction value for sample measurement data according to the present invention.
FIG. 11 is a diagram illustrating a calculation example of an individual expansion / contraction rate and a load according to the present invention.
FIG. 12 is a diagram illustrating weighting of a load according to the present invention.
FIG. 13 is a diagram showing an example of a water vapor component removal correction result for sample measurement data and background measurement data according to the present invention.
FIG. 14 is a diagram showing a comparative example of the transmittance calculated from the removal correction result and the transmittance directly calculated from the measurement data.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Reference unnecessary component waveform calculation means, 2 ... Expansion / contraction rate calculation means, 3 ... Unnecessary component removal correction means, 4 ... Measurement means, 5 ... Transmission factor, Absorbance calculation means.

Claims (2)

Reference unnecessary component waveform calculation that calculates a reference unnecessary component waveform using background measurement data including water vapor or carbon dioxide, which is an unnecessary component, and a background that does not include the unnecessary component calculated from the background measurement data. Means,
An expansion / contraction rate calculating means for calculating an expansion / contraction rate for adjusting the unnecessary component waveform for reference to the size of the sample measurement data;
A spectrophotometer comprising: an unnecessary component removal correction unit that removes and corrects an unnecessary component from sample measurement data using the reference unnecessary component waveform obtained by expanding and contracting the reference unnecessary component waveform at the expansion / contraction ratio. Total. A signal correction method for removing unnecessary component information from a spectroscopic measurement signal,
Calculating a reference unnecessary component waveform using background measurement data including water vapor or carbon dioxide, which is an unnecessary component, and a background not including the unnecessary component calculated from the background measurement data;
Calculating an expansion / contraction ratio for adjusting the unnecessary component waveform for reference to the size of the sample measurement data;
A step of expanding / contracting the reference unnecessary component waveform obtained in the step by the expansion / contraction ratio obtained in the step, and removing and correcting the unnecessary component from the sample measurement data using the contracted reference unnecessary component waveform. A measurement signal correction method.

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