JP2792175B2 - Analysis method by X-ray diffraction - Google Patents

Description

The present invention relates to an analysis method using an X-ray diffraction method, and particularly to an analysis method suitable for analysis of a substance having a large number of peaks in an X-ray diffraction image such as an organic compound. About.

(Prior art) In principle, qualitative analysis using X-ray diffraction is based on the publication of standard data that collects data on the position and intensity of diffraction lines for many substances. The diffraction image is analyzed to determine the position and intensity of the peak and to collate it with the above standard data.

In this case, it is a very difficult task to check each peak for data of many kinds of candidate substances in the case of a large number of diffraction lines (40 or more on average per substance) such as organic compounds. Yes, when matching is performed on individual peaks, the peak position shifts due to the influence of the slight orientation of the sample, so errors in matching are likely to occur, and matching errors are also likely to occur, and the reliability of qualitative results is low. Become. However, there has been no special collation search method even in such a case.

(Problems to be Solved by the Invention) An object of the present invention is to improve the efficiency and reliability of the operation of collating an X-ray diffraction image of a sample in which many diffraction lines appear with standard data.

(Means for Solving the Problems) A function display that connects the vertices of each diffraction line peak of the X-ray diffraction image of the unknown sample to be fixed is created, and each diffraction is performed based on the standard data of the candidate substance to be compared in the standard data. Create a function display that links the line vertices, and display the function display of the unknown sample,
The function display of the candidate substance to be compared is collated with the above function display, and a substance having the smallest difference between the two as the whole function is searched.

(Action) FIG. 1A is a measured X-ray diffraction image of a sample, and FIG. 1B is obtained by analyzing the diffraction image of A and obtaining and displaying the position of the diffraction line, that is, the diffraction angle 2θ and the diffraction line intensity. Is a function connecting the vertices of the diffraction line. FIG. 1C is data of standard data of a candidate substance to be collated, and curve C in FIG. 1C is a function connecting the vertices of each diffraction line of this data. FIG. 1D
Is the difference between the functions B and C. The present invention searches for a substance in which this difference is the smallest as a whole. Between the measured X-ray diffraction image of a substance and the data in the standard data, there is a slight difference in the position and intensity between the corresponding peaks due to the temperature at the time of the measurement and the slight internal strain of the sample. Therefore, even if the bar-shaped patterns shown in FIGS. 1B and 1C are overlapped, perfect coincidence is usually not found. Many substances show similar arrangement of diffraction lines. It is not clear how well they match as a whole when compared book by book. Since the present invention compares the curves connecting the vertices of the diffraction lines, if the sample and the reference substance are the same, the slightest difference in the position or intensity of the individual diffraction lines is offset as a whole, and the difference between the two curves is Will be minimal. In this comparison operation, the difference between the two curves is obtained not continuously for each diffraction line position but continuously in the direction of the variable 2θ (when using a computer, at an appropriately small interval irrelevant to the diffraction line position). The operation is greatly simplified, it is the most suitable method for automatic calculation, and the efficiency of the overall diffraction pattern Since the identification is performed with a good match, the accuracy of the identification is also increased.

(Embodiment) FIG. 2 shows a flowchart of an operation for executing the method of the present invention. In step (a), an X-ray diffraction image of the sample is actually measured to obtain data as shown in FIG. 1A. Next, the background is subtracted from the measured data, and Kα1, Kα
The peaks based on the two lines are separated and data processing such as detection of the center of the peak is performed to obtain the diffraction line pattern of FIG. 1B (b), and a continuous function connecting the vertices of this diffraction line is obtained. Make curve B (c). The method of creating this function is as follows. Each diffraction peak is centered on the diffraction line position 2θ = x, and its height h
Is represented by a Gaussian distribution function having the vertex as a vertex, and one continuous curve is created as the sum of the functions. The function used here need not be a Gaussian distribution function, but may be any other suitable function such as a spline function. Next, several candidate substances expected for the sample are selected from the standard data base that accumulates the diffraction image data of various substances, and the data of the diffraction images are extracted (d). In the same manner as in the step (c), a continuous function connecting the diffraction line vertices is created (e). Next, the function obtained in step (c), the curve function B (x) in FIG. 1B,
(E) the squared integral of the difference I from the curve function of FIG. Is calculated (to). The integration range is a range where the diffraction image exists. The operation (f) is performed for each candidate substance, the candidate substance giving the smallest value of the obtained integral I is identified (g) as the sample substance, and the operation is completed. Needless to say, the above operation (f) determines the degree of coincidence between the function of the sample and the function of the candidate substance by the least square method.

When making a continuous curve connecting the diffraction line vertices in each of the steps (c) and (e), the relative intensity is used as the intensity of the diffraction line.
To determine other diffraction line intensities. Also, as a candidate substance, all substances belonging to a certain group are collected, and the 50 substances are arranged and printed out in order from the one with the smaller value of the integral I, and the final identification work is performed by referring to various other data. It ends.

(Effect of the Invention) In the present invention, since the comparison of X-ray diffraction lines is performed quantitatively and there is no room for subjectivity at all, and the diffraction images are compared as a whole,
The influence of the position of each diffraction line or the deviation of the intensity is small, and when there are many diffraction lines, it is remarkably efficient and qualitative at high speed as compared with collation for each individual diffraction line. Therefore, it becomes possible to handle a large number of substances as identification candidates, and the accuracy of identification becomes extremely high.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the outline of the present invention, and FIG. 2 is a flowchart showing the procedure of an operation for executing the method of the present invention.

Claims (1)

(57) [Claims] 1. A function display that connects the peaks of each diffraction line of an actually measured X-ray diffraction image of a sample is prepared, and a function display that connects the peaks of each diffraction line of the candidate substance for identification is prepared based on standard data. An analysis method by X-ray diffraction, which searches for a candidate substance having the smallest difference as a whole.