JP4523958B2 - X-ray fluorescence analyzer and program used therefor - Google Patents

Description

  The present invention relates to a fluorescent X-ray analyzer that analyzes the composition and area density of a sample by the FP method and a program used therefor.

  Conventionally, there is an X-ray fluorescence analyzer that analyzes a composition and an area density of a sample using a fundamental parameter method (hereinafter referred to as FP method). In the FP method, the theoretical intensity of secondary X-rays generated from each element in a sample is calculated based on the assumed composition, that is, the concentration of the element, and the theoretical intensity and the measured intensity measured by the detection means (the background component is calculated). The calculated concentration of the element is approximated and corrected so that the calculated measured intensity converted to the theoretical intensity scale is the same as the subtracted net intensity), and the element concentration (analytical value), that is, the composition in the sample is calculated. Calculate (for example, refer to Patent Documents 1 and 2).

  Here, a detection limit is required for the analysis target element together with the concentration, and the detection limit is not only the detected element, that is, the detection element included in the calculated composition, but also the element that was not detected, that is, the measurement intensity is 0 and the concentration. Is also required for non-detectable elements not substantially included in the calculated composition. This is to report that the actual concentration is less than the specified regulation value for each element by reporting the detection limit for the non-detectable element.

For example, in the calibration curve method, the detection limit LLD is obtained by multiplying the calibration curve gradient k by 3 times the statistical variation σ _B of the measured intensity for the blank sample not containing the target element.

LLD = 3 kσ _B (1)

The FP method does not have the concept of a calibration curve, but for the detected elements, the calibration curve gradient can be calculated from the calculated concentration and measured intensity, and the measured intensity of the background instead of the statistical fluctuation of the measured intensity for the blank sample Since the statistical fluctuations can be calculated, the detection limit can be calculated.
JP 2000-097885 A JP 2006-343112 A

  However, since the measured intensity and the calculated concentration are 0 for the non-detectable element, the calibration curve gradient cannot be calculated and the detection limit cannot be calculated. Therefore, the composition is calculated by the FP method by adding the measured intensity corresponding to an appropriate trace concentration that does not affect the analytical value calculation result of the detected element for the non-detected element to the actually measured measured intensity. It is conceivable that the trace limit is obtained by calculating the calibration curve gradient of the non-detected element from the added measured intensity and the obtained trace concentration to calculate the detection limit. However, since the measurement intensity per unit concentration varies greatly depending on the size and composition of the sample, the FP method that handles various samples cannot estimate the measurement intensity to be applied to each sample. If the concentration corresponding to the intensity is too high, the analysis value calculation result of the detected element is different from the case where the concentration of the non-detected element is 0.

  The present invention has been made in view of the above-mentioned conventional problems. In the X-ray fluorescence analyzer for analyzing the composition and area density of a sample by the FP method and a program used therefor, it is possible to accurately calculate the detection limit for a non-detectable element. The purpose is to provide.

In order to achieve the above object, the first configuration of the present invention first assumes an X-ray source that irradiates a sample with primary X-rays, and a detection means that measures the intensity of secondary X-rays generated from the sample. Based on the measured composition, the theoretical intensity of secondary X-rays generated from each element in the sample is calculated, and the theoretical intensity and the measured intensity measured by the detection means agree with the converted measured intensity converted to the theoretical intensity scale. Thus, the X-ray fluorescence analysis apparatus includes a computer as a calculation means for calculating the composition of the sample by sequentially correcting and calculating the assumed composition. Then, for the non-detectable elements not included in the calculated composition, the calculation means assumes a composition for calculating the detection limit by adding a predetermined trace concentration, and based on the composition for calculating the detection limit, the non-detectable element Calculate the theoretical intensity of the secondary X-rays generated from the non-detectable element from the theoretical intensity of the non-detectable element and the device sensitivity coefficient previously determined for conversion between the theoretical intensity and the measured intensity. Calculate the estimated measurement intensity, calculate the calibration curve slope of the non-detection element from the estimated measurement intensity of the non-detection element and the predetermined trace concentration, and measure the background measurement intensity of the non-detection element measured by the detection means From this, the statistical fluctuation of the background of the non-detectable element is calculated, and the detection limit of the non-detectable element is calculated from the statistical fluctuation of the background of the non-detectable element and the calibration curve slope of the non-detectable element. To.

  According to the apparatus of the first configuration, for a non-detection element, a predetermined trace concentration that does not affect the composition, that is, the concentration of the detection element, is assumed, and the detection limit calculation composition added to the calculated composition is used. Since the detection limit is calculated based on this, the detection limit of the non-detection element can be accurately calculated for individual samples having different sizes and compositions.

  A second configuration of the present invention is a program for causing a computer included in the device of the first configuration to function as the calculation unit. The same effect as the apparatus of the first configuration can be obtained by the program of the second configuration of the present invention.

  Hereinafter, an X-ray fluorescence analyzer according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, this apparatus generates from a sample stage 8 on which a sample 13 is placed, an X-ray source 1 such as an X-ray tube that irradiates the sample 13 with primary X-rays 2, and the sample 13. And detecting means 9 for measuring the intensity of secondary X-rays 4 such as fluorescent X-rays and scattered rays. The detection means 9 includes a spectroscopic element 5 that splits secondary X-rays 4 generated from the sample 13 and a detector 7 that measures the intensity of each of the split secondary X-rays 6. Note that a detector with high energy resolution may be used as the detection means without using the spectroscopic element 5.

  Based on the assumed composition, that is, the concentration of the element, the theoretical intensity of the secondary X-ray 4 generated from each element in the sample 13 is calculated, and the theoretical intensity and the measured intensity measured by the detecting means 9 are calculated based on the theoretical intensity scale. The calculation means 10 for calculating the concentration of the element in the sample 13, that is, the composition, is obtained by successively correcting the assumed element concentration so that the converted measurement intensity converted into the same value.

  After calculating the composition of the sample, the calculation means 10 calculates a detection limit for the non-detection elements not included in the calculated composition by the following procedure. First, a predetermined trace concentration is added to the non-detectable element, and the composition for calculating the detection limit is assumed by subtracting other elements (for example, the element with the maximum concentration) from the composition calculated for the added trace concentration. Then, based on the composition for calculating the detection limit, the theoretical intensity of the secondary X-ray 4 generated from the non-detectable element is calculated. Next, the estimated measured intensity of the non-detected element is calculated from the theoretical intensity of the non-detected element and the device sensitivity coefficient obtained in advance for conversion between the theoretical intensity and the measured intensity. Next, a calibration curve gradient of the non-detection element is calculated from the estimated measurement intensity of the non-detection element and the predetermined trace concentration. Next, the statistical fluctuation of the background of the non-detected element is calculated from the measured intensity of the background of the non-detected element measured by the detection means 9. Then, the detection limit of the non-detectable element is calculated from the statistical fluctuation of the background of the non-detectable element and the calibration curve gradient of the non-detectable element.

  This X-ray fluorescence analyzer operates as follows. The sample 13 placed on the sample stage 8 is irradiated with the primary X-ray 2 from the X-ray source 1, and the generated secondary X-ray 4 is incident on the spectroscopic element 5, and the dispersed secondary X-ray 6 is obtained. The intensity is measured by the detector 7 every time. And the calculation means 10 calculates the composition of the sample 13 by the conventional FP method. More specifically, the theoretical intensity of the secondary X-ray 4 generated from each element in the sample 13 is calculated based on the assumed composition, that is, the element concentration, and the theoretical intensity and the measured intensity measured by the detection means 9 ( The assumed element concentration is successively approximated and calculated so that the converted measured intensity converted to the theoretical intensity scale (the net intensity minus the background) matches the element concentration in the sample 13, that is, the composition. calculate.

  At this time, after the calculation means 10 calculates the composition of the sample, it detects not only detected elements included in the calculated composition but also non-detected elements not included in the calculated composition by the following procedure. The limit is calculated and displayed on the display (not shown) together with the composition.

First, in advance, it is defined by the following equation (2), has been required a device sensitivity coefficient K for the conversion between the theoretical strength I _T and the measured intensity I _M, it calculating means 10 stores Yes.

I _M = K I _T (2)

For the detection element i, the calibration curve gradient k is calculated from the calculated concentration W _i and the measured intensity I _iM measured by the detection means 9 by the following equation (3).

k = W _i / I _iM (3)

Further, the statistical variation σ _B of the background measurement intensity measured by the detection means 9 is calculated as follows. For example, in the case of measuring the background at two points before and after the peak in a wavelength dispersive X-ray fluorescence spectrometer, first, the measured intensity, which is the net intensity I _Net (= I _iM ), is expressed by the following equations (4), (5 )

_{I Net = I P -I B (} 4)

I _B = k1 × I _B1 + k2 × I _B2 (5)

_Here, the net intensity after _{I Net} background removal (kcps), _{I P} is the X-ray intensity or peak intensity of the peak position P (kcps), _{I B} is calculated background intensity _{(kcps), I B1,} I _B2 background X-ray intensity of the measuring positions B1, B2 (kcps), k1 , k2 are the background subtraction factor.

If the measurement times at the peak position P and the background measurement positions B1 and B2 are T _P , T _B1 , and T _B2 , respectively, the statistical fluctuation σ _Net of the net intensity is calculated by the following equation (6).

In the blank sample containing no purpose _element, because it is I P = _{I B,} equation (6) is given by the following equation (7).

As this σ _B , the statistical fluctuation of the measured intensity of the background is calculated. When the background is measured at only one point, the term _IB2 is not used in the equations (5) to (7).

From the calibration curve gradient k calculated by the equation (3) and the statistical fluctuation σ _B of the background measurement intensity calculated by the equation (7), the detection limit LLD (= 3 kσ _B ) of the detection element is calculated by the equation (1). Is calculated.

For the non-detectable element i, first, a predetermined trace concentration W _i (for example, 1 ppm) is added, and other elements (for example, elements having the maximum concentration) are reduced in the composition calculated for the added trace level concentration W _i. Thus, assuming the composition for calculating the detection limit, the theoretical intensity I _iT of the secondary X-ray (fluorescent X-ray) 4 generated from the non-detectable element is calculated based on the composition for calculating the detection limit.

Next, an estimated measured intensity I _iM (= KI _iT ) corresponding to a predetermined trace concentration W _i is calculated from the theoretical intensity I _iT of the non-detectable element and the device sensitivity coefficient K by Equation (2).

Next, a calibration curve gradient k (= W _i / I _iM ) of the non-detectable element is calculated from the estimated measurement intensity I _iM of the non-detectable element and a predetermined trace concentration W _{i according} to Equation (3).

Next, the background statistical fluctuation σ _B of the non-detected element is calculated from the measured intensity I _B1 and I _{B2 of} the non-detected element measured by the detecting means 9 by the equation (7) similarly to the detected element. To do.

Then, the detection limit LLD (= 3 kσ _B ) of the non-detectable element is calculated from the statistical fluctuation σ _{B of the} background of the non-detectable element and the calibration curve gradient k of the non-detectable element, using Equation (1).

As described above, according to the fluorescent X-ray analysis apparatus of this embodiment, the non-detection element, assuming the predetermined trace concentrations W _i so as not to affect the concentration of the composition that is detected element, the trace concentrations W _i Since the detection limit LLD is calculated based on the detection limit calculation composition added to the calculated composition, the detection limit LLD of the non-detection element can be accurately calculated for the individual samples 13 having different sizes and compositions.

Note that it is desirable to apply various conventionally used corrections to the measured intensity, which is the net intensity in the present invention. For example, if X-rays are absorbed by the film over the atmosphere and the sample is placed the sample, multiplied by the transmittance T _s of X-rays in the transmittance T _a and films X-rays in the atmosphere in the apparatus sensitivity coefficient K Thus, the corrected device sensitivity coefficient is used. In addition, the net intensity is obtained, but when the spectrum of other elements overlaps, and the overlap correction that removes them causes the analytical line intensity to become 0 and becomes a non-detectable element, the overlap intensity is included. The statistical fluctuation of the peak intensity is calculated and used as the statistical fluctuation of the background of the non-detected element.

  The fluorescent X-ray analysis apparatus of the above embodiment usually includes a computer, but a program for causing the computer to function as the calculation means, that is, a program for causing the computer to execute each of the above-described procedures is also included in the present invention. It is an embodiment.

1 is a schematic view showing a fluorescent X-ray analyzer according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray source 2 Primary X-ray 4 Secondary X-ray 9 Detection means 10 Calculation means 13 Sample

Claims (2)

An X-ray source for irradiating the sample with primary X-rays;
Detection means for measuring the intensity of secondary X-rays generated from the sample;
Based on the assumed composition, the theoretical intensity of secondary X-rays generated from each element in the sample is calculated, and the theoretical intensity and the measured intensity measured by the detecting means are converted into a theoretical intensity scale. In a fluorescent X-ray analysis apparatus provided with a computer as a calculation means for calculating the composition of the sample by sequentially correcting and correcting the assumed composition so as to match,
The calculating means is
For a non-detectable element not included in the calculated composition, a predetermined trace concentration is added to assume a detection limit calculation composition, and secondary X-rays generated from the non-detection element based on the detection limit calculation composition Calculate the theoretical strength of
From the theoretical strength of the non-detectable element and the device sensitivity coefficient obtained for conversion between the theoretical strength and the measured strength in advance, calculate the estimated measured strength of the non-detectable element,
From the estimated measurement intensity of the non-detectable element and the predetermined trace concentration, a calibration curve gradient of the non-detectable element is calculated,
From the measured intensity of the background of the non-detectable element measured by the detection means, calculate the statistical fluctuation of the background of the non-detectable element,
An X-ray fluorescence analyzer characterized in that a detection limit of a non-detectable element is calculated from a statistical fluctuation of a background of the non-detectable element and a calibration curve gradient of the non-detectable element.   The program for functioning the computer with which the fluorescent X-ray-analysis apparatus of Claim 1 is provided as the said calculation means.

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