Spectroscopic analysis method and analyzing system

Abstract: A plurality of elements in a sample (3) are specified as monitoring elements. Each time when exciting the sample (3), the light intensity of the line of the monitoring elements and the measured elements is detected and memorized. From the memorized data, the distribution for the light intensity of the line of each of the monitoring elements is determined. Based on the distribution, the preferred region for the light intensity of the line of each of the monitoring elements is defined. With reference to the memorized data, the light intensity of the line of the measured elements at each excitation in which the light intensity of the line of the monitoring elements is within the preferred region is integrated.

Description: BACKGROUND OF THE INVENTION The present invention relates to a spectroscopic analysis method and system. A spectroscopic analysis for a spark discharge is carried out such that spark discharge takes place betweeen a discharge electrode and a specimen, and the spark is subjected to spectrum analysis. The emission of the discharge is different each time the discharge is carried out. Therefore, the discharge is repeated several thousands of times in which the light amount of the line of each element is integrated. For quantitative analysis, a single element which is uniformly dispersed within the specimen at a predetermined amount is treated as an internal standard element. The light intensity of the line of the internal standard element is integrated. The integration of the light intensity of the line of a measured element at the time when the integration of the light amount of the line of the internal standard element reaches a predetermined amount is used as an analysis quantitative amount. However, the light amount of the spark discharge is irregular. At the discharge of which light amount is outside of the regular region, the light intensity of the line of the measured element is not always proportional with the light intensity of the line of the internal standard element. Thus, the simple integration of the measurement data of a great number cannot provide highly accurate analysis. Conventionally, to solve the above problem, each time a single discharge happens, as far as the light intenisity of the line of the internal standard element is in a certain region, the light intensity of the line of the internal standard element and the measured element is selectively integrated. However, the light intensity of the line of the internal standard element depends upon content by amount. Then, in this method, if the selective region of the light intensity of the line of the internal standard element is predetermined, the variation of the contents of the internal standard element is limited and the analysis is limited to analyzing a known specimen, disadvantageously. Although monitoring the single internal standard element may show the discharge proper, it is not sufficient to eliminate the effect of sparking to some defects such as pinholes and obstacles. EP-A-0 009 766 discloses an apparatus for emission spectrochemical analysis, in which a plurality of internal standards are utilized, each for a particular element to be determined. The ratios between the intensities of such pairs of lines are averaged and from this average the content of the element is read on a calibration curve. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide improved spectroscopic analysis method and analyzing system. Briefly discribed, in accordance with the present invention, in spectroscopic analysis, a plurality of elements in a sample are specified as monitoring elements. Each time when exciting the sample, the light intensity of the line of the monitoring elements and the measured elements is detected and memorized. From the memorized data, the distribution for the light intensity of the line of each of the monitoring elements is determined. Based on the distribution, the preferred region for the light intensity of the line of each of the monitoring elements is defined. With reference to the memorized data, the light intensity of the line of the measured elements at every excitation in which the light intensity of the line of the monitoring elements is within the preferred region is integrated. According to the spectroscopic analyzer and analyzing method, the elements uniformly contained other than the internal standard element are used as the monitoring elements. As far as the light intensity of the line of each of the plurality of monitoring elements is all within each predetermined level, the data of measured elements at this time are used as effective data. Uneffective data due to some defects in the specimen, poor discharge, optical dislocation and so forth can be effectively eliminated. To define the predetermined level, the analysis is repeated at a thousand to several thousands times in which the light intensity of the line of each of the plurality of monitoring elements and measured elements at each exciting is detected and memorized. Based on the memorized data, the distribution of the light intensity of the line of each of the plurality of monitoring elements is determined to set the predetermined level for each of the plurality of monitoring elements, easily and surely. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invnetion and wherein: FIG. 1 shows a block diagram of a analyzing system according to a preferred embodiment of the present invention; and FIG. 2 shows measument data given by the analyzing system of FIG. 1. FIG. 3 shows a block diagram of a analyzing system according to another preferred embodiemnt of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a block diagram of a analyzingy system according to the present invention. A spark chamber 1 is provided for sparking a specimen 3. The spark chamber 1 is full of argon gas. A spark circuit 2 is operated to generate sparking pulses. A facing electrode 4 is positioned in front of a specimen 3. A high voltage pulse is applied between the facing electrode 4 and the specimen 3 from the spark circuit 2 so that a spark discharge is enabled between the facing electrode and the specimen 3. A spectrophotometer 5 is provided having a vacuum inside. An entrance slit 6 is used to take out parallel radiation from the spark light generated between the facing electrode 4 and the specimen 3. The parallel radiation is directed to some predetermined direction. A diffraction grating 7 is provided for providing spectroscopic analysis. Exit slits 8 through 11 are positioned so that the spark on the spectroscopic image plane by the diffraction grating 7 is led to the position of the line of each of the monitoring elements. Thus, the spark passing through each of the exit slits 8 through 11 only is incident on photomultipliers 12 through 15. Single pulse integrators 16 through 19 are provided for integrating light intensity signal of the line detected by the photomultipliers 12 through 15 at the unit of each spark. A switch 20 is provided for subsequently forwarding the integration value (simple data), integrated by the integrators 16 through 19 to an analog/digital (A/D) converter 21. The A/D converter 21 is operated to transfer the received simple data to digital signals. A memory 22 is provided for storing the simple data subsequently and the other data. A microcomputer 23 is operated to control the respective elements and calculate measured value based on the data stored in the memory 22. The spark discharge between the specimen 3 and the facing electrode 4 is repeated at a thousand to several thousands times to measure the light intensity for each of the monitoring elements at each spark as shown in FIG. 2 (A) to FIG. 2(C). In FIG. 2, the length of the vertical bar at the same position - on the time axis for each of the monitoring elements indicates the light intensity of the line at a single spark. The given light intensity data of the line of each of the monitoring elements are subsequently stored into the memory 22. From the data stored in the memory 22, the average value and the dispersion value σ of the simple data of the monitoring elements (the internal standard elements, O, and H and so on) are determined. With reference to the dispersion conditions of the data, the effective region is then defined. For example, the effective region of the internal standard elements is set about ± 2σ as compared with the average. The effective region of the other monitoring elements is set lower than ± 2σ of the average. The reason why the excessive light intensity of the line for O and H is excluded is that the oxide and the hydroxide maybe made of these elements to thereby make the obstacles in the specimen and the deposits of the crystalline boundary. The reason why the light intensity of these elements are large is considered to scatter the spark to the obstacles and the crystalline boundary. As far as the spark is such that the simple data of each of the monitoring elements are all contained within the effective region of the monitoring elements thus determined, the light intensity of the line of the internal standard elements and the measured elements generated at this spark are treated as the effective simple data which is extracted from the data of the memory 22. That is, when any of the simple data of the monitoring elements is outside of the effective region (the sparks 4 ○, 5 ○, 6 ○ and in FIG. 2.), any measurement data at these sparks are not treated as effective measurement data. The extracted effective simple data of the measured elements and the internal standard elements are integrated. The integration of the measured elements at the time when the integration of the internal standard elements reaches a predetermined value is outputted as the measurement data. Otherwise, as shown in FIG. 2(E), the ratio of the effective simple data of the measured elements and the same data of the internal standard elements at the same spark is determined so that the average of the ratio is treated as the measured data. FIG. 3 shows another preferred embodiment in which the facing electrode 4 is replaced by the laser gun 30 and the spark circuit 2 is replaced by the laser gun driving circuit 31 so that the specimen 3 is excited by the laser beam. The other parts and the data processing operation are similar as the above embodiment. The suitable laser is N₂ laser beam which is featured by having short laser pulse and providing high output. When the N₂ laser beam is incident on a metal sample under the pressure lower than several torr, the white primary plasuma having the small diameter and the secondary plasuma which surrouds the white primary plasuma in a semispheric form are both generated. The emission of the secondary plasuma is used because the emission of the secondary plasuma can provide high analysis accuracy without the influence of the background. The emission of the laser beam is expanded over the entire surface of the specimen 3 with scanning. In the above embodiment using the spark discharge, the discharge position of the spark discharge is randomized so that if the discharge position is shifted to a single point, it is impossible to obtain the uniform analysis results over the entire surface of the specimen 3. However, in this preferred embodiment, the emission of the laser beam is carried out with scanning the entire surface of the specimen 3. Here, the average analysis results over the entire surface of the specimen 3 can be assured in this embodiment. As described above, the monitoring is carried out as to a plurality of elements so that the data only given at the spark when the data of all of the monitoring elements are considered proper are treated as effective. The abnormal data can be effectively eliminated to improve measurement accuracy. The predetermined level for excluding the abnormal value can be automatically set so that the predetermined level can be easily and surely set. The predetermined level is set according to the actual measurement. If iron which is the element of the stainless steel is treated as one of the internal standard element, the ratio of iron depends upon the type of stainless steel so that the average of the light intensity of the line of iron is also different from each other depending on the type of steel. Even if the type of stainless steel is uncertain, the predetermined level can be automatically and preferably set. This is true with the case where oxygen and hydrogen are selected as the monitoring elements, oxygen and hydrogen being contained in the nature with the different ingredient in the different specimen and the predetermined level is set for the monitoring elements. While only certain embodiments of the present invention have been described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the present invention as claimed.

Claims: A spectroscopic analyzing method comprising the following steps: defining a plurality of elements as monitoring elements in a specimen (3); exciting said specimen (3) at a number of times; detecting the light intensity of each emitted spectral line of the said monitoring elements and of elements to be measured each time said specimen (3) is excited; and storing the detected light intensity of each detected spectral line; characterized by: obtaining a distribution of the light intensity of the lines of said monitoring elements based on said stored data and for determining the effective region of the light intensity of the lines of said monitoring elements based on said distribution; and integrating the light intensity of the lines of said measured elements on each excitation only when the light intensity of each spectral line of said monitoring elements is within the effective region based on said stored data. The spectroscopic analyzing method as set forth in claim 1, wherein said determining step includes step for determining the average value and the dispersion value of the light intensity of the line of said monitoring elements. The spectroscopic analyzing method as set forth in claim 1, wherein said exciting step is carried out by discharge. The spectroscopic analyzing method as set forth in claim 1, wherein said exciting step is carried out by laser emission. A spectroscopic analyzing system comprising: exciting means (2,4; 30,31) for exciting a specimen (3); spectroscopic analyzing means (5) for spectroscopically analyzing the emission of said specimen (3); detection means (12-15) for detecting the light intensity of spectral lines of a plurality of predetermined monitoring elements, as well as spectral lines of elements to be measured of the spectroscopic analysis by said spectroscopic analyzing means (5) each time said specimen (3) is excited; and storing means (22) for storing the light intensity of each detected spectral line; characterized by: determining means (23) for obtaining a distribution of the light intensity of each spectral line of the said plurality of monitoring elements defined from the stored data by said storing means (22) and for determining an effective region of the light intensity of each spectral line of said monitoring elements based on said distribution; and integration means (16-19) integrating the light intensity of each line of said measured elements on each excitation, only when the light intensity of each line of said monitoring elements is within the effective region. The spectroscopic analyzing system as set forth in claim 5, wherein said determining means (23) obtains the distribution of the light intensity of the line of said plurality of monitoring elements by determining the average value and the dispersion value of the light intensity of the line of said monitoring elements. The spectroscopic analyzing system as set forth in claim 5, wherein said exciting means comprises a discharge means (1,4). The spectroscopic analyzing system as set forth in claim 5, wherein said exciting means comprises a laser emission means (30,31).

Inventors: FUKUI ISAO SHIMADZU CORPORATIO, MIYAMA TAKAO SHIMADZU CORPORAT, FUKUI, ISAO, SHIMADZU CORPORATION, MIYAMA, TAKAO, SHIMADZU CORPORATION
Applicants: SHIMADZU CORP, SHIMADZU CORPORATION
Application year: 1992
Main classification: G01J3
IPC codes: G01N21, G01J3