In the process of using the direct-reading spectrometer
, in addition to the elements of the sample itself, the vacuum, electronic circuits, ambient temperature, ambient humidity, constant temperature of the optical room, pollution of the optical path, and misalignment of the slit will cause the working curve to drift. As a result, measurement errors increase. In addition, the lens is contaminated to form a coating, which causes the electrode to be sharp during the excitation process, which increases the background of the curve display, and changes in argon flow, pressure, and purity can also cause the curve to drift. In particular, the spectral lines of the C, P, and S elements are located in the far ultraviolet region, and the changes are particularly sensitive, so it is very important to correct the working curve. Selecting a set of high and low standards and performing data calibration before analysis and calculation will save a lot of calibration time and simplify operation procedures.
Normally samples need to be standardized before analysis. The calculation of standardized data is performed automatically by a computer. Selecting a standardized set of samples is difficult, including high and low levels of all elements to be analyzed. The direct-reading spectrometer standardized sample must excite the standardized sample while making the elemental working curve to ensure that the curve is not shifted. In the 1-point standardization, only high or low content standards are sufficient. If the sample can cover a wide range of content, and high accuracy is required at low content, 2-point standardization is required. At this time, two kinds of standard samples are needed, one for high standard and one for low standard. Or each standard can contain some high-concentration elements and other low-concentration elements, as long as they can include all elements. The high and low concentration values are not necessarily exactly at the highest or lowest end of the calibration range. But they should be close to the highest and lowest ends of the range, and there should be enough difference between them. The high and low standards are used to correct the deviation of the measured value from the working curve due to the change of the instrument
over time, and then recalibrate to correct the drift of the instrument in the medium and long term.
In the spectral analysis, in order to directly use the original working curve, it is necessary to periodically recalibrate the original analysis curve with recalibration samples. When two-point recalibration is used, the element content of the two recalibration samples used should be sufficiently different, and ensured at the high and low ends of the elemental analysis range. In fact, the low-end recalibration samples often use "pure" matrix samples, which means that they actually contain only this alloy matrix, and the content of other elements should be zero, trace, or very small. Make a low. Theoretically, such two samples are sufficient to restandardize the instrument. However, in actual work, in order to ensure the accuracy of the instrument, it is generally impossible to cover all high-end and low-end of all elements with only two recalibration samples. Therefore, a larger number of samples are often required for recalibration. On the other hand, the recalibration procedure can be used for more than one alloy, and in principle it can be used for a group of alloys. At this time, multi-point recalibration is more convenient and effective.