## 5 Conclusions  
Thus, the developed algorithm for the accurate accounting of plasma background radiation in the analytical-lines area enables:  
* The significant reduction in RMS deviation while determining low impurity content in samples due to the optimal slope of the calibration curve in the area of low impurity concentrations;
* The scaling down of the detection limit of the sample impure element, in case plasma background radiation inaccuracy exceeds 3\(\sigma\) of the background (where \(\sigma\) is the RMS deviation of the plasma background radiation from its average statistical value);  
Figure 8: The same as shown in Figure 7, only to determine Ti in low- and medium-alloyed steels.  
Figure 7: Calibration curves to determine phosphorus concentration in low- and medium-alloyed steels on SPAS-05 emission spectrometer, serial number \(N18\); 1—with accurate accounting for plasma background radiation; 2—without accurate accounting for plasma background radiation; 3—nameplate concentration values \(P\) in a SS.  
* The use, in commercial factory device calibration, of a maximum of two standard samples, rather than several dozens of them, to find linear-conversion parameters of the analytical-line intensity of a certain element by the recalibration algorithm.  
We have clarified the conditions under which it is possible to apply conventional recalibration techniques (i.e., how the changes in a spectrometer parameters influence calibration curves during its continuous operation). Namely, this algorithm can be applied only in the case when the conditions for analytical-line intensity formation in plasma do not change while the device is in use, i.e., the spectrum-excitation-source parameters, inter-electrode distance, and in the case of utilizing specific plasma-forming gases, their purity, etc., stay unchanged. The algorithm is also applicable if there is a change in the transmission coefficient of the spectrometer and the parameters of analytical-line-intensity conversion into an electric signal.  
Thus, special attention should be paid to the stability of the spectrum-excitation-source parameters when developing emission spectrometers.  
It is defined that the linear relationship between the intensities measured by an emission-spectrometer recording system, when their parameters change, can only be implemented if the coefficients of transmission and intensity conversion into an electric signal by the recording system are independent of the analytical-line intensity. Otherwise, it is necessary to raise the degree of the polynomial relationship between these intensities, and therefore, to increase the number of standard samples required for recalibration.  
Conceptualization, V.S.S. and A.S.M.; methodology, A.N.P., V.S. and A.S.M.; software, A.N.P. and V.S.S.; validation, A.N.P. and V.S.S.; formal analysis, A.N.P. and V.S.S.; investigation, A.N.P.; resources, A.N.P. and V.S.S.; data curation, A.N.P. and V.S.S.; writing--original draft preparation, A.N.P.; writing--review and editing, A.N.P. and V.S.S; visualization, A.N.P.; supervision, V.S.S. and A.S.M.; project administration, A.N.P.; funding acquisition, A.N.P. All authors have read and agreed to the published version of the manuscript.  
This research was carried out by the Russian Science Foundation (RSF), the grant No. 21-19-00139.  
Not applicable.  
All the data used is available in the article.  
The authors declare no conflict of interest.