Abstract：The fitting error of standard curve in arc emission spectrometry is relatively large, which is the main factor affecting the uncertainty of measurement results. Optimizing curve fitting and reducing the fitting error of standard curve are important methods to improve the reliability of measurement results. The common polynomial standard curve in arc emission spectrometry uses the principle of minimum sum of squares of absolute error to fit. The fitting error of low content point is usually large, while the fitting error of high content point is usually small. Another common logarithmic standard curve uses the principle of minimum sum of squares of relative error to fit. The fitting error of low content point is usually small, while the fitting error of high content point is usually large. According to the characteristics of two standard curves, the method of subsection measurement was adopted. The intermediate standard point content was set as the conversion value. The logarithmic standard curve was used for determination for the condition equal to or less than the conversion value, while the polynomial standard curve was used for the condition higher than the conversion value. The fitting error of the standard curve could be reduced in the whole curve range, thus improving the reliability of measurement results. The contents of silver in 50 national primary certified reference materials of geochemical sample were determined by arc emission spectrometry with segmented curves. According to the determination requirements in industry standard of geology and mineral resources (DZ/T 0258-2014), the qualification rate of accuracy of measurement results increased from 90% (polynomial standard curve method) and 92% (logarithmic standard curve method) to 98%. Meanwhile, the qualification rate of precision was also improved from 98% to 100%.
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