Effect of internal standard sample selection on the accuracy of the calibration curve

Abstract

In this study, the internal standard method, a type of X-ray diffraction method, was used for the quantitative analysis of rust. Internal standard samples were selected and calibration curves were prepared with standard samples (iron hydroxides α, γ, and ferric tetroxide). In addition to the conventionally used calcium fluoride and zinc oxide, the chemically stable magnesium oxide was employed as the internal standard sample. Standard deviation, coefficient of determination, and residual plots were used to evaluate the calibration curves. As a result, it was confirmed that the variation tended to be larger in the higher concentration range, and the analysis of the coefficient of determination and residual plots indicated that the calibration curve was more accurate when approximated by a curve. The calibration curve using zinc oxide (ZnO) was the most accurate, and the quantitative analysis using a simulated rust sample showed the smallest error of approximately 1%.