Objective  To determine the contents of various inorganic elements in raw and processed Rubia cordifolia, analyze their differential changes, and distinguish them accurately using multivariate statistical analysis.

Methods  This method utilizes microwave digestion technology for efficient and uniform pretreatment of experimental samples. The digested sample solutions were then subjected to simultaneous quantitative analysis of 37 inorganic elements in both raw and processed Rubia cordifolia using inductively coupled plasma mass spectrometry (ICP-MS). Statistical analysis was subsequently performed on the obtained data. Additionally, hierarchical cluster analysis (HCA), principal component analysis (PCA), and orthogonal partial least squares-discriminant analysis (OPLS-DA) were employed to conduct clustering and differential analysis of all samples, aiming to elucidate the potential relationships among raw Rubia cordifolia, its processed products, and the 37 inorganic elements.

Results  A total of 37 inorganic elements were analyzed, with 3 remaining undetected. Paired t-test revealed that 58.8% of the elements exhibited statistically significant differences in content. HCA enabled clear discrimination between the two sample groups, whereas the discriminative power of PCA was limited. The OPLS-DA model demonstrated robust fitting and predictive performance, leading to the final identification of 16 differential inorganic elements.

Conclusion  This method can facilitate the accurate differentiation between raw and processed Rubia cordifolia, providing new research ideas and approaches for studying the differences in inorganic element contents between raw and processed Chinese herbal medicines.

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