XRD and Electron Microprobe Method in Mineral Drug Realgar Identification and Quality Evaluation

Realgar is a common mineral type of Chinese medicine in China. Due to the difference in crystal spatial structures, it can be divided into α realgar (AsS) and β realgar (As₄S₄). Realgar was oxidated to produce highly toxic substance arsenic (As₂O₃), whereas β realgar was more susceptible to oxidation due to its spatial structure. Therefore, ingredient identification and quality evaluation of mineral medicine realgar has an important significance. Common methods of arsenic and other elements in realgar (Atomic Absorption Spectrometry, Inductively Coupled Plasma Mass Spectrometry, High Performance Liquid Chromatography-Mass Spectrometry, etc.) is determined by measuring total arsenic, arsenic and other relevant valence elements to achieve the realgar identification and detection of harmful ingredients. The analysis process is complex, the consumption of reagent is large, and it could destroy the sample, but couldn't directly determine the structure of the mineral. In this paper, thin section identification, X-ray Diffraction and Electron Microprobe analysis were used to identify and quality evaluate with six kinds of medicinal realgar samples from representative producer in Sinan, Guizhou and Shimen, Hunan. Firstly, the main component and associated minerals of realgar samples were identified by thin section identification, further use of X-ray Powder Diffraction and Electron Microprobe analysis techniques to study main ingredient and semi-quantitative analysis of associated minerals. Secondly, the occurrence status of As, S and O in realgar was studied by using Electron Probe. The results show: No.1 mineral medicine from Sinan, Guizhou are composed by quartz (82.8%), calcite (9.5%) and dolomite (7.7%), with the No.2 mineral medicine are composed by α realgar (64.7%) and quartz (35.3%). The No.6 mineral medicine from Shimen, Hunan are composed by β realgar (86.5%) and tourmaline (13.5%), the No.3 and No.4 realgar are composed by α realgar single mineral, the No.5 mineral medicine are composed by β realgar single mineral. The As content in No.3, No.4 and No.5 samples is more than 70%, complied with Pharmacopoeia. Electron Microprobe analysis did not detect arsenic in the samples. Overall, realgars from Hunan have better quality. Studies have shown that, according to correspondence between diffraction patterns and crystal structure, exclusive characteristics of different samples of mineral drugs were found by X-ray Powder Diffraction method. Furthermore, drugs for multi-component mineral samples, as long as the mixing of the components is constant, its diffraction pattern is relatively stable, which is a fingerprint characteristics. Occurrence status study of As, O and other elements can effectively evaluate the quality of realgar by Electron Microprobe. Combined with X-ray Diffraction and Electron Microprobe techniques for the identification of realgar mineral drugs is an extremely effective and feasible approach, compared with the traditional method, it is more quickly and economically.