Raman mapping as a quantitative tool for the visual analysis of Chinese mineral medicine

To facilitate the reliable analysis of the inorganic ingredients in Chinese mineral medicine, a validated Raman mapping strategy for assaying aluminum potassium sulfate dodecahydrate (KAl(SO₄)₂·12H₂O) in alumen was reported. In this strategy, the internal standard quantitation and simple pellet methods were introduced to minimize the interference from undesirable backgrounds. The impact of the physical properties (including particle size and compactness) of the as-prepared tablets on Raman signals was also systematically evaluated. Compared with the dramatic signal fluctuation (RSD > 25%) observed in random single-point Raman measurement, the Raman mapping measurement exhibited significantly higher repeatability (RSD < 5%). The entire process can be completed within 30 min. Meanwhile, the spatial visualization distribution of the multiple compounds from the as-prepared tablets was achieved by assigning different colors using Raman mapping with the MATLAB imaging algorithms. Compared with the titration method commonly used in mineral medicine quantification, the validated Raman mapping strategy for non-destructively analyzing KAl(SO₄)₂·12H₂O greatly simplified the complicated operating steps and improved the reproducibility of experiment results. This could provide a new window for inorganic sample analysis, particularly in the quantification of mineral medicine.