Strontium isotope ratio in medicinal plant as a geochemical tracer: Application to the geographic provenance of the relics of Magnoliae Officinalis Cortex in imperial pharmacy of Qing Dynasty

Because producing area is one of important parameters affecting the quality of industrial products, geographic discrimination of industrial products becomes important. The use of strontium isotope ratio ( 87 Sr/ 86 Sr), a key geochemical tracer, to establish geographic discrimination model is in the ascendant. In the present work, a geographic discrimination model based on 87 Sr/ 86 Sr for Magnoliae Officinalis Cortex (MOC), a traditional Chinese medicine (TCM), was established and was applied to trace the geographic origin of MOC relic in imperial pharmacy of Qing Dynasty for the first time. The value of 87 Sr/ 86 Sr was measured using a multi-collector inductively coupled plasma mass spectrometer, by which the variabilities of 87 Sr/ 86 Sr were compared among different types of plants, different parts of the same plant, and different depths of soil to offer a reliable methodology. A reference map of 87 Sr/ 86 Sr was drawn containing 143 MOC samples data collected from 23 areas by empirical Bayesian kriging. As a result, regional difference on 87 Sr/ 86 Sr was observed from both of plant and soil samples, and no significant differences were observed for different types of plants or for different parts of the same plant in same geographic area. The 87 Sr/ 86 Sr of MOC reflected well to the bioavailable 87 Sr/ 86 Sr of soils at depths of 0–10 cm and 20–30 cm. The reference map of 87 Sr/ 86 Sr based on MOC data was successfully established with good predictive ability, from which the MOC relic was suggested to come from Hubei and Sichuan, and the result was further supported by the evidence from local chronicles in Qing Dynasty. This study extends the application of 87 Sr/ 86 Sr for provenance of TCM relics, providing direct evidence for the geographic origin of Dao-di herbs.