An integrated analytical workflow for characterizing insoluble matter in traditional Chinese medicine injections: Danshen and Guanxinning injections as case studies.

Insoluble particulate matter (IPM) in traditional Chinese medicine (TCM) injections is compositionally heterogeneous and difficult to characterize using a single analytical technique. In this exploratory product-level study, particle-prone Danshen Injection (DI) and Guanxinning Injection (GXNI) samples were pooled separately by product and fractionated by refrigerated centrifugation. Dimethyl sulfoxide/methanol (DMSO/MeOH) extracts of washed precipitates and corresponding supernatants were profiled by LC-HRMS; the DMSO-d6-soluble fraction of washed precipitates was examined by ¹H NMR, HSQC and HMBC, and dried solids by FTIR; and representative insoluble materials from both products were characterized by SEM-EDS. LC-HRMS yielded 182 candidate annotations, of which 56 were confirmed with reference standards. Of the candidates detected in precipitate extracts, 81.5% (DI) and 82.9% (GXNI) were also detected in the corresponding supernatants, supporting chemical continuity between the solvent-extractable precipitate-associated fraction and the soluble formulation matrix. Selected lower-polarity or esterified constituents showed higher relative responses in precipitate extracts, including dihydrotanshinone I, tanshinone I, danshenxinkun A, miltirone, senkyunolide C and phenethyl ferulate. NMR showed aromatic/olefinic proton environments and proton-carbon correlations, while FTIR showed O-H, carbonyl-related, and C-O/C-O-C absorption features. SEM-EDS revealed C/O/N-rich organic-like materials in both products; DI additionally showed Na/Cl-rich crystals, Si/Al/O-rich dense particles, Fe-containing particles and C/O/N-rich fiber-like particles, whereas a Si-rich particle was observed in GXNI. Collectively, the findings support a composite particulate system in which a formulation-related extractable organic fraction coexists with salt-related, inorganic and fiber-like particle categories. The workflow links fraction-associated organic profiles with particle morphology and elemental composition to guide further investigation of insoluble matter in these formulations.