• • Indigo and indirubin content in commercial Indigo Naturalis varies dramatically: indigo from 0 to 9.00% and indirubin from 0 to 0.60% (HPLC, ref 132), while another study reports indigo at 1.18–3.47% and indirubin at 0.09–0.26% (ref 131). This 9-fold variability in indigo content directly compromises batch-to-batch clinical efficacy and safety, necessitating stringent quality control.
• • Inorganic fraction dominates: CaCO3 ranges from 23.65% to 38.47% (ICP-OES) and 68.51% to 71.50% (titration), with SiO2 at 7.78–11.09% (gravimetric) and total ash 60.0–88.0%. This 90% inorganic matrix is largely ignored in current quality standards, yet it may influence drug stability, bioavailability, and toxicity.
• • Trace bioactive compounds are present at nanomolar to micromolar levels: indole at 22 nmol/g, indole-3-carbaldehyde at 1.4 nmol/g, tryptanthrin at 5.0 nmol/g, and indigo at 9569 nmol/g (LC-MS, ref 26). These minor constituents may contribute to pharmacological effects but are not routinely quantified, representing a gap in holistic quality assessment.
• • Processing yield is critically low: from 100 kg of Baphicacanthus cusia stems and leaves, only 7–8 kg of crude indigo is obtained, and merely 0.1 kg of indigo flower (靛花). This 1.25% yield of indigo flower versus 7–8% crude indigo forces industry to use crude indigo, which lacks the traditional purity and may contain higher impurities, driving adverse reactions.