title: Composition of Indigo naturalis.
abstract: A proposal for a European Pharmacopoeia monograph concerning Indigo naturalis has recently been published, whereby the indigo (1) and indirubin (2) content should be determined by HPLC-UV. This method was tested, but problems were seen with the dosage of indigo due to poor solubility. A quantitative assay for indigo based on (1)H-NMR was developed as an alternative. The HPLC and qNMR assays were compared with eight Indigo naturalis samples. The HPLC assay consistently gave much lower indigo concentrations because solubility was the limiting factor in sample preparation. In one sample, sucrose was identified by (1)H-NMR as an organic additive. Simple wet chemistry assays for undeclared additives such as sugars and starch were tested with artificially spiked Indigo naturalis samples to establish their limits of detection, and sulfate ash determinations were carried out in view of a better assessment of Indigo naturalis in a future European monograph.
authors.affiliation: Institute of Pharmaceutical Biology, University of Basel, Basel, Switzerland.
authors.forename: Inken
authors.initials: I
authors.lastname: Plitzko
authors.forename: Tobias
authors.initials: T
authors.lastname: Mohn
authors.forename: Natalie
authors.initials: N
authors.lastname: Sedlacek
authors.forename: Matthias
authors.initials: M
authors.lastname: Hamburger
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods; D007203:Indigo Carmine; D029883:Indigofera / Q000737:chemistry*; D007211:Indoles / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D012015:Reference Standards
chemical_list: D007211:Indoles; D007203:Indigo Carmine; C027185:indirubin