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Abstract
Five novel ionic liquids based on quinoline and hexafluorophosphate, including one acidic ionic liquid and four neutral polyethylene glycol-based dicationic ionic liquids, were synthesized and used as extractants for the preconcentration of indigotin and indirubin from Indigowoad roots for the first time. The structures of the ionic liquids were characterized by spectral data. Their solubilities and viscosities were measured, and the latter were correlated with the Litovitz and Arrhenius equations. In the preconcentration of indigotin and indirubin, the type of ionic liquid, concentration of ionic liquid, solid-liquid ratio, temperature, and duration time on the preconcentration efficiency for indigotin and indirubin were investigated. Furthermore, high-performance liquid chromatography was used to determine indigotin and indirubin in Indigowoad roots. High selectivity and enhancement were obtained, and the method was validated for linearity, precision, repeatability, stability, recovery, and accuracy. The limits of detection were 0.0192 microgram per milliliter for indigotin and 0.0236 microgram per milliliter for indirubin, while the limits of quantification were 0.084 microgram per milliliter for indigotin and 0.040 microgram per milliliter for indirubin. This study provides a useful reference for the design and synthesis of task-specific ionic liquids, which may be applied for the separation of similar natural products.