Organic-NaH2PO4-H2O aqueous biphasic system for extraction of paeonol from cortex moutan: Solvent selection and mechanism probing

Aqueous biphasic system (ABS) for extraction of active components attracted increasing attention due to advantages of high extraction efficiency and high product purity. However, solvent factors ruling extraction is still unclear. Four new ABSs with different organic solvent were designed for paeonol extraction, and the extraction conditions such as NaH 2 PO 4 concentration, organic solvent fraction, extraction period and temperature were examined with single factor method. The paeonol extraction yield, partition coefficient and paeonol purity with ABSs at optimized conditions were in the order as follows: ABS-THF-EA (33.6 ± 1.5 mg/g) ≈ABS-Ac-EA (33.0 ± 1.3 mg/g) > ABS-EtOH-EA (31.6 ± 1.6 mg/g)≈70 % ethanol (v/v) (31.2 ± 1.4 mg/g) > ABS-THF (28.8 ± 1.0 mg/g) > ABS-Ac (27.6 ± 1.2 mg/g) > ABS-EtOH (25.2 ± 1.2 mg/g), suggesting that replacing fraction of acetone/THF with ethyl acetate (EA) in ABSs could improve paeonol yield. Compositions and solvatochromic parameters for top phase of 12 ABSs were detected. Using LSER model, paeonol yield was strongly correlated to the dipolarity/dipolarizability (π*), hydrogen bond acidity (α) and hydrogen bond basicity (β) of top-phase medium in ABS ( r 2  = 0.982, n = 12); and partition coefficient was reasonably correlated to π*, α and β ( r 2  = 0.942, n = 12). Hydrogen-bond interaction and hydrophobicity interaction between paeonol and top-phase medium were crucial for efficient extraction. Solvatochromic parameters can offer guidance to solvent selection in extraction with ABS.