Quantitative analysis of flavanones and chalcones from willow bark

Willow bark extracts are used for the treatment of fever, pain and inflammation. Recent clinical and pharmacological research revealed that not only the salicylic alcohol derivatives, but also the polyphenols significantly contribute to these effects. Quantitative analysis of the European Pharmacopoeia still focuses on the determination of the salicylic alcohol derivatives. The objective of the present study was the development of an effective quantification method for the determination of as many flavanone and chalcone glycosides as possible in Salix purpurea and other Salix species as well as commercial preparations thereof. As Salix species contain a diverse spectrum of the glycosidated flavanones naringenin, eriodictyol, and the chalcone chalconaringenin, a subsequent acidic and enzymatic hydrolysis was developed to yield naringenin and eriodictyol as aglycones, which were quantified by HPLC. The 5-O-glucosides were cleaved with 11.5% TFA before subsequent hydrolysis of the 7-O-glucosides with an almond β-glucosidase at pH 6-7. The method was validated with regard to LOD, LOQ, intraday and interday precision, accuracy, stability, recovery, time of hydrolysis, robustness and applicability to extracts. All 5-O- and 7-O-glucosides of naringenin, eriodictyol and chalconaringenin were completely hydrolysed and converted to naringenin and eriodictyol. The LOD of the HPLC method was 0.77 μM of naringenin and 0.45 μM of eriodictyol. The LOQ was 2.34 μM of naringenin and 1.35 μM for eriodictyol. The method is robust with regard to sample weight, but susceptible concerning enzyme deterioration. The developed method is applicable to the determination of flavanone and chalcone glycosides in willow bark and corresponding preparations.