Online supercritical fluid extraction – supercritical fluid chromatography – diode-array detection: an interesting approach for investigation of milk thistle (Silybum marianum) preparations

Online supercritical fluid extraction – supercritical fluid chromatography – diode-array detection (SFE-SFC-DAD) is a new and innovative analytical tool that allows fully automated sample preparation followed by chromatographic separation in a single flow path. Among its ecofriendly character, rapid extraction and analysis, as well as reduced artificial operation errors make it to an interesting approach for natural product analysis [1], [2]. The purpose of this study was to investigate its suitability for rapid quality control of commercially available milk thistle preparations. These preparations are widely used due to hepatoprotective abilities credited to the contained silymarin, an isomeric mixture of flavolignans [3]. During method development, a multitude of parameters associated with the online coupling of extraction and analysis had to be investigated. A chiral amylose carbamate column was identified as ideal stationary phase, as it traps the analytes at the head of the column until the end of the extraction and subsequently enables rapid chromatographic separation of the selected marker compounds (silydianin, silychristin, silybin A, silybin B, isosilybin A, isosilybin B). Suited extraction parameters had to be conducted based on their extraction efficiency and their influence on the chromatographic resolution. Best results were obtained by using 20% ethanol as modifier for 15 min, at a temperature of 40°C and a pressure of 150 bar. Finally, the developed online SFE-SFC-DAD method had been applied to the qualitative analysis of different milk thistle preparations. With a total runtime of 30 min, including extraction as well as analysis, the assay provides an interesting approach for further investigations.

• References

• 1 Sakai M, Hayakawa Y, Funada Y. et al. Development of a split-flow system for high precision variable sample introduction in supercritical fluid chromatography. J Chromatogr A 2017; 1515: 218-231
• 2 Wicker AP, Jr DD C, Tanaka K. et al. On-line supercritical fluid extraction—Supercritical fluid chromatography-mass spectrometry of polycyclic aromatic hydrocarbons in soil. J Chromatogr B 2018; 1086: 82-88
• 3 Morazzoni P, Bombardelli E. Silybum marianum (Carduus marianus). Fitoterapia 1995; 66: 3-42