A novel preparative liquid chromatograph for repetitive enrichment and purification of low-abundance compounds

• A new preparative recycle HPLC system with a multifunctional trap was built up.
• The system was designed for separating a low abundant compound from a complex mixture.
• Absorption capability of the trap can be modified by online mobile phase adjusting.
• The system could work against the problems of volume overloading and solvent effect.
• The system could speed up the drying procedure of the final product.

A novel recycle preparative HPLC system was developed to repeatedly enrich and purify low-abundance compounds from complex samples. The recycle separation involves injecting a large volume of the sample through a trap column, releasing the absorbed sample for preparative HPLC separation, and then capturing the target component in the same trap column for the next separation. After several cycles, the final purified target compound absorbed in the trap column is eluted with a small volume of solvent. The capture and recycle procedure was realized by adjusting the strength of the mobile phase using an auxiliary pump and switching the two valves connecting the trap and preparative columns. Compared with standard HPLC or existing recycle chromatography, this system not only reduces the solvent side-effects and sample volume overloading during injection but also avoids peak–broadening and sensitivity loss during the recycle runs. Moreover, the final purified products can be easily concentrated. With the aid of this system, a 10% polyphenol in extracts from Saussurea involucrata cultured cells reached >95% purity with more than 95% recovery after three recycle purifications, and a 1% unstable epimer impurity in the raw material of the drug silybin reached >95% purity with 75% recovery after a six-cycle separation.