Development of an on-line mixed-mode gel liquid chromatography × reversed phase liquid chromatography method for separation of water extract from Flos Carthami

•A novel on-line mixed-mode gel liquid chromatography × reversed phase liquid chromatography method was developed.•Size exclusion, reversed phase partition and adsorption separation mechanisms were involved in the first dimension.•A new interface solution was designed for the new 2D-LC system.•The new 2D-LC system exhibited better orthogonality (72.9%), better separation resolution and peak capacity.

A novel on-line comprehensive two-dimensional liquid chromatography (2D-LC) method by coupling mixed-mode gel liquid chromatography (MMG-LC) with reversed phase liquid chromatography (RPLC) was developed. A mixture of 17 reference compounds was used to study the separation mechanism. A crude water extract of Flos Carthami was applied to evaluate the performance of the novel 2D-LC system. In the first dimension, the extract was eluted with a gradient of water/methanol over a cross-linked dextran gel Sephadex LH-20 column. Meanwhile, the advantages of size exclusion, reversed phase partition and adsorption separation mechanism were exploited before further on-line reversed phase purification on the second dimension. This novel on-line mixed-mode Sephadex LH-20 × RPLC method provided higher peak resolution, sample processing ability (2.5 mg) and better orthogonality (72.9%) versus RPLC × RPLC and hydrophilic interaction liquid chromatography (HILIC) × RPLC. To the best of our knowledge, this is the first report of a mixed-mode Sephadex LH-20 × RPLC separation method with successful applications in on-line mode, which might be beneficial for harvesting targets from complicated medicinal plants.