Two-dimensional TLC with a sorbent gradient for the analysis of alfalfa root saponins

A mixture of saponin standards obtained from the roots of Medicago sativa ( Fabaceae) was chromatographed by two-dimensional TLC with a sorbent gradien t. In this variant of 2D-TLC (denoted as graft TLC) the first development w as performed on a TLC RP-18 plate and in the perpendicular direction on a T LC Silica gel plate. Additionally, the results obtained were compared with those acquired by 2D-TLC on the same monolayer stationary phase. The total saponin mixture consisting of 18 components could be separated into 17 indi vidual saponins with a sorbent gradient, but into only 15 saponins by conve ntional 2D-TLC. Moreover, when using sorbent gradient the spots were spread over a relatively larger surface area of the silica gel plate. The results obtained indicate that solid phase gradient TLC gave better separation of the soponin mixture investigated and was quite simple and easy to perform.