| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1205139 | Journal of Chromatography A | 2012 | 11 Pages |
In-line coupled comprehensive HILIC×RP systems should offer larger selectivity differences and better two-dimensional orthogonality than coupled RP×RP systems. However, this may not apply for all systems. The HILIC selectivity depends on the mix of selective polar and non-polar interactions with the functional groups, but also with the matrix of polar columns and depends on the sample type. We synthesized a new polar monolithic sulfobetaine polymethacrylate capillary column with excellent efficiency for low-molecular compounds. When used in the first, HILIC dimension coupled to core–shell or monolithic RP columns in the second dimension, this column provides much improved orthogonality for two-dimensional separations of phenolic and flavonoid compounds, in comparison to silica-bonded Diol, Polyethylene glycol or Zwitterionic columns. We investigated the performance of 11 short 5 cm and 3 cm columns for fast (1–2 min) gradient second-dimension separations. Band broadening or distortion may occur in directly coupled comprehensive HILIC×RP systems, due to strong solvent-strength differences between the mobile phases used in the first and in the second dimension. To suppress this effect, low fraction volumes were collected from a 0.5 mm I.D. capillary monolithic sulfobetaine column at the flow-rate of a few microliters per min, coupled in-line with various core–shell columns operated at the maximum flow-rate. This setup with simultaneous gradient elution in the HILIC and in the RP dimension provided successful separation of natural antioxidants.
► Various commercial core–shell columns are suitable for HILIC×RP 2D separations. ► A new efficient thermally stable capillary monolithic HILIC column was prepared. ► The capillary zwitterionic HILIC column is suitable for orthogonal 2D separations. ► Solvent strength incompatibility causes band broadening in HILIC×RP systems. ► Capillary columns in the first dimension and small fractions improve compatibility.
