Comparison of analytical and semi-preparative columns for high-performance liquid chromatography–solid-phase extraction–nuclear magnetic resonance

The application of analytical and semi-preparative columns in reversed-phase liquid chromatography–solid-phase extraction–nuclear magnetic resonance (HPLC-SPE-NMR) was compared. The work was aiming at separating a higher sample amount in a single run and in this way to reduce the necessary NMR measurement time of separated compounds. Several parameters for compound separation and trapping procedures were optimised: flow rate of HPLC and make-up water pumps, choice of stationary phase cartridges and drying time. The separation and loadability of nine model compounds on analytical and semi-preparative columns was determined, as well as the focussing capacity of SH-type SPE cartridges. It was found that a semi-preparative column—or multiple peak trapping on analytical columns—gave better results than a standard 4.6 mm analytical column for non-polar compounds (e.g. flavonoid aglycones, sesquiterpene lactones, non-polar terpenes, log P > 2), but for polar compounds (log P < −2) did not offer any advantage over an analytical column, or was even disadvantageous. For intermediately polar compounds (−2 < log P < 2) this has to be investigated per compound.