Comprehensive thin-layer chromatography mass spectrometry of flavanols from Juniperus communis L. and Punica granatum L.

• Use of the TLC–MS interface for the analysis of flavanols was explored.
• Performance with different HPTLC sorbents and developing solvents was evaluated.
• A new TLC × MS procedure was developed for sampling entire TLC chromatograms.
• Catechin and proanthocyanidins were detected for the first time in juniper seeds.

The coupling of thin-layer chromatography with mass spectrometry (TLC–MS) for the analysis of monomeric flavanols and proanthocyanidins in samples presented as complex matrices has been studied. The elution conditions for TLC–MS were optimised and full scans were compared with selected reaction monitoring for the MS detection of compounds. The performance of silica gel and cellulose plates with different developing solvents in TLC–MS was assessed. Cellulose plates provided superior sensitivity while ionisation suppression was encountered with silica plates. The use of a HILIC guard column beyond the elution head was found to facilitate detection of monomer compounds on silica plates. A new comprehensive TLC × MS procedure for screening flavanols in the entire chromatogram was developed as an alternative to the use of 4-dimethylaminocinnamaldehyde to determine the locations of compounds on the plate. This new procedure was applied to detect flavanols in the peel of Punica granatum L. fruits and in seeds of Juniperus communis L., in which flavanols and proanthocyanidin dimers and trimers were detected for the first time.