Suitable analysis of α-amino acids by a direct combination of thin-layer chromatography and matrix-assisted laser desorption/ionization mass spectrometry in conjunction with post-chromatographic fixed-charge derivatization.

• Post-chromatographic fixed-charge derivatization was used to record MALDI mass spectra of amino acids from TLC plates. • Chemical labeling is based on reaction of α-amino acids with tris(2,6-dimethoxyphenyl)methenium salt. • TLC/MALDI mass spectra of derivatives contain intense peaks of their decarboxylated cationic parts. On-spot fixed-charge derivatization has been suggested for the modification of α-amino acids for their analysis by thin layer chromatography/matrix-assisted laser desorption ionization (TLC/MALDI) mass spectrometry. The approach was based on post-chromatographic treatment of separated analytes by tris(2,6-dimethoxyphenyl)methenium salt and triethylamine. The reaction proceeded smoothly in mild conditions and gave rise to pink-red colored derivatives, containing permanent positive charge. Their MALDI mass spectra, recorded directly from TLC plates, revealed intense peaks corresponding to decarboxylated cationic parts. All derivatives are characterized by high ionization efficiency, which indicates the high sensitivity of the developed method for analyzing amino acids. Applicability of the method to analysis of amino acids was demonstrated on artificial mixtures and dietary supplement.