Matrix-assisted laser desorption/ionization (MALDI) from the surface of nanosized multimolecular structures based on lanthanum stearate monolayers (FLa) has been studied. The presence of FLa on the surface of MALDI target was confirmed experimentally by laser desorption of lanthanum-containing organic ions. MALDI target functionalization with FLa is shown to significantly increase the yield of target peptide ions, with the optimum being achieved at a film thickness of about 6 monolayers. An approach is proposed in a "lab-on-a-plate" format, which allows specific extraction of peptides modified with chlorine-containing compounds and includes the following steps: functionalization of the target surface, metal affinity extraction, matrix deposition and MALDI mass spectrometric analysis. Keywords: mass spectrometry, matrix assisted laser desorption/ionization (MALDI), surface, Langmuir monolayers, metal affinity chromatography.