Direct coupling of thin-layer chromatography-bioautography with electrostatic field induced spray ionization-mass spectrometry for separation and identification of lipase inhibitors in lotus leaves

•A surface treatment method of normal-phase thin layer chromatography (TLC) plates with dimethyl silicone oil coating.•Direct coupling of normal-phase TLC to electrostatic field induced spray ionization (EFISI)-MS analysis.•Rapid and direct identification of lipase-inhibitory alkaloids in Nelumbo nucifera leaves by the TLC-EFISI-MS method.

In situ profiling compounds in complex matrices is important technology to develop in analytic chemistry. The aim of this study is to develop a direct coupling method of thin layer chromatography (TLC) to mass spectrometry (MS) via electrostatic field induced spray ionization (EFISI). We proposed a surface treatment method of normal-phase thin layer chromatography (TLC) plates with dimethyl silicone oil coating which successfully allowed TLC to couple to MS via EFISI. Different parameters affecting the ionization efficiency were investigated and optimized, including silicone oil concentrations, air-drying times, applied voltages, and TLC plate types. This optimized TLC-EFISI-MS method was successfully applied to examine lipase inhibitory components present in lotus leaves. Six active alkaloids including three aporphines and three benzylisoquinolines were profiled with their MSn (n = 4) data, or with a comparison with reference substances. This is the first report on the coupling EFISI-MS to TLC or TLC bioautography for in situ identification of active natural products.

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