Fig. 1

Workflow of a probe electrospray ionization-mass spectrometry (PESI-MS) and machine learning and b liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). In PESI-MS, a small amount of sample solution (9 μL) is placed onto the sample plate and directly analyzed without any further pretreatments. In this system, we use all spectral peaks to construct the database instead of annotating each spectral peak. In contrast, we separate the analytes by liquid chromatography in LC-ESI-MS, followed by annotation of each molecule. The data are further evaluated by statistical methods