“…The branch of ambient ionization methods has been proposed to analyze various biomolecules in complex matrices, such as saliva, blood, or even biopsy samples without elaborate pretreatment [ 3 , 7 , 10 ], including desorption electrospray ionization (DESI) [ 11 , 12 ], direct analysis in real time (DART) [ 13 ], low-temperature plasma (LTP) [ 14 ], desorption atmospheric pressure chemical ionization (DAPCI) [ 15 ], a variety of touch spray methods [ 16 , 17 ], and one of the most prominent ambient ionization mass spectrometry methods, paper spray (PS) [ 18 , 19 , 20 , 21 ]. Multiple studies have been devoted to investigating the capabilities of PS in performing targeted analysis of substances, such as illicit drugs, therapeutic drugs, metabolites, lipids, and proteins [ 18 , 19 , 21 ].…”