The loss of dopant radical cations under direct APPI mode induced the signal decrease of the analyte (Fig. 4 and Fig. 5). However, for analyte molecules with ionization Splitomicin over that of dopant and less than the energy of photon, the addition of dopant might reduce the reaction chances between the analyte molecules and photons, leading to a reduction of the number of analyte ions. Multiple chromatographic peaks of C12H10O5 shown in Fig.