in the positive mode, when the discharge current of corona discharge is 1-5 μa on the nebulized solvent, n gas molecules are excited and ionized, which produce n. the evaporated mobile phase of lc acts as the ionization gas and reactant ions. if water is the only solvent in the evaporated mobile phase, the excited nitrogen molecular ions n would react with ho molecules to produce water cluster ions h(ho). then, analyte molecules m are protonated by the water cluster ions. finally, the ionization products mh(ho) transfer out from the atmospheric-pressure ion source. declustering (removal of water molecules from the protonated analyte molecule) of mh(ho) takes place at the high vacuum of the mass analyzer. the analyte molecule ions detected by ms are [m+h]. the chemical reactions of ionization process are shown below.