In the work,we showed that the use of nanoemitters(tip dimension < 1 micron,typically~100 nm)could dramatically reduce the nonspecific metal adduction to peptide or protein ions as well as improve the matrix tolerance of electrospray ionization mass spectrometry(ESI-MS).The proton-enriched smaller initial droplets are supposed to have played a significant role in suppressing the formation of metal adduct ions in nanoemitters.