Electrospray ionization mass spectrometry is a special soft ionization technology that can generate gas phase ions with multiple charges more gently, reducing the mass-to-charge ratio range of the molecules to be measured. The product ions of multi-charged precursor ions can also provide more structural information than the product ions of single-charged precursor ions. Electrospray ionization mass spectrometry not only can obtain accurate molecular weight of compounds, but also can be used for quantitative and qualitative analysis of trace or trace biologically active molecules.