An electrospray ion source for magnetic sector mass spectrometers.

Electro spray mass spectra of carbonic anhydrase (MW ∼ 29000) and ovalbumin (MW ∼ 45000) were obtained on a double focusing magnetic secter mass spectrometer by using a single stage of mechanical pumping in the interface between atmospheric pressure and high vacuum. Full scan spectra of lysozyme were recorded on 15 fmoles consumed. In addition, accurate mass measurement was demonstrated for peptides and proteins, and resolution in excess of 10,000 (m /△m, 10% valley) was observed. These results clearly show that high performance magnetic sector mass spectrometers can be advantageously interfaced to an atmospheric pressure electrospray ion source.