Zeptomole-sensitivity electrospray ionization - Fourier transform ion cyclotron resonance mass spectrometry of proteins

Methods are being developed for ultrasensitive protein characterization bas ed upon electrospray ionization (ESI) with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The sensitivity of a FTICR mass spe ctrometer equipped with an ESI source depends on the overall ion transmissi on, which combines the probability of ionization, transmission efficiency, and ion trapping in the FTICR cell. Our developments implemented in a 3.5 t esla FTICR mass spectrometer include introduction and optimization of a new ly designed electrodynamic ion funnel in the ESI interface, improving the i on beam characteristics in a quadrupole-electrostatic ion guide interface, and modification of the electrostatic ion guide. These developments provide a detection limit of approximately 30 zmol (similar to 18 000 molecules) f or proteins with molecular weights ranging from 8 to 20 kDa.