NANO ELECTROSPRAY COMBINED WITH A QUADRUPOLE ION-TRAP FOR THE ANALYSIS OF PEPTIDES AND PROTEIN DIGESTS

A nano electrospray (NanoES)/ion trap combination was developed to tak e advantage of the long spraying time of the NanoES source (Wilm, M. S .; Mann, M. Int. J. Mass Spectrom. Ion Processes 1994, 136, 167-180) f or extensive experiments on the ion trap. The low flow rate associated with the NanoES allows for optimization of experimental conditions an d data acquisition for more than 30 min with 1 mu L of solution. Thus, even time-consuming experiments, such as multiple fragmentation steps or the sequencing of many components in a mixture, can be performed w ith very small volumes of sample. Stored waveform inverse Fourier tran sformation (SWIFT) signals were used during the injection period to ac cumulate ions of low intensity and to improve the dynamic range of the quadrupole ion trap. To sequence peptides, a combination of nozzle-sk immer fragmentation, SWIFT accumulation of a single fragment to high i ntensity, and a second fragmentation step was employed to obtain compl ete sequence information. Unseparated peptide mixtures were infused an d weak portions of the spectrum were enhanced by using the SWIFT metho d, followed by fragmentation of various accumulated peptide ions.