ESI (electrospray ionization) QTOF (tandem quadrupole/orthogonal-acceleration time of flight mass spectrometer (ESI-Q TOF MS/MS) is another type of mass spectrometer. In this type ionization is performed using electron beam. The peptide is fragmented before reaching the detector. Therefore this identification step is also know peptide fragment fingerprint (PFF).  The results that reflect the mass and ion charge ratio (m/z) are analyzed in silico.

For sample preperation, after peptide isolation and separation, we need to get peptide from protein mixture. For this purpose we can  perform in gel digestion by using protease enzyme such as trypsin or chymotrypsin. For the choice of trypsin our unit can be consulted.

ESI Q-TOF can be used to characterize post translational modifications.