The LTQ XL has an MSn performance with multiple dissociation techniques (PQD, ETD, and CID) which is powerful tool to generate more structural information in protein and peptide analysis. The unique property of electron transfer dissociation (ETD) option provides new peptide sequence structure information not available from conventional methods. ETD produces c- and z-type peptide fragment ions, complementing the y- and b-type fragments generated during traditional CID of peptides by ion trap analysis. This additional information allows for more complete characterization of peptides and proteins than is possible with CID alone. With ETD technology, post-translational modifications can be identified with a great confidence. Two-dimensional liquid chromatography (2D-LC) from DIONEX is coupled with this instrument.