Post translation modification site analysis

Protein expression will not only be determined by physiological changes of the cell, post-translational modification (PTM) is also a critical factor. The traditional method of identifying PTM site of a protein is done by antibodies, which will be affected by the specificity of an antibody, and also by a chance that there is no antibody that can bind to the specific PTM site. 
Using mass spectrometry method can not only analyze and identify all the possible PTM site of a protein but also it is much more direct than identifying through an antibody, which can be more convincing.