I have expressed a human glycoprotein in plant ER through a signal sequence and it also contains ER retention signal at the C-terminus. Thus, if this protein contains an N-glycan moiety, it should be the high mannose type. To confirm the high mannose type glycan, I want to do MALDI-TOF mass spectrometry after purification of this protein. So, What is the minimum concentration of glycoproteins required for this analysis? Any suggestions would be greatly help!