Problem: You have expressed a human protein heterologously in Escherichia coli BL21[DE3] and purified the protein using Ni-NTA resin. She wants to know if she has expressed the correct protein and whether it is post-translationally modified. She runs the protein on an SDS-PAGE gel and observes multiple bands, but one dominant band at the approximate correct size. Describe how you would use liquid chromatography mass spectrometry to analyze whether she has expressed the correct protein. Include sample preparation, which kind of liquid chromatography and which mass spectrometer, would be best.