This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': 'All of the following are techniques of protein purification and separation, EXCEPT: \nSelect and explain. \nA. Chromatography, B. Centrifugation, C. Electrophoresis, D. Densitometry', 'role': 'user'}, {'content': "Answer: D \nExplanation: Purified proteins can be obtained by several methods: gel-filtration chromatography, ion-exchange chromatography, immunoaffinity chromatography, immunoprecipitation, and salt precipitation. New methods are, micropreparative electrophoresis, and centrifugation. Ref: Harper's Illustrated Biochemistry 27th Edition, Page 21-24; The Protein Protocols Handbook edited by John M. Walker, 1996, Page 215.", 'role': 'assistant'}]