This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: miscellaneous, Subject name: Biochemistry
The most widely used method for determining the purity of a protein is? 
Select and explain. 
A. Isoelectric focusing, B. Polyacrylamide gel electrophoresis, C. Ion exchange chromatography, D. High pressure chromatography
B: Polyacrylamide gel electrophoresis
Answer: B: Polyacrylamide gel electrophoresis 
Explanation: The most widely used method for determining the purity of a protein is polyacrylamide gel electrophoresis (PAGE) in the presence of an anionic detergent, sodium dodecyl sulphate (SDS). Electrophoresis separates the charged biomolecules based on the rates at which they migrate in an electrical field. Reference: Harpers illustrated biochemistry 30th edition