Proteins are the building blocks of life. All the major processes in body are regulated by one or the other protein. Therefore, it becomes very vital to assess proteins in a professional manner, for which many sophisticated techniques and protocols are available. The standard protein assessment protocol includes: Purification, Digestion, and Sequencing. Based on the provided information and knowledge of protein assessment methods, answer the following question:

Which of the following is not a method for protein purification?