Many substances or materials exist as compounds or mixtures. The diversity of life is reflected by the enormous number of molecules found in living organisms. For example, proteins or nucleic acids (DNA) exist in cells with other substances such as lipids, carbohydrates, salts, etc. Proteins or nucleic acids may also be a mixture of different types or molecular weights. In biochemistry, some of the main aims are to understand and describe the structural basis of biological molecules as they relate to function. If these molecules are to be studied, they must be purified and isolated. There are millions of proteins found in living organisms, which make the isolation of a single protein molecule a tedious and timeconsuming task.