<prompt> Protein purification and separation is done by all ExceptChromatographyPrecipitationElectrophoresisDensitometry  <response>: Highly purified protein is essential for the detailed examination of its physical and functional propeies. It may require the successive application of multiple purification techniques. Selective precipitation exploits differences in relative solubility of individual proteins as a function of pH isoelectric precipitation, polarity precipitation with ethanol or acetone, or salt concentration salting out with ammonium sulfate. Chromatographic techniques separate one protein from another based upon the difference in their size size exclusion chromatography, charge ion-exchange chromatography, hydrophobicity hydrophobic interaction chromatography, or ability to bind a specific ligand affinity chromatography.The most widely used method for determining the purity of a protein is SDS-PAGE--polyacrylamide gel electrophoresis PAGE in the presence of the anionic detergent sodium dodecyl sulfate SDS.Densitometry is a method to quantify the proteinsRef: Harper; 30th edition; Pg: 26 