Polyacrylamide gel electrophoresis (PAGE) is typically used to separate proteins according to their electrophoretic mobility which is determined by molecular weight, conformation, and charge. Negatively charged proteins migrate across the gel towards the positive electrode at a rate that is dependent on the degree of the negative charge as well as the size of the proteins. Samples may be analyzed natively (retains charge state) or treated with sodium dodecyl sulfate (SDS) which linearizes the proteins and normalizes their charge-to-mass ratios. This causes migration of the proteins across the gel to be driven solely by the molecular weight. SDS PAGE can be used to analyze the protein composition of environmental samples in order to identify potential biological agents. The gel bands are positively identified via Western Blot (immunoblot) analysis.