Editing Centrifugation (section)

====Analytical ultracentrifugation====
Analytical ultracentrifugation (AUC) can be used for determination of the properties of macromolecules such as shape, mass, composition, and conformation. It is a commonly used biomolecular analysis technique used to evaluate sample purity, to characterize the assembly and disassembly mechanisms of [[biomolecular complex]]es, to determine subunit [[stoichiometries]], to identify and characterize macromolecular conformational changes, and to calculate equilibrium constants and thermodynamic parameters for self-associating and hetero-associating systems.<ref>{{cite journal |last1=Cole |first1=JL |last2=Hansen |first2=JC |title=Analytical ultracentrifugation as a contemporary biomolecular research tool. |journal=Journal of Biomolecular Techniques |date=December 1999 |volume=10 |issue=4 |pages=163–76 |pmid=19499023 |issn=1524-0215 |pmc=2291609}}</ref> Analytical ultracentrifuges incorporate a scanning [[Visible light|visible]]/[[ultraviolet light]]-based optical detection system for real-time monitoring of the sample’s progress during a spin.<ref name="compare">{{cite web |title=Analytical and Preparative Ultracentrifuges |url=https://www.labcompare.com/10-Featured-Articles/135690-Analytical-and-Preparative-Ultracentrifuges/ |website=www.labcompare.com |language=en}}</ref>

Samples are centrifuged with a high-density solution such as [[sucrose]], [[caesium chloride]], or [[iodixanol]]. The high-density solution may be at a uniform concentration throughout the test tube ("cushion") or a varying concentration ("[[gradient]]"). Molecular properties can be modeled through [[sedimentation]] velocity analysis or sedimentation equilibrium analysis. During the run, the particle or molecules will migrate through the test tube at different speeds depending on their physical properties and the properties of the solution, and eventually form a pellet at the bottom of the tube, or bands at various heights.