An interferometric method for low-speed equilibrium sedimentation at low initial concentrations

• Published in: Analytical biochemistry Vol. 43; no. 1; pp. 7 - 14
• Main Author: Li, Lu-Ku
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.09.1971
• Subjects: Crystallins; Mathematics; Methods; Molecular Weight; Optics and Photonics; Ovalbumin; Statistics as Topic; Ultracentrifugation
• ISSN: 0003-2697; 1096-0309
• DOI: 10.1016/0003-2697(71)90101-1

A method is described for determining initial concentrations between 0.2 and 1.0 mg/ml in the ultracentrifuge using the interference optics. The method makes use of the equations describing the conservation of mass when the concentration at the meniscus of the solution column is negligible. The latter condition is met by centrifuging the rotor at speeds 3× greater than the estimated equilibrium speed for about one hour. The interference pattern thus obtained described the concentration distribution ( f) of the solute along the axis of rotation ( r). The total mass is readily calculated from the integral ∫ r m r b f dr 2 Since the volume of a sector-shaped cell is proportional to r 2, dividing the integral by r b 2 − r m 2 yields f 0, the initial concentration in mm of fringe displacement. Application of this overspeeding procedure either at the beginning or at the end of a low-speed equilibrium run allows the routine estimation of various average molecular weights at low initial concentrations.