BIFURCATION IN LIQUID DENSITY-GRADIENT CENTRIFUGAL SEPARATIONS

The liquid centrifuge using a density-gradient method has certainly pl ayed an essential role in almost every advance in molecular and cellul ar biology. For the velocity-sedimentation method, when a rotor reache s its full speed, the density-gradient solution establishes its stable profile and particles of the sample begin to separate and to form the ir respective bands, and to sediment toward the wall of rotor. While p articles move outward in bands, some of the bands separate into more b ands during sedimentation and sometimes the separated bands overtake a nd cross each other depending on local properties such as density, dis persion coefficient, particle size, etc. Then each band starts to sepa rate and to sediment outward until reaching its respective isopycnic z one. The locations where the separated bands cross each other or combi ne together may be termed bifurcation point(s) in density-gradient cen trifugation. The method of Poincare's bifurcation analysis together wi th numerical simulation are used to analyze the effect of various loca l properties on bifurcation point(s). It is found that a major factor in having bifurcation(s) is the steepness of the density-gradient prof ile. The other properties are minor. (C) 1997 Elsevier Science B.V.