“Kinetically Limited” Differential Centrifugation As An Inexpensive and Readily Available Alternative to Centrifugal Elutriation

When one desires to separate two species with similar densities, but differing sedimentation velocities (due to differences in size), Centrifugal Elutriation, a method requiring specialized equipment, is the usual method of choice. We present here a method for achieving similar separations that can be realized using standard benchtop centrifuges. It involves loading the seperands as a layer on top of a denser buffer of a specified length, and running the benchtop centrifugation process for a calculated amount of time that ensures that all of the faster moving species are collected at the bottom, while all of the slower moving species remain in the buffer. We demonstrate the use of this procedure to isolate bacteria from Blood Culture Broth (a mixture of bacterial growth media, blood and bacteria).