Fractionation of bone-marrow cells by counter-current distribution in aqueous polymer two-phase systems. Relation between settling time and the efficiency of separation.

The fractionation of heterogeneous populations of rat and human bone-marrow cells has been studied by counter-current distribution in a charged 5% dextran-4% poly(ethylene glycol) two-phase system. The subfractionation into two broad populations has been achieved at a low top/bottom phase volume ratio by increasing (up to 20 min) the settling time allowed for the phases to be separated after each mixing step. No effect of this parameter on a homogeneous population of erythrocytes has been observed. However, heterogeneous cell separations can be improved by exploiting different phase settling times.