Process for programming of field-flow franctionation

Claim 1

In a field-flow fractionation process wherein a carrier fluid containing a small particulate, polymeric or macromolecular sample to be separated is forced through a thin flow channel with the carrier fluid flowing in the direction of the flow axis with flow velocity and a field force or gradient is used to induce a driving force acting across the thin channel perpendicular to the flow axis, the improvement comprising holding the field strength S of the field force constant at an initial level S o for a time lag period t 1 , and then decaying the field strength with time t according to the equation ##EQU8## where t≧t 1 >t a , t 1 ≧0 and p>0, and holding the mean channel flow velocity <v> constant at an initial level <v> o for a time-lag period t 2 and then increasing the flow velocity with time t according to the equation ##EQU9## wherein t≧t 2 >t b , t 2 ≧0 and q<0, with the above symbols representing the following S=field strength S o =field strength at initial constant level t 1 =time lag period which is time for field strength held constant t=time for decaying field strength t a =remaining time parameter when decaying field strength p=number of power when decaying field strength <v>=mean flow velocity <v> 0 =initial mean flow velocity t 2 =time lag period which is time for holding flow velocity constant t b =remaining time parameter with increasing flow velocity q=number of power when increasing flow velocity.