MECHANISTIC STUDY OF ELECTRICAL-FIELD FLOW FRACTIONATION .2. EFFECT OF SAMPLE CONDUCTIVITY ON RETENTION

Experimental work presented in this paper demonstrates that retention in electrical field-now fractionation shows a very strong dependence o n the amount of injected sample, even for very low concentrations. Thi s concentration dependence on retention is shown to result from conduc tivity differences between the colloidal particles and the carrier flu id. As a result of this concentration dependence, the electric held is a function of position inside the channel. This fact is important whe n electrical FFF is used for determining electrophoretic mobilities an d particle sizes because the analyst must be careful in interpreting t he physical origin of retention changes, Furthermore, it is shown thro ugh experiment that residual salt in the injected sample buffer can af fect retention, A transport model is developed that characterizes the relaxed zone profile; computation of these developed equations shows t he extent of deviation from the standard transverse exponential concen tration profile.