A well-developed classical theory is available for constant-voltage electrical field flow fractionation (EFFF). Recent experimental research, however, has demonstrated that pulsed fields may enhance retention in some cases. A generalized mathematical approach is presented for the prediction of retention ratios for any field type, pulsed or constant. The methodology is applied and demonstrated for a square wave protocol. Complex concentration profiles arise wherein particles are focused either towards the walls or into the channel center. The computational results indicate that pulsation can either increase retention time or decrease retention time by manipulating the effective electric field and suggest that separation resolution may also be improved.