Non-polar electrical field flow fractionation (Np-EFFF) has been demonstrated to separate electrophotographic toner particles suspended in hydrocarbon medium according to the ratio of their diffusivities and their electrophoretic mobilities. While electrophoretic mobility has long been recognized as critical to the behavior of liquid toner particles in a development gap, the role of diffusivity has largely been ignored. Toner particles move in the development gap as a function of both parameters, and as toner particle size is reduced to achieve improvements in print quality, diffusivity becomes increasingly important. We present a method of quantifying and predicting the behavior of toner particles in the development gap of a print engine. Particles eluting from the Np-EFFF channel at the same retention volume would be expected to exhibit similar development characteristics in a printer. Consequently, Np-EFFF retention volume data can be used to predict image development performance of liquid toner particles. Using this instrument with the multi-angle laser light scattering (MALLS) detector permits simultaneous determination of particle size, and particle size distribution. Although it is theoretically possible to determine other fundamental particle parameters from Np-EFFF data, it is used here to separate particles for further analysis down steam. In practical application, these instrumental capabilities allow screening of very small toner test batches, thus conserving time, expense, and the amount of waste generated.