Micro‐FFF: Theoretical and practical aspects of reducing the dimensions of field‐flow fractionation channels

The value of miniaturizing field‐flow fractionation (FFF) channels is examined based on theoretical and experimental evidence. While FFF and chromatography are dynamically similar, the dimension analogous to capillary or particle diameter in chromatography is the Brownian excursion distance (ℓ), a "soft" dimension controlled by field strength and thus subject to significant reduction by increasing the field strength. Optimization of the “hard” channel dimensions (length, breadth, thickness) is a more complex matter involving diverse factors including sample dilution and detectability, clog‐free operation, edge effects, relaxation time, compatibility with pump and detector systems, and only in some cases the influence of these dimensions on the achievable ℓ.