Is there any isotopic fractionation of nitrate associated with diffusion and advection?

We experimentally investigated the effect of the physical process of transport (diffusion and advection) on the isotopic composition of nitrate (delta N-15 and delta O-18). Strict diffusion of nitrate in water was studied using a modified Richter apparatus. The combination of diffusion and advection processes was followed by elution of nitrate solution onto silica gel column. No significant isotopic fractionation was observed.