In a diffusion cell experiment, the presence of a film diffusion resistance, in series with intrapellet diffusion, leads to loss of precision in the estimation of intrapellet diffusivities. A general strategy, extendable to other problems, for quantifying a parametric region where film diffusion resistance can be neglected is studied. The results obtained from different criteria, using both moment and time domain analysis, are compared and discussed. The optimization of the experimental system in terms of maximizing the measurement's sensitivity towards the estimated parameter is also addressed, and general considerations for the optimum design of a diffusion cell system are drawn.