The common assumption of considering external mass transfer resistance as negligible can lead to a systematic bias that underestimates the actual diffusivity value. In this context, the suitability of two methods and the possible experimental setups (global or local concentration measurements) for determination of both diffusivity and mass transfer coefficient are discussed. The assessment was based on the experimental results of the desorption of Uvitex OB from low density polyethylene into the food simulant Miglyol 829. A practical identifiability analysis performed for each of the methods and experimental setups demonstrated that the increased amount of information provided by local measurement methods allows a better identifiability of the parameters, thereby reducing the experimental work and providing an unbiased method for determination of diffusivity.