Quantification of the leaching of triethyl citrate/polysorbate 80 mixtures from Eudragit® RS films by differential scanning calorimetry

The influence of triethyl citrate and polysorbate 80 (Tween® 80) on the glass transition temperature (TG) of Eudragit® RS membranes was investigated using differential scanning calorimetry (DSC). The TG-decreasing effect of TEC and Tween® 80 displayed an almost identical performance in extent at a linear relationship between weight proportion and TG resulting in a specific TG-decrease (TG,spec.) of −1.98(K/%TEC) and −1.86(K/%Tween), respectively. Thus, the proportion of each adjuvant could be summarized as the plasticizer complex weight proportion (PC) with TG,spec.=1.96(K/%PC). Vice versa this linear relationship could be used to determine the proportion of plasticizer complex within the polymer membrane after swelling and diffusion processes, i.e. plasticizer leaching. For membranes containing 20% (w/w) TEC and 8% (w/w) Tween® 80 as plasticizer complex a fast leaching resulted during the dissolution test reaching an equilibrium at 6.08% (±0.5) PC after 30 min in demineralised water. The DSC method proved to be a simple method to determine plasticizer leaching via TG, however, without respect on the film forming properties of the two different excipients. Plasticizing with TEC or TEC/Tween® 80 mixtures led to smooth and continuous films, while plasticizing with Tween® 80 only resulted in mosaic like fissured films.