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 (T(G)) of Eudragit RS membranes was investigated using differential scanning calorimetry (DSC). The T(G)-decreasing effect of TEC and Tween 80 displayed an almost identical performance in extent at a linear relationship between weight proportion and T(G) resulting in a specific T(G)-decrease (T(G,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 T(G,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 T(G), 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.