title: Percolation theory, conductivity and dissolution of hydrophilic suppository bases (PEG systems).
abstract: We investigated the conductivity of binary mixtures of different volume to volume ratios of liquid polyethylene glycol 200 (PEG 200) and solid PEG 6000. The conductivity was measured using a specially designed cell, which could be filled with the sample to be analysed. The results were analysed by the help of the percolation theory and its basic equation: X=S(p-p(c))(q) with X=gamma the conductivity and X=k the dissolution rate constant of binary mixtures with p the concentration of PEG 200 including Mepyraminmaleat as a marker substance. The intrinsic dissolution rate was determined spectrophotometrically. The simultaneous determination of the critical exponent q and the percolation threshold p(c) of the conductivity experiment yielded the following values q=1.83+/-0.05 and p(c)=11.6+/-1.1% with a squared correlation coefficient R(2)=0. 9986. For q=mu=2.00 fixed the percolation threshold is equal to p(c)=8.4+/-1.3% with R(2)=0.9984. Thus if the same percolation threshold p(c)=8.4+/-1.3% is adopted for the dependence of the dissolution process q becomes equal to q approximately mu=1. 94+/-0.045. R(2)=0.9991. This result is in excellent agreement with the theoretical prediction that the permeability of a porous network scales in the same way as the conductivity.
authors.affiliation: Pharmaceutical Institute University of Basel, Department of Pharmacy, University of Basel, Totengässlein 3, CH-4051, Basel, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Siegmund
authors.forename: H
authors.initials: H
authors.lastname: Leuenberger
mesh_terms: D004058:Diffusion; D004339:Drug Compounding / Q000295:instrumentation / Q000379:methods; D004553:Electric Conductivity; D005079:Excipients / Q000737:chemistry; D008962:Models, Theoretical; D011092:Polyethylene Glycols / Q000737:chemistry*; D012044:Regression Analysis; D012995:Solubility; D013488:Suppositories / Q000737:chemistry
chemical_list: D005079:Excipients; D013488:Suppositories; D011092:Polyethylene Glycols