The Effect of pH on the Liquid-liquid Equilibrium for a System Containing Polyethylene Glycol Di-methyl Ether and Tri-potassium Citrate and its Application for Acetaminophen Separation

In this work liquid-liquid equilibrium for aqueous two phase system composed of polyethylene glycol di-methyl ether and tri-potassium citrate at different medium pH values (6.00, 7.00 and 8.00) and 298.15 K was studied. The obtained results show that two phase area expanded with an increasing of pH values. The performances of the Merchuk and semi-empirical equations were tested in correlating the obtained binodal data. The reliability of the experimental tie-lines was checked using the Hand and Bachman equations. Then, this two-phase system has been used to investigate partitioning of acetaminophen by determining the composition of coexisting phases in presence of acetaminophen. Experimental results show that 60-80% of the drug could be extracted into the polymer-rich phase in a single-step separation. The partitioning coefficient of acetaminophen was changed slightly with the increase of length tie-line (TLL) and also with the increase of pH values. Thermodynamic studies indicated that hydrophobic interactions were the main driving force, although electrostatic interactions and salting-out effects were also important for the transfer of the drug. Finally, the equation proposed by Diamond-Hsu was used to the correlating of the experimental partition coefficients of acetaminophen in the studied polymer- salt ATPS.