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 an aqueous two phase system composed of polyethylene glycol di-methyl ether and tripotassium citrate at different medium ph values (6.00, 7.00 and 8.00) and 298.15 k was studied. the results showed that the two-phase area expands with increasing ph values. the performances of the merchuk and semi-empirical equations were examined in correlating the obtained binodal data. the reliability of the experimental tie-lines was verified using the hand and bachman equations. then, this twophase system was used to investigate partitioning of acetaminophen by determining the composition of coexisting phases in the presence of acetaminophen. experimental results showed 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 tie-line length 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 drug transformation. finally, the equation proposed by diamond-hsu was used to the correlating of the experimental partition coefficients of acetaminophen in the studied polymer- salt aqueous two-phase system.