Abstract
The effect of various additives used in pharmaceutical formulations (inorganic salts, QABs, amino acids, sugars, alcohols, ureas) has been seen by studying the clouding phenomenon of imipramine hydrochloride (IMP) drug in solution. At fixed pH values, increasing inorganic salt concentrations caused an increase in the cloud point (CP) of 100 mM IMP prepared in 1 mM CTAB + 10 mM SP buffer solution: the magnitude of increase being dependent upon the position of the salts in Hofmeister series and hydrated radii. The addition of increasing amounts of quaternary ammonium bromides (QABs) also caused continuous increase in CP, which is explained on the basis of alkyl chain length of the particular QAB. All amino acids increased the cloud point but to different extent. While short chain alcohols affected the CP insignificantly, higher ones decreased it but medium chain alcohols showed maxima. All sugars caused a decrease in CP due to their water structure making property. Urea and alkylureas decreased the CP, which is explained on the basis of their water replacing ability from the micellar head group region. Thioureas increased the CP: however, the presence of an alkyl group had a similar effect as in alkylureas. The overall behavior has been discussed on the basis of electrostatic repulsion/interaction, micellar growth, and mixed micelle formation. (C) 2012 Elsevier B.V. All rights reserved.