title: A novel method for determining the solubility of small molecules in aqueous media and polymer solvent systems using solution calorimetry.
abstract: OBJECTIVE
  To explore the application of solution calorimetry for measuring drug solubility in experimentally challenging situations while providing additional information on the physical properties of the solute material.
  
  
  METHODS
  A semi-adiabatic solution calorimeter was used to measure the heat of dissolution of prednisolone and chlorpropamide in aqueous solvents and of griseofulvin and ritonavir in viscous solutions containing polyvinylpyrrolidone and N-ethylpyrrolidone.
  
  
  RESULTS
  Dissolution end point was clearly ascertained when heat generation stopped. The heat of solution was a linear function of dissolved mass for all drugs (<10% RSD, except for chlorpropamide). Heats of solution of 9.8 ± 0.8, 28.8 ± 0.6, 45.7 ± 1.6 and 159.8 ± 20.1 J/g were obtained for griseofulvin, ritonavir, prednisolone and chlorpropamide, respectively. Saturation was identifiable by a plateau in the heat signal and the crossing of the two linear segments corresponds to the solubility limit. The solubilities of prednisolone and chlopropamide in water by the calorimetric method were 0.23 and 0.158 mg/mL, respectively, in agreement with the shake-flask/HPLC-UV determined values of 0.212 ± 0.013 and 0.169 ± 0.015 mg/mL, respectively. For the higher solubility and high viscosity systems of griseofulvin and ritonavir in NEP/PVP mixtures, respectively, solubility values of 65 and 594 mg/g, respectively, were obtained.
  
  
  CONCLUSIONS
  Solution calorimetry offers a reliable method for measuring drug solubility in organic and aqueous solvents. The approach is complementary to the traditional shake-flask method, providing information on the solid properties of the solute. For highly viscous solutions, the calorimetric approach is advantageous.
authors.affiliation: Department of Industrial & Physical Pharmacy, College of Pharmacy, Purdue University, 575 Stadium Mall Drive, West Lafayette, Indiana, 47907, USA.
authors.forename: Hala M
authors.initials: HM
authors.lastname: Fadda
authors.forename: Xin
authors.initials: X
authors.lastname: Chen
authors.forename: Aktham
authors.initials: A
authors.lastname: Aburub
authors.forename: Dinesh
authors.initials: D
authors.lastname: Mishra
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Pinal
mesh_terms: D002151:Calorimetry / Q000379:methods*; D002747:Chlorpropamide / Q000737:chemistry; D006118:Griseofulvin / Q000737:chemistry; D019999:Pharmaceutical Solutions / Q000737:chemistry*; D011205:Povidone / Q000737:chemistry; D011239:Prednisolone / Q000737:chemistry; D011760:Pyrrolidinones / Q000737:chemistry; D019438:Ritonavir / Q000737:chemistry; D012995:Solubility; D012996:Solutions; D012997:Solvents / Q000737:chemistry; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: C523727:N-ethyl-2-pyrrolidone; D019999:Pharmaceutical Solutions; D011760:Pyrrolidinones; D012996:Solutions; D012997:Solvents; D014867:Water; D006118:Griseofulvin; D011239:Prednisolone; D011205:Povidone; D019438:Ritonavir; D002747:Chlorpropamide