Kinetic/Thermodynamic Solubility

Solubility represents an important parameter during pharmaceutical research and development, where it translates directly into their pharmacokinetics, pharmacodynamics and toxicodynamics. Solubility is a significant parameter in the biopharmaceutical classification schemes (BCS) of therapeutic compounds.

In addition to obtaining early prediction of in vivo behavior of the compound, estimation of solubility in early phase of discovery is also important with respect to quality of other target-based assays conducted concurrently.

Solubility is usually determined in one of the two approaches: thermodynamic or kinetic solubility. Thermodynamic solubility refers to traditional method wherein the compound is weighed in a particular solvent (buffer) and dissolved analyte is measured after reach equilibrium. Kinetic solubility is determined by preparing a concentrated stock solution (10 mM) in an organic solvent (usually DMSO), after which the solution is diluted in an aqueous buffer (eg. PBS) to a desired concentration. In both cases, solubility can be determined by HPLC-UV or LC-MS/MS after filtration or spin-down to remove the insoluble.

Kinetic solubility offers a high-throughput method with relatively small amount of compound, especially useful in the early discovery phases. Thermodynamic solubility is typically performed during the latter stages of drug discovery or early development, and may help to design formulation strategies for in vivo studies.

Assay Methodology

At Quintara Discovery, Kinetic solubulity for test compounds is routinely measured in aqueous buffer when added from an existing stock solution in DMSO. The assay can be customized for determining solubilities of test compounds in any matrix or pH.

Solubility: Standard Assay Conditions (Customizable)

Target Compound Concentration
500 μM (kinetic); 5 mg/mL (thermodynamic)

Dynamic Range
1-500 μM

Assay Buffer
0.1 M phosphate buffered saline pH 7.4

Mixing Period
1.5 h (kinetic) and 24 h (thermodynamic) at room temperature

Sample Preparation
Centrifugation or filtration

Detection Method
HPLC with UV-vis spectrometry


Turnaround Time
2-3 Days

Compound requirements
50 μL 10 mM DMSO stock (kinetic); 5 mg solid (thermodynamic)