Nuclear Magnetic Resonance Method for Measuring Water Solubility of Organic Compounds

Water solubility measurements are required in drug discovery,
in
toxicological or environmental studies, and in developing industrial
processes which employ extractions or crystallizations. The gold-standard
shake-flask method is tedious and takes at least 24 h. We developed
a nuclear magnetic resonance (NMR) method for automation, which has
the same accuracy and solubility range as the shake-flask method,
but a measurement can be made faster, since the analysis does not
require separation of the phases. Samples of saturated solutions are
analyzed in the presence of excess solute, since the NMR spectra do
not show signals for the dispersed solids, and they tend to show separate
signals for the dissolved and dispersed liquids. Spectra are acquired
with water suppression, using a pulse sequence appropriate for quantitation.
A sample of water is used as the external reference, and the concentration
of the solute is determined using the PULCON relationship. An evaluation
of the method in terms of selectivity, accuracy, precision, and limit
of quantitation is presented in detail.