Abstract: There is provided a method of determining the solubility of a chemical compound containing one or more acidic or basic groups. The method involves preparing a close to saturated solution with solid present of said chemical compound; measuring the pH of the test solution at regular intervals until a consistent rate of pH change; adding a known aliquot of base or acid titrant to the test solution to adjust the pH slope; and repeating steps (b) and (c) until the measured pH slope changes sign. The solubility of the compound is determined as the concentration of unionised compound in solution when the measured pH slope is interpolated to zero.