Principles and applications of broadband acoustic resonance dissolution spectroscopy (BARDS): a sound approach for the analysis of compounds

The dissolution of a compound results in the introduction and generation of gas bubbles in the solvent. This formation is due to entrained gases adhered to or trapped within the particles. Furthermore, a reduction in gas solubility due to the solute results in additional bubble generation. Their presence increases the compressibility of the solvent with the added effect of reducing the velocity of sound in the solvent. This effect is monitored via the frequency change of acoustic resonances that are mechanically provoked in the solvent and are now used as an insightful analytical technique. An experimental set up was designed to study a large number of compounds as a function of time, concentration, and solvent system. This revealed the role of the various physical and chemical mechanisms in determining the observed response. It is also shown that this response is strongly dependent on the physical and chemical characteristics of the solute compound used, therefore resulting in a method for the characterization of compounds and mixtures. Additional factors such as morphology (polymorphism), particle size, and dissolution rate are shown to be key in the variation of the resulting response. A mathematical model has also been developed in parallel, which inter-relates the various processes involved in the observed response. It is anticipated that BARDS will open up a new window into transient dissolution processes and compound characterization.