Knowledge of solubility of a solute is important in industries such as pharmaceutics, foods, and cosmetics. Current methods used to measure solubility are time-consuming and labor-intensive and require a large amount of sample. Drop-based microfluidics is a powerful tool to determine solubility curves where each droplet acts as a microreactor. Benefits of this approach include less consumption of sample and flexible manipulation of drop volumes and composition.      We develop a microfluidic device that allows rapid generation of arrays of immobilized droplets and assess the capability of the device to measure solubility curves of inorganic salts. Droplets of volume 200 nL and a given potassium nitrate concentration are stored in the drops, followed by a thermal quenching and heating cycle. As temperature is lowered to the solubility limit, the salt inside droplets starts crystallizing. The temperature when all droplets contain crystals is recorded as the lower bound of solubility (super saturation curve). On the completion of crystallization, temperature is slowly increased to dissolve the crystals, and the temperature at which no crystal is detected is recorded as dissolution point (super solubility curve). By repeating these measurements at various salt concentrations in the same device, we recover the solubility curve of potassium nitrate, which is in good agreement with literature data.  We also design a droplet-based device that allows simultaneous screening of multiple concentrations of salt enabling rapid determination of high-resolution solubility curves.

Rapid generation of solubility curves using drop-based microfluidics

247th National Meeting (2014)

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