  We describe a microfluidic platform for solid phase screening using extremely
small quantities of raw materials. Based on our previous setup for solubility
measurement that generates saturated solutions directly from powder, the
platform requires no solution in excess of that used for the
droplet-crystallization experiment. The setup is compatible with most solvents
and molecules without using surfactant. Using this microfluidic platform, we
first measured the solubility of Sulfathiazole in water, isopropanol, and
acetonitrile. Second, we performed a polymorph screening of Sulfathiazole using
as little as 30 mg of raw material, for numerous identical cooling
crystallization experiments from 80 to 10{\textdegree}C. In the experiments
presented, we obtained the 3 usual polymorphs of Sulfathiazole. We show that
this economical approach yields reliable information on the probability of
nucleation of a given polymorph, useful in pharmaceutical development.
