"Are methanol, ethanol, acetone, or acetonitrile FDA approved?"
These solvents are generally not FDA approved. These particular solvents bond plastic together by melting the plastic, and then allowing the plastics to intermingle. As the solvent evaporates, the plastics harden to form a strong plastic weld between the plastics. The choice of which grade of solvent you buy is up to the medical device manufacturer (higher purity equals higher price). Since solvents evaporate and do not remain in the bond line, they are not normally tested for biocompatibility.