General Aspects
Compounds are normally stored as a stock solution to be dispensed as needed by robotic
equipment. Dimethylsulfoxide (DMSO) is a preferred solvent for several reasons. First, in
low concentrations, DMSO is well tolerated in most assays. Second, the low melting point
of DMSO (18 C) allows samples to be easily frozen. Compounds that are stored in the
solid state are less prone to decompose. Third, DMSO is less volatile than most organic
solvents. Decreased volatility minimizes solvent evaporation, so concentrations remain
nearly constant over prolonged storage. Maintaining a known concentration is vital. The
activity of each screened molecule is related by a concentration-effect relationship. If the
concentration of a stock solution is not accurate, then any subsequent assessment of activity
will also be incorrect.