 The effective concentration of PMSF is between 0.1 - 1 mM.The half-life is short in aqueous solutions (110 min at pH 7, 55 min at pH 7.5, and 35 min at pH 8, all at 25 °C).Stock solutions are usually made up in anhydrous ethanol, isopropanol, or corn oil and diluted immediately before use.