DEPC treatment (from Ambion web site)

Diethylpyrocarbonate (DEPC) treatment is the most commonly used method for eliminating RNase contamination from water, buffers, and other solutions. DEPC destroys enzymatic activity by modifying -NH, -SH and -OH groups in RNases and other proteins. When DEPC breaks down during autoclaving, a small amount of ethanol is produced. The ethanol can combine with trace amounts of carboxylic acid to produce volatile esters, which give off this characteristic smell. This is not a sign of incomplete DEPC removal and it will not interfere with any subsequent reactions.

Reagents containing primary amine groups (e.g., Tris and EDTA) and some reagents containing secondary or tertiary amines (e.g., HEPES) cannot be DEPC-treated. The amine groups tend to react with and "sop up" the DEPC, making it unavailable for inactivating RNases (see Technical Bulletin 178). Also, modification of the reagent's amine groups could affect its buffering capability. Solutions that cannot withstand autoclaving and thus need to be filtered, such as MOPS, also cannot be DEPC-treated since autoclaving is essential for inactivating DEPC. In these cases, use clean reagents and DEPC treated water to make up the solution.

To treat solutions with DEPC, add 0.1% DEPC, mix and let sit at room temperature O/N. Then autoclave.