Mix polar and nonpolar solvent. Because of toxicity, cost, and flammability concerns, the common solvents are hexanes (or petroleum ethers, ligroin) and ethyl acetate (an ester). Diethyl ether can be used, but it is very flammable and volatile. Alcohols (methanol, ethanol) can be used. Acetic acid (a carboxylic acid) can be used, usually as a small percentage component of the system, since it is corrosive, non-volatile, very polar, and has irritating vapors. Acetone (a ketone) can be used. Methylene chloride (halogenated hydrocarbon) is a good solvent, but it is toxic and should be AVOIDED. If two solvents are equal in performance and toxicity, the more volatile solvent is preferred in column chromatography because it will be easier to remove from the desired compound after isolation from a column chromatography procedure.