N-Hexane Extractable Material (HEM; Oil and Grease) and Silica Gel Treated N-Hexane Extractable Material (SGT-HEM; Non-Polar Material)
A 1-L sample is acidified and serially extracted three times with n-hexane in a separatory funnel. The extract is dried over sodium sulfate. The solvent is distilled from the extract and the residue from the extract is desiccated. The amount of HEM in the extract is measured by weighing the dry residue on a balance. If the HEM is to be used for determination of SGT-HEM, the HEM is redissolved in n-hexane and silica gel is added to remove polar materials. The solution is filtered to remove the silica gel, the solvent is distilled, and the residue is desiccated. The amount of SGT-HEM in the extract is measured by weighing the dry residue on a balance.