Division 5.1 Preparation of the chromatography columnF1

Suspend 15 g of silica gel (point 4.1) in n-hexane (point 4.2) and introduce into the column (point 3.2). Allow to settle spontaneously. Complete settling with the aid of an electric shaker to make the chromatographic bed more homogeneous. Percolate 30 ml of n-hexane to remove any impurities. Weigh exactly about 500 mg of the sample into the 25-ml flask (point 3.1), using the analytical balance (point 3.8), and add a suitable amount of internal standard (point 4.5), depending on the assumed wax content, e.g. add 0,1 mg of lauryl arachidate in the case of olive oil, 0,25-0,50 mg in the case of olive-pomace oil and 0,05 mg of methyl heptadecanoate for olive oils (point 4.6).

Transfer the prepared sample to the chromatography column with the aid of two 2-ml portions of n-hexane (point 4.2).

Allow the solvent to flow to 1 mm above the upper level of the absorbent. Percolate a further of n-hexane/ethyl ether (99:1) and collect 220 ml at a flow of about 15 drops every 10 seconds. ( This fraction contains the methyl and ethyl esters and waxes ). ( Note 4 ) ( Note 5 ).

Evaporate the resultant fractions in a rotary evaporator until the solvent is almost removed. Remove the last 2 ml under a weak current of nitrogen. Collect the fraction containing the methyl and ethyl esters is diluted with 2-4 ml of n-heptane or iso-octane.