Then 5 ml of chilled acetone was added to it, and the tube was held for 15 min with occasional shaking at 4 1 C, vortexed at high speed for 10 min, and finally centrifuged at 1370 g for 10 min. Supernatant was collected into a separate test tube, and the compound was re-extracted with 5 ml of an acetone followed by centrifugation once again as above.