In general the powder form of the lipid is the most stable for storage, however, unsaturated lipids form hygroscopic powders which cannot be easily weighed. Therefore saturated lipids can be purchased as powders while unsaturated lipids should be purchased as the chloroform solution. If the lipid will be stored for an extended period of time, you may want to purchase the powder form for storage then dissolve the powder using chloroform when ready to use. To use the chloroform solution, aliquot a known amount of lipid (using stainless steel, glass, or teflon — DO NOT USE PLASTIC TUBES OR PIPET TIPS) into a glass vial and evaporate the chloroform using nitrogen or argon. The lipid film can be hydrated or resuspended in an appropriate solvent for lyophilization (see bulletin on Preparation of Liposomes).