The invention relates to a method for stabilising fatty acids present in a sample such as bodily fluids (e.g. blood, saliva, breast milk, urine, semen, blood plasma and serum), using a solid medium (such as paper, a glass-based matrix, a paper-based matrix, a cellulose-based matrix, hydrophilic polymers, polytetrafluoroethylene, fibreglass and porous ceramics) comprising chelating agents (e.g. ethylenediamine-tetraacetic acid, ascorbic acid, citric acid, or salts thereof), antioxidants (e.g. butylated hydroxytoluene, butylated hydroxyanisole or t-butylhydroquinone) and less than than about 2 &mu；g/cm2 of contaminants which is capable of stabilising fatty acids applied thereto, and a method for preparing such media. The invention further relates to a method for determining the fatty acid composition of a sample stored on such a medium.
