This fatty acid methyl ester is ideal as a standard and for biological systems. Heptanoic acid is an odd-numbered mediumchain fatty acid that occurs only in small amounts in most biological systems and is therefore ideal as an internal standard. Being a medium-chain fatty acid it can enter easily into cells across the cell membrane and is therefore often found esterified to synthetic drugs.1 Although heptanoic acid itself contributes to the rancid smell of cooking oils2 some esters of heptanoic acid have been used in fragrances and artificial flavors.3 Genetic disorders of the mitochondria long-chain fatty acid betaoxidation pathway can result in the accumulation of toxic long-chain fatty acid oxidation products; Medium-chain fatty acid triglycerides containing both even and odd-numbered fatty acids have been shown to be able to decrease the build-up of these long-chain fatty acid oxidation products.4
