The odd-chain or isotopic labeled non-endogenous standards were used as internal standards for the quantitation of endogenous acyl-CoA species. C2:0( 13 C2)-CoA was used for the quantitation of short-chain species, C7:0-CoA was used for the quantitation of medium-chain species while C15:0-CoA and C17:0-CoA were used for the quantitation of long-chain species.