Notes: C17 Sphingomyelin is a synthetic derivative of sphingomyelin (Item Nos. 22674 / 24345). It has been used as an internal standard for the quantification of sphingomyelin.{41442,41443} C17 D-erythro L-threo Sphingomyelin is a mixture of D-erythro and L-threo isomers. As this product is derived from a natural source, there may be variations in the sphingoid backbone. [Matreya, LLC. Catalog No. 1890]