Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a monosaccharide with a nine-carbon backbone. N-glycolylneuraminic acid (Neu5Gc or NGNA) is not synthesized in the human body, so most of the sialic acid in the body is N-acetylneuraminic acid (Neu5Ac or NANA), while other animals have two kinds of sialic acid (NANA and NGNA). There may be NGNA in biotech products manufactured from nonhuman animal source, and a detectable method is needed to determine the derivatives of sialic acid in the product.