Core And Sialylated O-Glycan Standards O-glycosylation is a common covalent modification of serine and threonine residues of mammalian glycoproteins. The most common type of O-glycosylation found on secreted mammalian glycoproteins and mucins (proteins conjugated to carbohydrate) is from the addition of N-acytylgalactosamine (GalNac) to serine or threonine residues. The Core 1 structure is generated by the addition of galactose b1-3 to this GalNAc. The Core 2 structure is generated by the further addition of N-acetyl-glucosamine b1-6 to the N-acetyl-galactosamine on the Core 1 structure. In total eight different core structures have been identified and all of these can be further elongated by the addition of a number of monosaccharides including sialic acids. These O-glycans are present in biopharmaceuticals such as erythropoeitin (EPO), Etanercept (Enbrel) and human Factor VIII (FVIII). Core 1 and Core 2 O-glycans are also present in biopharmaceuticals such as erythropoeitin (EPO), Etanercept (Enbrel), human Factor VIII (FVIII), Factor IX and insulin glargine. Six 2-AB labelled Core 1 and Core 2 O glycan standards are now available. The standards typically have a purity of > 93% as assessed by HILIC-HPLC and can be used as internal references or system suitability standards for peak assignment during HPLC or UPLC analysis.