A method for simultaneous determination of glucosamine (GlcN) and glucosamine 4-phosphate (GlcN-4-P) in Lipid A with high-performance anion-exchange chromatography (HPAEC) is described. Lipid A is hydrolyzed with 4 M HCl for 16h at 100 o C, and the peaks of glucosamine and glucosamine 4-phosphate were measured. The true GlcN value can be computed from the GlcN value after correction for the incomplete hydrolysis of GlcN-4-P, or by the combined yield of GlcN and GlcN-4-P.Abbreviations: LPS, lipopolysaccharides; Kdo,3-deoxy-d-manno-2-octulosonic acid; HPAEC, high performance anion exchange chromatography; GlcNAc-1-P. N-acetyl-α-d-glucosamine-1-phosphate.;GlcNAc-6-P; N-acetyl-glucosamine 6-phosphate; Man-6-P, mannose 6-phosphate; MeGlcNAc-4-P, methyl 2-acetamido-2-deoxy-4-o-phosphoryl-β-d-glucopyranoside.