The analysis of carbohydrate moieties of glycoprotein biopharmaceuticals is of high importance, especially because glycosylation changes can impact the biological effect of the drugs. In the case of monoclonal antibody therapeutics, the degree of core fucosylation significantly influences its effector function, thus should be closely monitored during the clone selection, development and manufacturing processes. MS analysis of labile sugar residues such as core fucosylation and terminal silylation may be misleading as such residues can break off during the ionization process or alter the ionization efficiency, both of which affect the results. In the case of monoclonal antibody therapeutics tailored for antibody-dependent cellular cytotoxicity function, core fucosylation should be kept minimal; therefore, close attention should be paid to the prevalence of this particular sugar residue. This paper reports on the core fucosylation analysis of some major immunoglobulin G N-glycans by direct infusion ESI-MS and CE–LIF. In comparison to the industry standard of CE–LIF, a lower degree of core fucosylated structures was found by ESI-MS analysis, emphasizing the need to use orthogonal quantitative separation methods in addition to MS.