Comparison of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry spectra obtained from released N-glycans from serum proteins after linkage-specific sialic acid esterification and HILIC enrichment. The shown spectra are derived from an individual with rheumatoid arthritis who has been diagnosed with ACPA and RF, and has been classified as a responder by the EULAR response criteria. Notable differences between the first trimester (top) and third trimester (bottom) spectra include galactosylation (e.g., between m/z 1,485.5, 1,647.6, and 1,809.6), antennarity (e.g., m/z 2,940.1 vs. 2,301.8), α2,3-linked sialylation (e.g., m/z 2,255.8 vs. 2,301.8), and α2,6-linked sialylation (e.g., m/z 1,982.7 vs. 2,301.8).