The Click-iT® O-GlcNAc peptide and phosphopeptide LC/MS standards provide 5 nmol each of a peptide from the transcription factor, CREB, (H-Thr-Ala-Pro-Thr-Ser-Thr-Ile-Ala- Pro-Gly-OH) with either the Ser residue GlcNAcylated or phosphorylated. These peptides can be used as LC/MS standards for differential mass-spectrometry-based CID and PSD studies of the corresponding modifications, as well as, for the characterization of differential conditions