A novel mass spectrometric method to distinguish isobaric monosaccharides that are phosphorylated or sulfated using ion-pairing reagents.

Phosphorylation and sulfation are two important biological modifications present in carbohydrates, proteins, and glycoproteins. Typically, sulfation and phosphorylation cause different biological responses, so differentiating these two functional groups is important for understanding structure/function relationships in proteins, carbohydrates, and metabolites. Since phosphorylated and sulfated compounds are isobaric, their discrimination is not possible in routinely utilized mass spectrometers. Thus, a novel mass spectrometric method to distinguish them has been developed. Herein, we utilize basic peptides as ion-pairing reagents to complex to phosphorylated and sulfated carbohydrates via noncovalent interactions. By performing ESI-MS/MS on the ion-pair complexes, the isobaric compounds can be distinguished. This is the first study demonstrating that ion-pairing can be used for the detection of phosphorylated compounds and the first study to use ion-pairing in conjunction with MS/MS to obtain structural information about the analytes.