Methylcobalamin, S-Adenosyl-L-methionine, 2-hydroxyethyl phosphonic acid, and 2-hydroxy propyl phosphonic acid were separated in reversed-phase anion-exchange mixed-mode on a Primesep SB HPLC column. Compounds are monitored by UV and ELSD. Method is compatible with LC/MS. Selectivity of separation is controlled by varying the amount of ACn buffer pH and buffer concentration.