LC-MS characterization of trace impurities contained in calcium folinate

An impurity present in calcium folinate (N5-formyl-5,6,7,8-tetrahydrofolic calcium salt) active pharmaceutical ingredient (API) was detected by high-performance liquid chromatography (HPLC). Through analysis by HPLC coupled with atmospheric-pressure chemical-ionization mass spectrometry (APCI-MS), a structure for this impurity was postulated and then proved by chemical synthesis.