A hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC-MS/MS)-based highly sensitive method utilizing limited sample volumes has been developed to analyze 5-aminolevulinic acid (5-ALA) in cell samples. Under the constructed HILIC conditions, 5-ALA is completely separated from biomolecules with similar molecular weights (leucine, isoleucine, hydroxyproline, and creatine)...