Identification of α-amino acids by hydrophilic interaction chromatography-tandem mass spectrometry in fertilizers

Hydrophilic interaction chromatography with a triple quadrupole mass spectrometric detector (MS/MS) operating in a multiple reaction monitoring mode was applied for identification of 21 free a-amino acids in fertilizer samples. The electrospray ionization source (ESI) was set to positive ionization. ESI-MS/MS parameters were optimized individually for each analyte under direct standards infusion. Among three hydrophilic interaction chromatography stationary phases studied (Atlantis HILIC,Acquity BEH HILIC, and Acquity BEH Amide), the acquity BEH Amide phase showed the best performance. Complete separation of all alpha-amino acids was achieved in 15 min by gradient elution with a water/acetonitrile mobile phase containing 3 mmol/L ammonium acetate, 3 mmol/L ammonium formate and 20 mmol/L formic acid additives. The developed HILIC-MS/MS method was applied for identification of free a-amino acids in four biological fertilizer products of natural origin.