Chapter 25 Direct Analysis of Underivatized Amino Acids in Plant Ectract by LC-MS-MS

Abstract

In this chapter, we describe a method for quantifi cation of 20 proteinogenic amino acids as well as 13 15 N-labeled amino acids by liquid chromatography–mass spectrometry without the need for derivatization and use of organic solvents. Analysis of the underivatized amino acids is performed by liquid chromatography– electrospray ionization-tandem mass spectrometry (LC-ESI-MS-MS) in the positive ESI mode. Separation is achieved on a strong cation exchange (SCX) column (Luna 5 μ m SCX 100 Å) with 30 mM ammonium acetate in water (A) and 5% acetic acid in water (B). Quantifi cation is accomplished by use of d 5 -phenylalanine as internal standard achieving limits of detection of 0.1–3.0 μ M. The method was successfully applied for the determination of proteinogenic and 15 N-labeled amino acids in plant extracts.