A fast liquid chromatography–mass spectrometry (LC–MS) method for quantification of major polar metabolites in plants

Current liquid chromatography (LC) based methods for the analysis of polar plant metabolites require multiple runs using complex mobile phases and a combination of different columns. Here we describe a fast liquid chromatography–mass spectrometry (LC–MS) method for the determination of major polar metabolites in plants that requires only a single run using a single column. The method takes advantage of the ability to acquire both positive and negative data in an ion trap mass spectrometer (MS) and also the accurate mass capability of the orbitrap MS. The separation of polar compounds is achieved with a polar, reversed-phase column (Synergi Hydro-RP). A single analysis with a 25 min runtime is able to reliably determine the level of nearly all essential amino acids, several major organic acids and several major sugars in plant materials, as exemplified by analysis of a perennial ryegrass extract. The level of detection on column was below 0.1 ng (average 0.03 ng) for most amino acids, below 5 ng (average 2.3 ng) for organics acids and below 1 ng (average 0.64 ng) for sugars. The levels of quantified metabolites in ryegrass varied from 22 μg/g dry weight for histidine to 41 mg/g dry weight for sucrose.