DETERMINATION OF LOW-MOLECULAR-WEIGHT DICARBOXYLIC-ACIDS IN ROOT EXUDATES BY GAS-CHROMATOGRAPHY

Many high-pressure liquid chromatographic methods used for the determi nation of low molecular weight organic acids in root exudates lack spe cificity and cannot completely separate mixtures of mono-, poly-, and hydroxycarboxylic acids simultaneously. Hence, a new gas chromatograph ic (GC) method that is specific for the identification and quantitatio n of low molecular weight dicarboxylic acids as methyl esters was deve loped. Samples collected from root exudates of selected durum wheat an d nax cultivars grown in sterile hydroponic solutions were extracted a nd concentrated by anion exchange membranes. Samples were then subject ed to methylation in acidified methanol at elevated temperatures and i njected into a GC. The five acids investigated in this study-oxalic, m alonic, succinic, fumaric, and maleic-required 7 min for elution from a GC column and were quantified using methylmalonic acid as an interna l standard. Good recovery and reproducibility as well as a low detecti on limit of ca. 1 ppm acid in the membrane eluate make this method ver y suitable for dicarboxylic acid determination in root exudates.