A GC-ECD Method for Estimation of Free and Bound Amino Acids, γ-Aminobutyric Acid, Salicylic Acid, and Acetyl Salicylic Acid from Solanum lycopersicum (L.)
Abstract A gas chromatograph with electron capture detection method for estimation of selected metabolites—amino acids (free and bound), γ-aminobutyric acid (GABA), salicylic acid (SA), and acetyl salicylic acid (ASA) from tomato—is reported. The method is based on nitrophenylation of the metabolites by 1-fluoro-2,4-dinitrobenzene under aqueous alkaline conditions to form dinitrophenyl derivatives. The derivatives were stable under the operating conditions of GC. Analysis of bound amino acids comprised perchloric acid precipitation of protein, alkylation (carboxymethylation) with iodoacetic acid, vapor-phase hydrolysis, and derivatization with 1-fluoro-2,4-dinitrobenzene in that order. The metabolites were resolved in 35 min, using a temperature-programmed run. The method is rapid, sensitive, and precise. It easily measured the typical amino acids (aspartate, asparagine, glutamate, glutamine, alanine, leucine, lysine, and phenylalanine) used for identification and quantification of a protein, resolved amino acids of the same mass (leucine and isoleucine), satisfactorily measured sulfur amino acids (methionine, cystine, and cysteine), and quantified GABA, SA, and ASA, as well. The developed method was validated for specificity, linearity, and precision. It has been applied and recommended for estimation of 25 metabolites from Solanum lycopersicum (L.).