Analysis of the Toxic Amino Acid Indospicine by Liquid Chromatography-Tandem Mass Spectrometry

Some Indigofera species contain a toxic non-protein amino acid known as indospicine. Indospicine-containing plants are toxic to livestock, and cases of secondary poisoning have been documented in dogs that consume indospicine-containing meat. For the analysis of indospicine in the plant material, a method was developed based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) of the phenylisothiocyanate derivative of indospicine. Indospicine was extracted from the plant with ethanol/0.01N HCl (70:30). The sample was then derivatized with a phenylisothiocyanate solution and then analyzed by LC-MS/MS. The method was linear over the range of 1.0-25 μg/mL, recovery was 86% and the intra-day precision was 4.7% (RSD). Indospicine was confirmed in samples of I. lespedezioides collected in Brazil with a concentration range of 60-1400 μg/g (dry weight basis). No indospicine was detected in samples of I. praticola and I. tinctoria from Zimbabwe, Africa.