A common HPLC-PDA method for amino acid analysis in insects and plants

A common method for analysis of 17 amino acids from various insect species and plant parts was standardized using HPLC-PDA. Prior to hydrolysis, lyophilization of test samples was found indispensible to remove excess moisture, which interferes in hydrolysis and separation of amino acids. After the hydrolysis of plant and insect samples, 500 and 100 microL of boiling HCl, respectively for reconstitution, and 20 microL of hydrolyzed samples used for derivatization, provided best results. Gradient profile of mobile phase and run time up to 65 min were standardized to (i) overcome the problems related to eluting underivatized sample part, (ii) optimize the use of mobile phase and run time, and (iii) get better separation of different amino acids. Analysis of Chilo partellus larvae reared on sorghum seedling powder based artificial diet indicated that arginine and histidine quantities were on par in both samples. However, methionine was higher, and leucine, isoleucine, lysine, phenylalanine, threonine and valine were lower in sorghum seedlings than in C. partellus larvae, suggesting compensation of these amino acids by the insect through voracious feeding, as is being expected from artificial diet. This method was found highly sensitive, reproducible and useful for the analysis of amino acids for better understanding of insect-plant interactions.