In archaeological studies, the isotopic enrichment values of carbon and nitrogen 
in bone collagen give a degree of information on dietary composition. The 
isotopic enrichments of individual amino acids from bone collagen and dietary 
protein have the potential to provide more precise information about the 
components of diet. A limited amount of work has been done on this, although the 
reliability of these studies is potentially limited by fractionation arising 
through hydrolysis of whole plant tissue (where reaction between amino acids and 
carbohydrates may occur) and, for certain amino acids, the use of derivatives 
(particularly trifluoroacetyl derivatives) for gas chromatography/isotope ratio 
mass spectrometry (GC/IRMS) analysis. The present study takes the approach of 
extracting the protein components of plant tissues before hydrolysis and using 
liquid chromatography/isotope ratio mass spectrometry (LC/IRMS), which does not 
require derivatisation, for measurement of the isotopic enrichment of the amino 
acids. The protocol developed offers a methodology for consistent measurement of 
the δ(13)C values of amino acids, allowing isotopic differences between the 
individual amino acids from different plant tissues to be identified. In 
particular, there are highly significant differences between leaf and seed 
protein amino acids (leaf minus grain) in the cases of threonine (-4.1‰), 
aspartic acid (+3.5‰) and serine (-3.2‰). In addition to its intended 
application in archaeology, the technique will be of value in the fields of 
plant sciences, nutrition and environmental food-web studies.