A protocol has been developed for the preparation of isotopically char
acterized internal standards for compound-specific isotope analysis. F
atty acids and their corresponding methyl esters are loaded into flame
seal vials by a protocol carefully designed to minimize isotopic frac
tionation and contamination. Carbon isotope analysis of randomly selec
ted vials yields isotopic precision with an average standard deviation
of 0.09 parts per thousand (delta(13)C(PDB)). Absolute values for car
bon isotope ratios are determined against an international standard (N
IST RM8541: USGS24). The procedure is general and may be used for all
compounds soluble in volatile solvents. The fatty acid and fatty acid
methyl esters standards developed here will be useful for day-to-day q
uality control and assessment of derivative carbon addition due to met
hylation of fatty acids.