CONDENSED-PHASE CARBON ISOTOPIC STANDARDS FOR COMPOUND-SPECIFIC ISOTOPE ANALYSIS

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.