Enantiomer ratios for apportioning two sources of chiral compounds

A relationship is derived for estimating the contribution of chiral compounds from two sources A and B in an A-B mixture. The apportionment equation requires only the enantiomer ratios of the two sources and the resultant mixture (ERa, ERb, ERm) and corrects an erroneous relationship that was previously published. The use of ERs to apportion two sources was tested using synthetic mixtures of nonracemic (A) and racemic (B) heptachlor-exo-epoxide (HEPX). ER values for the two source types and the mixture were determined by capillary gas chromatography on a chiral cyclodextrin column with detection by negative ion mass spectrometry. Results calculated for the fraction of the nonracemic component in the mixture (F-a) using the ERs agreed with the actual composition within +2.1 to -9.8%. The average error was -2.5%, and the propagated relative standard deviation in F-a was 4-6%. ER values can be determined with high precision and are not affected by analytical method recoveries nor by abiotic processes that take place during transport. These advantages make ERs especially attractive for source apportionment.