Enantiomer ratios for apportioning two sources of chiral compounds

A relationship is derived for estimating the contribution of chiral compoun ds from two sources A and B in an A-B mixture. The apportionment equation r equires only the enantiomer ratios of the two sources and the resultant mix ture (ERa, ERb, ERm) and corrects an erroneous relationship that was previo usly published. The use of ERs to apportion two sources was tested using sy nthetic mixtures of nonracemic (A) and racemic (B) heptachlor-exo-epoxide ( HEPX). ER values for the two source types and the mixture were determined b y capillary gas chromatography on a chiral cyclodextrin column with detecti on by negative ion mass spectrometry. Results calculated for the fraction o f the nonracemic component in the mixture (F-a) using the ERs agreed with t he actual composition within +2.1 to -9.8%. The average error was -2.5%, an d 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 metho d recoveries nor by abiotic processes that take place during transport. The se advantages make ERs especially attractive for source apportionment.