It has recently become clear that an isomer and enantiomer specific view of 4-nonylphenol (NP) is absolutely necessary to improve the knowledge on the biological and environmental behavior of NP. Theoretically 211 constitutional NP isomers exist. Many of these isomers possess up to three chiral C-atoms, so that in total 550 compounds are possible. Recent studies have shown that the estrogenic effects of the individual NP isomers are heavily dependent on the structure of the side alkyl chain. Additionally, log K_ow values for representative NP isomers range from 4.7 to 5.6, suggesting differences in bioconcentration potential among NP isomers. Therefore, isomer- and enantiomer-specific determination of NP is of great interest in NP research.

We developed a comprehensive chiral GC-MS method for enantioselective analysis of two chiral NP isomers, which are relative abundance in the technical NP mixture and in environmental matrices. Briefly, water samples were extracted by Liquid-liquid extraction, cleaned up by SPE, derivatized, and analyzed by chiral GC-MS. In addition, a chiral HPLC method was developed in order to obtain the enantiopure reference compounds from the racemic mixtures. These pure enantiomers of NP₁₁₂ and NP₃₅ were obtained by analytical scale preparation allowing further study on the enantioselectivity in estrogenic effects via E-Screen test.

Investigation of influent and effluent samples from a wastewater treatment plant (WWTP) in Germany were performed using the established methods. Enantiomeric determination of target isomers in the influent and effluent of the WWTP were successfully achieved. Concentrations of enantiomers of NP₁₁₂ and NP₃₅ in influent and effluent samples ranged from 13 to 1700 ng/L. In one examined influent, an enantiomer ratio of 1.7 for both isomers was determined. This result indicated that enantioselective degradation could occur in the environment. Therefore, further degradation studies will be needed to understand the enantioselectivity in degradation of chiral NP isomers.