Determination of Nonylphenol in Selected Foods and Identification of Single Isomers in a Coffee Sample by Comprehensive Two-Dimensional Gas Chromatography-Time of Flight Mass Spectrometry

Nonylphenols (NPs) are a degradation product of nonylphenol ethoxylate surfactants, which occur in many samples from the environment, food, and human organism. NPs are persistent and toxic and exhibit estrogenic activity. One of the challenges in understanding the estrogenic effects of NPs is the large number of isomers that may exist in different samples. After analyzing selected foods from different countries by high-performance liquid chromatography coupled with tandem mass spectrometry, NPs were detected in 8 of the 12 food samples. The concentration of NPs, based on fresh weight, ranged from 0.5 to 18.9 mu g kg(-1). The highest NP contents were found in coffee samples, and therefore an isomer-specific analysis was carried out by comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GCxGC-TOF-MS). Fourteen pure isomers of NP were used as standards for cross-referencing the NP isomers. We identified the two main NP isomers in the coffee samples as 4-[3-ethyl-1,1-dimethylpentyl]-phenol and 4-[1-ethyl-1,3-dimethylpentyl]-phenol or NP128 and NP111 (Juelich nomenclature), respectively. The GCxGC-TOF-MS system with a liquid nitrogen cryogenic modulator used in this study is suitable for the isomer-specific analysis of NP and can be applied and further optimized for future routine analysis in food control.