Determination of 4-octylphenol and 4-nonylphenol congeners in composite foods

A method for the determination of alkylphenols in food using cold solvent extraction with methanol, followed by a two-stage chromatographic purification and GC-MS analysis, was developed. The method was validated and used to measure concentrations of 4-octylphenol and 4-nonylphenol congener totals in UK duplicate diet samples. Individual 4-n-octylphenol and 4-n-nonylphenol congeners were also measured, although these were not detected in any sample. Only one sample showed 4-tert-octylphenol at 8.7 µg kg−1, but levels of 4-nonylphenol ranged from not detectable (<3.8 µg kg−1) to 25 µg kg−1. This concentration range is lower than that reported by others. Tests carried out on the stability of the octyl- and nonylphenol congeners in a duplicate diet matrix over 6 months suggest that some analyte depletion might have occurred during extended frozen storage, which in part may account for the relatively lower concentrations detected, although the extent of usage of these compounds also needs to be taken into consideration.