Enhanced screening efficiency for endocrine-disrupting chemicals in milk and powdered milk using UPLC/QTOF-MS by the introduction of dansyl chloride derivatisation

Abstract

This study developed and validated a sensitive analytical method for simultaneous screening of four classes of endocrine-disrupting chemicals (i.e. progestogens, androgens, oestrogens and phenols) in milk and powdered milk using ultra-performance liquid chromatography (UPLC) coupled with electrospray ionisation quadrupole time-of-flight mass spectrometry (QTOF-MS). Dansylation of oestrogens and phenols enhanced the ionisation efficiency and shifted the ionisation mode from negative to positive, which allowed for the simultaneous analysis of four EDCs in one chromatographic run. An efficient sample pre-treatment minimised the matrix effects. The mass errors for the precursor and product ions for 26 target compounds varied between −2.8 and 2.3 mDa; and the limits of detection (signal-to-noise ratio = 3) for milk and powdered milk were less than 0.04 µg l⁻¹ and 0.10 µg kg⁻¹, respectively. The proposed method was successfully used to analyse multiple types of real samples, including normal temperature whole milk, infant formula and whole powdered milk. In 11 samples, two target compounds, progesterone and androstenedione, were detected. The progesterone concentrations ranged from 8.1 to 12.7 µg l⁻¹ in milk, and from 1.2 to 32.0 µg kg⁻¹ in infant formulas and whole powdered milks. The androstenedione concentrations varied from 0.39 to 0.79 µg l⁻¹ in milks, and from 0.29 to 1.2 µg kg⁻¹ in infant formulas and whole powdered milks. Two post-target compounds, one isomer of oestriol and 5α-dihydroprogesterone, were tentatively identified by post-target analysis in two of 11 real samples.

Keywords:

• oestrogens
• progestogens
• androgens
• phenols
• screening
• ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry
• dansylation
• powdered milk
• milk

Acknowledgements

The authors gratefully appreciate the National Key Technology R&D Program in the Eleven Five-Year Plan of the People's Republic of China (Project References 2006BAI19B02 and 2008ZX07421-004) and the Young Foundation of Fudan University, China (Number EYF 201023).