Comparative study of an estradiol enzyme-linked immunosorbent assay kit, liquid chromatography–tandem mass spectrometry, and ultra performance liquid chromatography–quadrupole time of flight mass spectrometry for part-per-trillion analysis of estrogens in water samples

Abstract

Estrogens have been often identified as the major contributors to the endocrine-disrupting activity observed in environmental waters. However, their analysis in these, sometimes very complex, matrices is still challenging due to the very low detection limits and the selectivity required for their reliable determination at the very low concentrations at which they are physiologically active. In this work, a polyclonal enzyme-linked immunosorbent assay (ELISA) kit for 17-β-estradiol analysis, high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) based on triple-quadrupole analyzer (QqQ), and a newly developed method based on ultra performance liquid chromatography–quadrupole time of flight mass spectrometry (UPLC–Q-TOF-MS) have been evaluated in terms of performance for the rapid screening, quantitative analysis, and unequivocal identification of some selected, environmentally relevant estrogens in different water matrices, including urban wastewater, river water, and ground water, after solid phase extraction. Compounds quantified and/or identified included the estrogens 17-β-estradiol, estrone, 17-α-ethynyl estradiol and estriol, and the isoflavones daidzein, genistein, and biochanin A. Except for a moderate overestimation using the ELISA kit, especially in the analysis of complex wastewater samples, results obtained by all the investigated techniques were in very good, general agreement. The instrumental sensitivity achieved increased in the order: UPLC–Q-TOF-MS < polyclonal ELISA kit < HPLC–MS/MS (QqQ). Direct analysis of water samples by using the ELISA kit permitted to reach a limit of detection of 2.5 ng L −1. However, using an appropriated sample pretreatment method detection limits at nanogram to picogram per liter levels can be obtained with all techniques and the risk for matrix effects is minimized. In terms of selectivity, both HPLC–MS/MS (QqQ) and UPLC–Q-TOF-MS show outstanding performance, but the latter allows, in addition, shorter analysis times (16 min vs. 45 min) and the identification of non-target, unknown compounds. The identification of unknown compounds is based on the accurate mass measurements for the precursor and product ions, that permit the elemental compositions calculation and the chemical structures to be identified searching against different databases.