Development and validation of methods using solid-phase extraction, offline derivatization and UHPLC-ESI(+)-MS/MS for the quantification of estrogenic compounds at ultra-trace levels in different types of water

Natural estrogens (estrone: E1, 17-β-estradiol: E2, estriol: E3) and synthetic estrogen (17-α-ethinylestradiol: EE2) belong to the group of endocrine disrupting compounds (EDCs), leading to deleterious effects on aquatic biota, even at sub-ng/L level of concentration. The European Union (EU) published a Watch-List of substances including these estrogenic compounds and specified maximum acceptable method detection limits (LODs) of 0.035 ng/L for EE2 and 0.4 ng/L for E1 and E2. Besides, E2 will have to be monitored as an indicator of the occurrence of EDCs in water intended for human consumption, with a parametric value of 1 ng/L (EU 2020/2184). Attaining these limits represents a challenge even with the most up-to-date analytical tools, particularly in surface water. Initially, an automated solid-phase extraction (SPE) method using a single cartridge with hydrophilic-lipophilic balanced copolymer was developed and validated. This method is suitable for clean aqueous matrices (drinking water) and allows for high sample throughput. However, for more complex matrices such as surface water/effluent of wastewater treatment plant, an additional purification step was necessary. After a careful optimization of the sample preparation parameters to maximize the recoveries, the extraction of a whole water sample on a SPE disk, followed by purification on a Florisil SPE cartridge, allowed to reach the sensitivity required by the EU Watch-List. The final optimized method was validated (precision and trueness) in seven surface water from different Belgium locations.