Synthesis of novel magnetic CoFe2O4-embedded MIL-101 with tetramethylammonium hydroxide for extraction of toxic flame retardants in environmental water samples

Novel magnetic CoFe2O4-embedded MIL-101(Cr) with tetramethylammonium hydroxide (CoFe2O4/MIL-101T) was prepared through the facile hydrothermal method. Tetramethylammonium hydroxide acts as a template molecule and avoids the recrystallisation of terephthalic acid. The material was applied as the adsorbent in the magnetic solid-phase extraction (MSPE) process coupled with high-performance liquid chromatography to detect the five flame retardants in environmental water samples. Several parameters affecting MSPE efficiency were systematically investigated, such as MIL-101T content, material amount, desorption solvents, adsorption time, solution pH, theoretical maximum enrichment factor (EFmax) and the reusability. Under optimised conditions, good linearities were achieved for five flame retardants with correlation coefficients R2 > 0.9961. The limits of detections for analytes at the signal-to-noise ratio of three were 0.013–0.071 μg·L−1. This method was applied to the analysis of tap, pond, lake and river waters. The recoveries were in the range of 81.5 ± 3.2–107.0 ± 2.3% with the relative standard deviations ranging from 0.11% to 8.66% in four real water samples. The adsorption mechanism was the hydrophobic interaction between the material and the analytes besides pore adsorption action of the material.