β-Ketoenamine-linked covalent organic framework absorbent for online micro-solid phase extraction of trace levels...

Covalent organic frameworks with tunable porous crystallinity and outstanding stability have exhibited fascinating pretreatment performance as ideal extraction media. Herein, the β-ketoenamine-linked TpPa-1 synthesized by 1,3,5-triformylphloroglucinol and paraphenylenediamine was employed as the absorbent for online micro-solid phase extraction of trace bisphenols combined with high-performance liquid chromatography detection. A series of characterizations indicated that the TpPa-1 possessed large surface areas, high stability, and hydrophobicity. The main experimental parameters affecting the extraction efficiency were optimized in detail. Compared with four commercial sorbents, the TpPa-1 exhibited superior enrichment capacity for extracting bisphenols. Under the optimum conditions, the established method demonstrated a wide linear range and high sensitivity with the limit of detection ranging from 0.05-0.06 μg/L. Furthermore, the developed method was successfully applied to determine bisphenols in plastic samples. Bisphenol A was actually detected in a transparent box with a concentration of 0.31 μg/g, and the recoveries of the four bisphenols in the plastic samples were 80.5-116% with the relative standard deviation less than 9.2%. Such performance was attributed to recognition affinity, including the π-π affinity, hydrophobic effect, and hydrogen bond. These results demonstrated that TpPa-1 possessed great potential to be an excellent pretreatment medium for online separation and analysis of trace analytes in complex samples.