Covalent immobilization of ionic liquid-based porous polymer onto poly(ether ether ketone) for stir bar sorptive extraction and its application in analysis of chlorophenoxy acid herbicides in soil

The application of stir bar sorptive extraction (SBSE) for polar compounds has been restricted because of less choice of suitable sorbents. In this study, an ionic liquid-based organic polymer with desired anionic exchange ability and porous structure was used for extraction of polar analytes with high extraction efficiency and capacity. For improving the workability of stir bar, the polymer was immobilized onto chemically resistant poly(ether ether ketone) (PEEK) tube by covalent modification method which including a skillful functionalization process. Afterwards, a facile detachable dumbbell-shaped structure with modified PEEK tube as jacket was constructed. Due to the excellent chemical and physical strength of PEEK material and dumbbell-shaped structure, the stir bar performed remarkable stability in the SBSE process. In addition, the detachable structure allowed the elution can be accomplished directly in the insert tube of autosampler vial with small amounts of solution, which significantly enhanced the enrichment factor and simplified the operation. After coupling with HPLC-MS/MS, the prepared organic polymer modified stir bar was applied for the analysis of three chlorophenoxy acid herbicides and showed favorable extraction efficiency with enrichment factors between 198 and 206 folds. For quantitative analysis of three chlorophenoxy acid herbicides, the method has wide linear range (0.003–10 ng/mL), good linearity (R2 ≥ 0.9958) and good reproducibility (intra-day relative standard deviation ≤ 6.16%). Furthermore, the proposed method was applied to determine chlorophenoxy acid herbicides in soil samples, the recoveries ranged from 79.4% to 97.4%, with relative standard deviation ≤ 9.3%.