Jacket-free stir bar sorptive extraction with bio-inspired polydopamine-functionalized immobilization of cross-linked polymer on stainless steel wire

• Stainless steel needles with chemical resistance are used for jacket-free stir bar sorptive extraction.
• Mussel-inspired polydopamine functionalization for chemical modification on stainless steel needle.
• Modified monolith shows high selectivity for selective extraction of protoberberines.
• Great potential application in pharmaceutical analysis and pharmacokinetics study.

Stainless steel wire (SSW) is a good substrate for stir bar sorptive extraction (SBSE). However, it is still a challenge to immobilize commonly used cross-linked polymers onto SSW. In this work, we present a new approach for immobilization of the cross-linked organic polymer onto SSW for jacket-free SBSE. A dopamine derivative was firstly synthesized; by introducing a mussel-inspired polydopamine process, a stable coating layer was finally generated on the surface of SSW. Secondly, the cross-linked polymer was synthesized on the polydopamine-modified SSW by using acetonitrile as the porogen, acrylamide (AA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker and 2,2′-azobis (2-methylpropionitrile) as the initiator. A diluted pre-polymerization solution was carefully prepared to generate a thin layer of the polymer. The prepared poly(EGDMA-AA)-modified stir bar showed high stability and good tolerance toward stirring, ultrasonication, organic solvents, and strong acidic and basic conditions. Morphology and structure characterization of coatings were performed by scanning electron microscopy and Fourier transform infrared spectra, respectively. The prepared poly(EGDMA-AA)-modified stir bar showed great extraction efficiency toward protoberberines, with enrichment factors of 19–42. An SBSE-HPLC method was also developed for quantitative analysis of protoberberines. The method showed low limits of detection (0.06–0.15 ng mL−1), wide linear range (0.5–400 ng mL−1), good linearity (R ≥ 0.9980) and good reproducibility (RSD ≤ 3.60% for intra-day, RSD ≤ 4.73% for inter-day). The developed method has been successfully applied to determine protoberberines in herb and rat plasma samples, with recoveries of 88.53–114.61%.