Surface reversible addition-fragmentation chain transfer (RAFT) polymerization method was firstly applied to the preparation of molecularly imprinted polymer (MIP) coated silicon solid-phase microextraction (SPME) fibers. With Sudan I as template, an ultra-thin MIP coating with about 0.55-μm thickness was obtained with homogeneous structure and controlled composition, due to the controllable radical growing and chain propagation in surface RAFT polymerization. The MIP-coated fibers were found with enhanced selectivity coefficients (3.0–6.5) to Sudan I–IV dyes in contrast with those reported in our previous work. Furthermore, the ultra-thin thickness of MIP coating was helpful to the effective elution of template and fast adsorption/desorption kinetics, so only about 18 min was needed for MIP-coated SPME operation. The detection limits of 21–55 ng L−1 were achieved for four Sudan dyes, when MIP-coated SPME was coupled with liquid chromatography (LC) and mass spectrometry (MS) detection. The MIP-coated SPME–LC–MS/MS method was tested for the monitoring of ultra trace Sudan dyes in spiked chilli tomato sauce and chilli pepper samples, and high enrichment effect, remarkable matrix peaks-removing capability, and consequent high sensitivities were achieved to four Sudan dyes.Graphical abstractHighlights► Surface RAFT polymerization was firstly applied to MIP-coated fiber preparation. ► Ultra-thin MIP coating of about 0.55 μm was obtained with homogenous structure. ► MIP-coated fiber showed improved selectivities to Sudan I–IV dyes. ► MIP-coated SPME–LC–MS/MS method was used for monitoring of trace Sudan dyes.

In this research, a novel strategy was developed to prepare molecularly imprinted polymer (MIP) coated solid-phase microextraction fibers on a large scale with Sudan I as template and stainless steel fibers as substrate. More than 20 fibers could be obtained in one glass tube, and the efficiency and coating repeatability were enhanced remarkably in contrast with the yield of only one fiber in our previous works. The obtained MIP-coated stainless steel fibers were characterized by homogeneous and highly cross-linked coating, good chemical and thermal stabilities, high extraction capacities, and specific selectivities to Sudan I–IV dyes. Based on the systemic optimization of extraction conditions, a simple and cost-effective method based on the coupling of MIP-coated SPME with high-performance liquid chromatography was developed for the fast and selective determination of trace Sudan I–IV dyes in hot chili powder and poultry feed samples. The limits of detection of Sudan I–IV dyes were within 2.5–4.6 ng g−1, and the spiked recoveries were in the range of 86.3–96.3% for hot chili powder sample and 84.6–97.4% for poultry feed sample.Highlights► Novel strategy was developed to prepare MIP-coated SPME fibers on a large scale. ► More than 20 fibers could be obtained in one glass tube. ► MIP-coated fibers show high selectivities and extraction capacities to Sudan dyes. ► MIP-coated SPME–HPLC–UV method was developed for trace analysis of Sudan dyes.

A novel liquid–liquid–solid microextraction (LLSME) method was developed to overcome the well-known water-compatibility problem of molecularly imprinted polymers (MIPs). The enrichment factors with MIP-LLSME method were within 70–210 for trace chloroacetanilide herbicides under optimized extraction conditions. The method was characterized by simplicity, low solvent-consumption and high selectivity, and it was suitable for the one-step pretreatment of various aqueous samples such as river water and farm water.

A molecularly imprinted polymer (MIP) with metolachlor as template was firstly coated on stainless steel fiber through chemical bonding strategy to solve the fragility problem of silica fiber substrate for solid-phase microextraction. The surface pretreatment of stainless steel fiber and the polymerization conditions were investigated systematically to enhance the preparation feasibility and MIP coating performance, and then a porous and highly cross-linked MIP coating with 14.8-μm thickness was obtained with over 200 times re-usability which was supported by non-fragile stainless steel fiber adoption. The MIP coating possessed specific selectivities to metolachlor, its metabolites and other chloroacetanilide herbicides with the factors of 1.1–4.6. Good extraction capacities of metolachlor, propisochlor and butachlor were found with MIP coating under quick adsorption and desorption kinetics, and the detection limits of 3.0, 9.6 and 38 μg L−1 were achieved, respectively. Moreover, the MIP-coated stainless steel fiber was evaluated for trace metolachlor, propisochlor and butachlor extraction in the spiked soybean and corn samples, and the enrichment factors of 54–60, 27–31 and 15–20 were obtained, respectively.