Preparation of wax-based molecularly imprinted monolith for pipette-tip solid-phase extraction: a hybrid method

The development of molecularly imprinted monolith (MIM) for pipette-tip solid-phase extraction (PT-SPE) for sample pretreatment is challenging . In this work, a wax-based molecularly imprinted monolith (WMIM) was successfully prepared with a hybrid method by integration of the traditional packing SPE column and MIM, including preparation of the salt column inside the pipette, polymerization of wax-based imprinted column (WIC) outside the pipette, and immobilization of WIC inside the pipette tip. To ensure the penetration of samples and solvents during the PT-SPE, micrometer-range interconnected macropores were tailor-made via the salt-template sacrifice method. For the production of high affinity imprinted sites within the WIC, octadecanoic acid was used as functional monomer in the paraffin matrix. In terms of the adsorption property, the synthesized WIC exhibited a specific affinity to cardiovascular drugs, with an imprinting factor (IF) of 4.8 for the target analyte. Moreover, the WMIM-based PT-SPE was coupled with fluorescence spectrophotometry for the target propranolol determination  (the excitation and emission wavelengths were 294 nm and 343 nm, respectively). This analytical method showed high recovery of target detection in different real samples (R > 90%), good sensitivity, and accuracy (R² = 0.99, LOD = 0.03 ng mL^-1). We believe this work could provide a significant contribution  for the fabrication of MIM and promote an emerging trend of developing elution-free materials for sample pretreatment.