Preparation, characterization and application of organic–inorganic hybrid caffeine imprinted monolith

• An organic–inorganic hybrid caffeine imprinted monolith was synthesized.
• The synthesis conditions and the morphology of the monolith were studied.
• The monolith was applied as the adsorbent for the extraction of caffeine in milk.
• A method for the determination of caffeine in children's milk was developed.

The present work aims to synthesize an organic–inorganic hybrid caffeine imprinted monolith using one-step method. The synthesis conditions such as the type of inorganic precursor and porogenic solvent, the molar ratios of the monomer and cross-linker, the volume ratio of the inorganic alcoholysate and organic part were optimized. The morphology of the monolith was studied by scanning electron microscopy and Fourier transform infrared spectra. The imprinted factor of the monolith for caffeine reached 3.02. A simple, rapid and sensitive method for the determination of caffeine in children's milk using the organic–inorganic hybrid caffeine imprinted polymer monolith microextraction combined with high-performance liquid chromatography-photodiodes array detector was developed. Several parameters affecting the sample pretreatment were investigated, including the type, flow rate and volume of eluent, the flow rate and volume of sample solution. The assay exhibited a linear dynamic range of 8–500 μg L−1 with the correlation coefficient above 0.9987. Lower limits of detection (LOD, at S/N = 3) and quantification (LOQ, at S/N = 10) in children's milk samples were 2.7 and 8 μg L−1. Recoveries of caffeine from spiked children's milk ranged from 85 to 104% with relative standard deviations of less than 8.9%.