Molecularly imprinted nanoparticles grafted to porous silica as chiral selectors in liquid chromatography

- Imprinted nanoparticles are presented as efficient chiral selectors.
- Nanoparticles were covalently immobilised on porous silica supports.
- Both precipitation polymerisation and solid-phase synthesis were explored.
- The developed stationary phase successfully resolved the racemate of citalopram.
- S-citalopram and its major metabolites were separated and quantified in urine.

The work presented here explores the grafting of molecularly imprinted nanoparticles (MIN) on silica beads for the development of new chiral stationary phases (CSP). Both solid-phase imprinting and precipitation polymerisation were tested for MIN synthesis though the latter approach was the only one that provided efficient chiral selectors. MIN particles were prepared by iniferter polymerisation initiated by UV radiation, using itaconic acid as functional monomer and ethylene dimethacrylate as cross-linker. This resulted in particles with an average size of 249.0 ± 4.0 nm which were covalently immobilised onto chromatographic silica beads. The resultant CSP based on the composite silica beads-MIN was capable of resolving the racemate of the antidepressant drug citalopram and also separating its major metabolites by liquid chromatography, with better efficiency and peak symmetry than other MIP based CSP. The methodology presented here allowed for the quantification of the pharmacologically active enantiomer (+)-(S)-citalopram (SCIT) and its main metabolites (+)-(S)-desmethylcitalopram (SDCIT) and (+)-(S)-didesmethylcitalopram (SDDCIT) in urine, registering mean recoveries that ranged from 91.5 to 103.7% with RSD values that were below 10% in all tested concentration levels (0.1, 0.75 and 5 μg mL−1), which confirmed method suitability for the intended application.