Simplified miniaturized analytical set-up based on molecularly imprinted polymer directly coupled to UV detection for the determination of benzoylecgonine in urine

A simple, selective, and sensitive method involving a miniaturized solid phase extraction step based on a monolithic molecularly imprinted polymer (MIP) directly coupled on-line to UV detection was developed for the determination of benzoylecgonine (BZE) in complex biological samples. Monolithic MIPs were prepared into 100 mu m internal diameter fused-silica capillaries either by thermal or photopolymerization. While leading to similar selectivities with respect to BZE, photopolymerization has made it possible to produce monoliths of different lengths that can be adapted to the targeted miniaturized application. The homogeneous morphology of these monolithic MIPs was evaluated by scanning electron microscopy prior to measuring their permeability. Their selectivity was evaluated leading to imprinting factors of 2.7 +/- 0.1 for BZE and 4.0 +/- 0.6 for cocaine (selected as template for the MIP synthesis) with polymers resulting from three independent syntheses, showing both the high selectivity of the MIPs and the reproducibility of their synthesis. After selecting the appropriate capillary length and the set-up configuration and optimizing the extraction protocol to promote selectivity, the extraction of BZE present in human urine samples spiked at 150, 250, and 500 ng mL(-1) was successfully carried out on the monolithic MIP and coupled directly on-line with UV detection. The very clean-baseline of the resulting chromatograms revealing only the peak of interest for BZE illustrated the high selectivity brought by the monolithic MIP. Limits of detection and quantification of 56.4 ng mL(-1) and 188.0 ng mL(-1) were achieved in urine samples, respectively. It is therefore possible to achieve analytical threshold in accordance with the legislation on BZE detection in urine without the need for an additional chromatographic separation.

Automated summary

A simple, selective, and sensitive method for determining benzoylecgonine in complex biological samples was developed, utilizing a miniaturized solid phase extraction step with a monolithic molecularly imprinted polymer directly coupled to UV detection. The method achieved high selectivity and reproducibility, with limits of detection and quantification meeting regulatory standards for BZE detection in urine without the need for additional chromatographic separation. The photopolymerization technique allowed for the production of monoliths of varying lengths to adapt to different applications.