Comparison of normal and reversed-phase solid phase extraction methods for extraction of beta-blockers from plasma using molecularly imprinted polymers

A molecularly imprinted polymer (MIP) prepared using propranolol as template, methacrylic acid (MA) and ethylene glycol dimethacrylate (EGDMA) was used to develop SPE methods in "reversed-" and normal phase mode for an analogue of propranolol (M47070) with another analogue (M45655) used as an internal standard. The compounds were also extracted in reversed-phase mode onto a non-imprinted polymer. It was necessary to employ a protein precipitation step ahead of MIP-SPE in order to facilitate downstream analysis. High extraction efficiencies and linear calibration ranges were achieved using both reversed-phase (RP) and normal phase (NP) MIP-based methods. Extraction efficiencies were lower on the non-imprinted polymer indicating stronger retention by the MIP. This stronger retention was attributed to selective imprint-based binding by the MIP that was not available for the non-imprinted polymer. Although clean extracts were obtained in both RP and NP modes, low level interference from template-related impurities or degradation products compromised detection of M47070 at low concentrations for the MIP-based methods. This interference made accuracy of the MIP-based methods poorer at low concentrations. The reversed-phase method showed marginally better accuracy and precision than the normal phase method.