Molecularly imprinted stir bars for selective extraction of thiabendazole in citrus samples

Stir-bar sorptive extraction is based on the partitioning of target analytes between the sample (mostly aqueous-based liquid samples) and a stationary phase-coated magnetic stir bar. Until now, only PDMS-coated stir bars are commercially available, restricting the range of applications to the non-selective extraction of hydrophobic compounds due to the apolar character of PDMS. In this work, a novel stir bar coated with molecularly imprinted polymer as selective extraction phase for sorptive extraction of thiabendazole (TBZ) was developed. Two different procedures, based on physical or chemical coating, were assessed for the preparation of molecularly imprinted stir bars. Under optimum conditions, recoveries achieved both in imprinted and non-imprinted polymer stir bars obtained by physical coating were very low, whereas TBZ was favourably retained by imprinted over non-imprinted polymer stir bars obtained by chemical coating and thus the latter approach was used in further studies. Different parameters affecting both stir-bars preparation (i.e. cross-linker, porogen, polymerization time) and the subsequent selective extraction of TBZ (i.e. washing, loading and elution solvents, extraction time) were properly optimized. The molecularly imprinted coated stir bars were applied to the extraction of TBZ from citrus samples (orange, lemon and citrus juices) allowing its final determination at concentrations levels according to current regulations.