Stoichiometric molecular imprinting using polymerisable urea and squaramide receptors for the solid phase extraction of organo-arsenic compound roxarsone.

The design, preparation and evaluation of molecularly imprinted polymers for roxarsone (4-hydroxy-3-nitrophenylarsonic acid), an organo-arsenic swine and poultry feed additive, using bi-substituted ureas and squaramide receptors as the functional monomers, are demonstrated. Pre-polymerisation studies of the template-monomer complexation performed by 1H NMR experiments show that squaramide-based monomers provide association equilibrium constant values higher than urea-based monomers. Equilibrium rebinding experiments in methanol show that two squaramide-based materials have good molecular recognition properties towards roxarsone, with high affinity (Keq = 16.85 × 103 L mol-1 and 14.65 × 103 L mol-1, respectively), high imprinting factors (4.73 and 3.64 respectively) and good selectivity towards two roxarsone-related compounds, acetarsone (3-acetamido-4-hydroxyphenylarsonic acid) and nitarsone (4-nitrophenylarsonic acid). Polymer MIP-SQ2 was successfully used to setup an experimental protocol for the direct solid phase extraction of roxarsone from surface water samples. The method gives clean HPLC traces, with recoveries between 91% and 95% at concentration levels of 5.0, 10, and 25 mg L-1. Sample preconcentration with good recoveries between 87% and 97%, are shown, confirming that it is possible to employ the developed materials to measure roxarsone down to 1 μg L-1 in water samples.