Synthesis and evaluation of new propazine-imprinted polymer formats for use as stationary phases in liquid chromatography

Silica particles have been used as supports for the preparation of three different propazine-imprinted polymer formats. First format refers to grafting of thin films of molecularly imprinted polymers (MIPs) using an immobilised iniferter-type initiator (inif-MIP). The other two new formats were obtained by complete filling of the silica pores with the appropriate polymerisation mixture leading to a silica-MIP composite material (c-MIP) followed by the dissolution of the silica matrix resulting in spherical MIP beads (dis-MIP). These techniques offer a mean of fine-tuning the particle morphology of the resulting MIP particles leading to enhanced capacity in chromatographic applications. Porous silica (specific surface area S = 380 m² g⁻¹, particle size p_s = 10 μm, pore volume V_p = 1.083 ml g⁻¹ and pore diameter d_p = 10.5 nm), methacrylic acid and ethylenglycol dimethacrylate were used for the preparation of the materials. All the MIP formats imprinted with propazine have been characterised by elemental analysis, FT-IR spectroscopy, nitrogen adsorption and scanning electron microscopy. Further, the materials were assessed as stationary phases in HPLC. Capacity factors, imprinting factors and theoretical plate numbers were calculated for propazine and other related triazines in order to compare the chromatographic properties of the three different stationary phases. For the inif-MIPs the column efficiency depended strongly on the amount of grafted polymer. Thus, only the polymers grafted as thin films of ca. 1.3 nm average thickness show imprinting effects and the highest column efficiency giving plate numbers (N) of 1600 m⁻¹ for the imprinted propazine. The performance of the c-MIP stationary phase decreases as result of the complete pore filling after polymerisation and increases again after the removal of the silica matrix due to a better mass transfer in the porous mirror-image resulting polymer. From this study can be concluded that the inif-MIP shows the best efficiency for use as stationary phase in HPLC for the separation of triazinic herbicides.