Preparation of a new restricted access molecularly imprinted hybrid adsorbent for the extraction of folic acid from milk powder samples

Abstract

A new hybrid molecularly imprinted polymer (MIP) combined with restricted access (RAM) has been synthesized based on random free-radical polymerization and a sol–gel process. From competitive adsorption studies by using the RAM-MIP and RAM-NIP with folic acid and structurally similar molecules (caffeine, 4-aminobenzamide or paracetamol), relative selectivity coefficients (k) higher than one unit were achieved, indicating good recognition selectivity for folic acid. The percentage of BSA protein exclusion was higher for the RAM-MIP (55.3 ± 2.0) as compared to the MIP (35.9 ± 2.5%). The solid phase extraction (SPE) procedure was performed by loading the acid extract from milk powder samples previously submitted to saponification and acidification with 10% trichloroacetic acid (TCA) until pH 1.5, through 100 mg of RAM-MIP packed into SPE cartridge. The elution step was carried out by using a mixture of acetonitrile : 0.266 mol L⁻¹ acetate buffer at pH 5.7 (15 : 85, v/v), the same composition of the mobile phase of HPLC. The intra-day precision (n = 10) of the procedure assessed as relative standard deviation (RSD) was 4.7 and 4.1% for the respective concentrations of 20.0 and 150.0 μg L⁻¹. The applicability of the method was attested by analysis of different brands of milk powder samples fortified with folic acid, as well as by high recovery percentages 95.0–108.4% obtained upon addition and recovery tests. The cleanup process accomplished by RAM-MIP was so efficient that very few remaining matrix components were detected in the eluate by high performance liquid chromatography.