Molecularly Imprinted On-Line Solid-Phase Extraction Coupled with Fluorescence Detection for the Determination of Ochratoxin A in Wheat Samples

Abstract

An automatic solid-phase extraction (SPE) system coupled with a fluorescence detector was developed for the sensitive determination of Ochratoxin A (OTA) in wheat at the ng mL−1 levels. Cross-linked molecularly imprinted polymers (MIPs) were synthesized as sorbents by a non-covalent approach using N-(4-chloro-1-hydroxy-2-naphthoylamido)-(L)-phenylalanine (OTAm) as a mimic template, methacrylic acid as functional monomer, and ethylendimethacrylate as the cross-linker in chloroform porogenic solvent, polymerizing the mixture by thermal treatment at 60°C. These MIP polymers showed excellent affinity and specificity in the recognition of natural OTA mycotoxin compared to the results obtained with nonimprinted polymers. The polymers were slurry packed into a SPE column (V∼1.7 mL) and used in a SPE flowing system coupled to on-line molecular fluorescence detection (named MISPE-FLD) for the OTA determination. Methanol (MeOH), MeOH:H2O (1:9) + 1% acetic acid (AcOH), and MeOH:tributylamine (99:1) were tested as desorbing solvents. A dynamic binding capacity of 118 ± 9 ng of OTA (n = 3) was calculated for 45 mg of dry MIP particles. The described instrument demonstrated the cleanup of the matrix by the imprinted column and the simultaneous determination of OTA in wheat samples in the range 3–18 ng mL−1(LOD 1.2 ng mL−1 of OTA). The recoveries of reference wheat flour materials spiked with OTA were about 93 ± 9%. The MISPE-FLD instrument can be used for concentrations below the maximum levels of the EC regulatory limits for OTA in unprocessed cereals (5.0 µg kg−1) (EC Commission Regulation 2006).