Comparison of nanofibers, microfibers, nano/microfiber graphene doped composites, molecularly imprinted polymers, and restricted access materials for on-line extraction and chromatographic determination of citrinin, zearalenone, and ochratoxin A in plant-based milk beverages

Several advanced sorbents for on-line extraction followed by chromatographic determination of citrinin, zearalenone, and ochratoxin A in a complex matrix of plant-based beverages from oat and rice milk have been compared. Twelve types of the fibrous sorbents, including polyethylene and polypropylene microfibers, polycaprolactone microfibers/polyvinylidene difluoride nanofibers composite, poly(3-hydroxybutyrate) microfibers, poly(3-hydroxybutyrate) microfibers/polypropylene microfibers composite, polycaprolactone nanofibers, polycaprolactone nanofibers doped with 7.7, 20.2, and 30.7% graphene, polyacrylonitrile nanofibers, polyurethane nanofibers, and polyamide 6 nanofibers were compared in terms of extraction recovery and cleanup efficiency with both the commercial restricted access media sorbent RP-18 ADS (RAM) and molecularly imprinted polymers (MIP). The MIP sorbent was a mixture prepared from commercial Affinimip selective for ochratoxin A and zearalenone, and home-made MIP for citrinin (1:1:1). The polymer fibers and the MIP mixture were filled in a cartridge similar in size to the commercial RAM column and the clean-up step as well as the subsequent chromatographic separation were optimized. The HPLC separation of mycotoxins was carried out using Kinetex Biphenyl (150 × 4.6 mm, core–shell particle size 5 µm) analytical column followed by fluorescence detection. The excitation and emission wavelengths were set at 335/497 nm for citrinin and ochratoxin A, and 270/458 nm for zearalenone, respectively. The mobile phase used for the gradient elution of the mycotoxins consisted of 0.5% aqueous formic acid and acetonitrile. The zearalenone contaminations found in plant-based beverages ranged from 9.5 to 14.6 μg L−1 and were within the tolerable limit defined by the European Union.