Comparison study of nanofibers, composite nano/microfiber materials, molecularly imprinted polymers, and core-shell sorbents used for on-line extraction-liquid chromatography of ochratoxins in Tokaj wines

On-line solid phase extraction coupled with liquid chromatography enables high sample throughput, pre-concentration of analytes, efficient clean-up, and separation in a single step. Our comparison study focused on the selection of an optimal SPE sorbent for on-line extraction of ochratoxins A and B allowing fast and sensitive control of mycotoxin contamination. Four types of fibrous sorbents including polyethylene microfibers, polypropylene microfibers, polycaprolactone microfibers/nanofibers composite, and polycaprolactone microfibers/ polyvinylidene difluoride nanofibers composite together with selective molecularly imprinted polymers, and conventional C18 core-shell particle sorbent were tested, and efficiency of extraction was compared in on-line mode. Clean-up efficiency and ability to remove matrix interferences with the subsequent chromatographic separation were optimized for all extraction materials followed by validation of the methods. Both nanofibers and molecularly imprinted polymer sorbents were packed in a stainless-steel cartridge and directly connected to the HPLC system. Only polyethylene microfibers among all the tested fibers achieved the selectivity desired for resolution of ochratoxins from the wine matrix with the validation parameters comparable to commercial C18 sorbent. The best results featuring a limit of detection 0.03-0.06 mu g L-1, recoveries 92-97% with RSD < 2%, and only 6 min overall analysis time were obtained after extraction using C18 particles. Features including stability of fibers in organic solvents, under high pressure, and their multiple reusability were also proven. Comparison of several types of extraction sorbents for ochratoxins was demonstrated with their on-line extraction followed by liquid chromatography with fluorescence determination using Tokaj wine as a complex matrix.