Determination of ochratoxin A in red wines by multiple pulsed elutions from molecularly imprinted polypyrrole

Carbon nanotubes (CNTs) were used successfully to enhance the binding capacity of a molecularly imprinted polypyrrole (MIPPy)-modified stainless steel frit for micro-solid phase extraction (μSPE). Low back pressure of this new MIPPy/CNTs-modified stainless steel frit device made it feasible for sample preconcentration by using a syringe pump. For a 3-mL sample of red wine, preconcentration of ochratoxin A (OTA) was achieved within 6 min at a flow rate of 0.5 mL/min. In order to eliminate matrix interferences, two new approaches based on differential or multiple pulsed elution (PE) were developed for the determination of OTA in French (1999), Canadian (2003) and Bulgarian (2004) red wines. Elution of OTA from MIPPy/CNTs, for on-line coupling to high performance liquid chromatography (HPLC) analysis with fluorescence detection (FLD), was achieved by an ion-pairing mechanism. It was found that the % triethylamine (TEA) in the PE solution had a scalable effect on the OTA retention time, as influenced by the formation of three different ion-pairs: [NH4+–OTA2-–NH4+], [NH4+–OTA2-–TEA+], and [TEA+–OTA2-–TEA+TEA+–OTA2-–TEA+]. Preliminary method validation showed that the Bulgarian red wine was best analyzed by MIPPy/CNTs–μSPP–PE–HPLC–FLD using 2% TEA. The reproducibility was 8.9% RSD and the limit of detection was 0.08 ppb (S/N = 3), which is more than adequate for handling the regulatory level of 2 ppb.