Direct monitoring of ochratoxin A in cheese with solid-phase microextraction coupled to liquid chromatography-tandem mass spectrometry

An in situ application of solid-phase microextraction (SPME) as a sampling and sample preparation method coupled to HPLC-MS/MS for direct monitoring of ochratoxin A (OTA) distribution at different locations in a single cheese piece is proposed to be suited to the acidic analyte the extraction phase (carbon-tape SPME fiber) was acidified With aqueous solution Of HCl at pH 2. instead of the traditional sample pre-treatment with acids before SPME sampling For calibration, kinetic on-fiber-standardization Was used. which allowed the use of short sampling time (20 min) and accurate (quantification of the OTA in the semi-solid cheese sample. In addition. the traditional kinetic calibration that Used deuterated compounds as standards was extended to we a non-deuterated analogue ochraroxin B (OTB) as the standard of the analyte OTA, which Was supported by both theoretical discussion and experimental verification Finally. the minaturized SPMF fiber was adopted so that the concentration distribution of OTA in a small-sized cheese piece Could he directly probed The detection limit of the resulting SPME method in semi-solid gel was 15 ng/mL and the linear range was 35-500 ng/mL. The SPME-LC-MS/MS method showed good precision(RSI) similar to 10%) and accuracy (relative recovery. 93%) in the gel model. The direct cheese analysis showed comparable accuracy and precision to the established liquid extraction. As a result, the developed in mu SPME-LC-MS/MS method was sensitive. simple, accurate and applicable for the analysis of complicated lipid-rich samples such as cheese. (C) 2009 Elsevier B.V. All rights reserved