Quantification of ochratoxin A in foods by a stable isotope dilution assay using high-performance liquid chromatography-tandem mass spectrometry.
A stable isotope dilution assay (SIDA) was developed for quantification of the mycotoxin ochratoxin A (OTA) by using [2H5]-OTA as internal standard. The synthesis of labelled OTA was accomplished by acid hydrolysis of unlabelled OTA and subsequent coupling one of the products, ochratoxin alpha, to [2H5]-L-phenylalanine. The mycotoxin was quantified in foods by LC-tandem MS after extraction with buffers containing [2H5]-OTA and clean-up by immuno affinity chromatography or by solid phase extraction on silica. The method showed a sufficient sensitivity with a low detection and quantification limit of 0.5 and 1.4 microg/kg, respectively, and good precision in inter-assay studies showing a CV (n = 3) of 3.6%. The analysis of certified reference materials resulted in a low bias of 2.1% from the certified values and revealed excellent accuracy of the new method. To prove the suitability of SIDA. OTA was quantified in a number of food samples and resulted mainly in not detectable OTA contents. However, three samples of raisins exceeded the legal limit of 10 microg/kg and highlighted the need for further controlling the contamination with the mycotoxin.
Lindenmeier
Michael
M
Institut für Lebensmittelchemie der Technischen Universität München, Lichtenbergstr. 4, D-85748 Garching, Germany.
Schieberle
Peter
P
Rychlik
Michael
M
D002138:Calibration; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D005504:Food Analysis; D009183:Mycotoxins / Q000032:analysis*; D009793:Ochratoxins / Q000032:analysis*; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
D009183:Mycotoxins; D009793:Ochratoxins; C025589:ochratoxin A