Sz. Li et al., CONFIRMATION OF OCHRATOXINS IN BIOLOGICAL SAMPLES BY CONVERSION INTO METHYL-ESTERS IN ACIDIFIED METHANOL, Journal of agricultural and food chemistry, 46(10), 1998, pp. 4307-4312
There is need to confirm the presence of ochratoxin A (OA) and its met
abolites in biological samples following chromatographic analysis. One
method is to convert the ochratoxins into different forms. A simplifi
ed procedure has been developed for the esterification of OA, GB (dech
lorinated GA), O alpha (hydrolyzed GA), and OA-OH (hydroxy-OA) in the
presence of methanol and HCl. The percentage conversion of GA into its
corresponding methyl ester (OA-Me) was >95% when the sample was incub
ated for a period of >12 h at 20 degrees C in the presence of 6 N or h
igher concentrations of HCl and a high relative volume of methanol (95
% v/v). Similar results were obtained with OA, OB, and GA-OH when pres
ent as pure preparations or in tissue extracts of kidney, liver, bile,
and blood. The conversion of O alpha into O alpha-Me was not quantita
tive. The detection limit of the assay for OA and OA-Me was 1 ng/mL. T
he procedure can be used for the confirmation of the ochratoxins in bi
ological samples or for the synthesis of their eaters.