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Twenty-five samples of retail corn flakes (from 15 lots) were analysed for fumonisin B(1) (FB(1)) and fumonisin B(2) (FB(2)). They were detected in 22 and 12 samples, respectively, at respective mean concentrations 68 and 8 ng g(-1). Samples were extracted with methanol-acetonitrile-water (25:25:50) and there was an excellent correlation for FB(1) between results obtained with C(18) clean-up and those obtained with the immunoaffinity column (IAC) clean-up. After extraction of the corn flakes' residue with 1% sodium dodecyl sulphate (SDS) solution and hydrolysis with 2 N potassium hydroxide, hidden (protein bound) fumonisin was determined as HFB(1), which was found in residues from all the corn flakes samples, even those containing no detectable FB(1); the average concentration of HFB(1) was 101 ng g(-1), equivalent to 180 ng FB(1) g(-1). Thus, our results showed an average of 2.6 times more FB(1) present in bound form as was determined by conventional analysis. We found a correlation coefficient of -0.5034 for a logarithmic relationship between the FB(1) (C(18) clean-up) and HFB(1) concentrations The highest concentration of HFB(1) formed was 288 ng g(-1) from a sample containing only 12-15 ng FB(1) g(-1), while the lowest concentration of HFB(1) was 26 ng g(-1) from a sample with 152-155 ng FB(1) g(-1). This low degree of correlation should be taken into account by food safety authorities in estimates of human exposure to protein bound fumonisin.

Blood plasma samples collected from 144 healthy volunteers in 16 locations across Canada in 1994 were analysed for ochratoxin A (OTA). The method of analysis included cleanup by C18 solid phase extraction and immunoaffinity columns followed by liquid chromatography (LC) with fluorescence detection, which gave 86.5% (s.d. = 9.7) recovery (n = 31) of OTA (added at 2 ng/ml) with a detection limit of 0.15 ng/ml. The arithmetic mean concentration found in the plasma samples, corrected for volume of anticoagulant added, was 0.88 ng/ml with a standard deviation of 0.35 ng/ml and a range of 0.29-2.37 ng/ml. Confirmation of identity of OTA was by methyl ester formation for 65 samples and by LC-tandem mass spectrometry for 17 samples (some of which were included in pooled samples). Statistical analysis, by ANOVA of the log OTA plasma concentrations, showed a highly significant effect due to location in Canada (p = < 0.0001) but no effect due to age, sex or blood group of donors. The highest mean concentration was found in Winnipeg, significantly different (p = 0.05) by the Student-Newman-Keuls multiple range test from the lowest levels found in Toronto, Vancouver and Saint John.