A collaborative study of an HPLC method for determination of ochratoxin A in wheat using immunoaffinity column clean-up.

Thirteen laboratories within the United Kingdom participated in a collaborative study to determine ochratoxin A in wheat using an HPLC method incorporating immunoaffinity column clean-up. Mean recovery of ochratoxin A from wheat spiked at a level of 5 micrograms/kg was 91% for the method when using the OchraTest and 93% for the OCHRAPREP brands of column. Four samples naturally contaminated with ochratoxin A consisting of two blind duplicates containing concentrations of approximately 3 and 6 micrograms/kg of ochratoxin A were examined using a specified method. The relative standard deviations obtained within laboratories (repeatability) ranged between 9.7 and 12.5%, there being no significant difference between the two brands of immunoaffinity column. The relative standard deviations obtained between laboratories (reproducibility) were larger, ranging from 24.6 to 32.1% when using the OchraTest column and 14.0 and 19.6% for the OCHRAPREP column. When results were corrected for recovery, the apparent difference in reproducibility between the two columns was much reduced, 14.0-17.3% for OchraTest and 10.4-17.5% for OCHRAPREP. Horrat values for reproducibility were between 0.4 and 0.7 before correcting results for recovery and were between 0.3 and 0.6 after correction. The performance of the immunoaffinity column method tested compared very favourably with results of other published collaborative studies on mycotoxins.