Use of the total error approach to evaluate the performance of a semi-quantitative immunological method (BIACORE method) for detecting sulfamethazine in bovine milk

A semi-quantitative immunological method (BIACORE method) for detecting sulfamethazine in bovine milk was developed and validated using the total error approach. The acceptance limits were set at ±40% and the risk of procedure of (1−β) proportion measurements falling outside the acceptance limits was chosen at 5%. Different response functions were tested on the basis of the accuracy index (IA). The best model was a weighted (1/X2) quadratic regression and the simplest one was an unweighted quadratic regression. This approach identified the weak point of the method, which was precision. Finally this BIACORE method was able to detect positive samples containing sulfamethazine in the dosing range between 50 and 150 ng/ml.