Discrimination limit for purity test of human insulin by capillary electrophoresis

Because of the inevitable noise in instrumental analysis, a purity test can overlook an illegitimate drug that contains an undesired substance in a higher amount than the prescribed limit. The lowest (average) amount of undesired substance which leads to the right results of the purity test with 95% probability is referred to here as 95% discrimination limit. This paper presents a method for predicting the discrimination limit for the purity test of human insulin in capillary electrophoresis (CE). The theory and experiments show that if the legitimate limit of a degradation product (desamido insulin) is 3.0% of the total amount of the insulin formulation, the 95% discrimination limit in the CE system used in this study is 3.24% desamido insulin. Since the statistical aspects of the purity test are provided by the interpretation of the baseline fluctuation in the instrument, the usual strategy to repeat the instrumental analysis on the same samples is unnecessary in the present study.