3.2.1. Specificity
RA, A1 and IS chromatograms obtained from processed blank plasma samples were examined to determine the degree of interference by endogenous plasma components. Fig. 4(a)–(c) shows typical chromatograms of blank plasma, plasma spiked with IS and plasma samples with A1 and RA. The retention times of PPD (IS), RA, and A1 were 1.15, 1.38, and 1.53 minutes, respectively, with no endogenous interference or matrix effects.