Experimental Considerations.Typically, known amounts of related substances

and the drug substance in placebo are spiked to prepare an accuracy sample of

known concentration of related substance. According to the ICH, accuracy should

be determined using a minimum of nine determinations over a minimum of three

concentration levels covering the range specified. Similar to the experiments used

in linearity (see Section 3.3.3) the related substances and the drug substance can

be weighed directly into the placebo or serial dilution from a stock solution can be

used. When no authentic sample is available for preparing the spiked solutions,

one may determine method accuracy by comparing the results of the original

method with that of the orthogonal method (e.g., capillary electrophoresis, thin-

layer chromatography, normal-phase HPLC).