Hi All,

I am confused as to what accuracy is required at the LOQ level for impurity methods? I am in-process of a clening mehtod validation. Initially I calculated method's LOQ bsased on the S/N of 10. When I went to perform accuracy at the LOQ level (acceptance criterion of <10% recovery), I found out that S/N of 10 LOQ does not support the accuracy. Since the method will be used for quntitation of the trace amounts in the sample soluiton the accuracy is deemed necessay. In order to get the accuracy needed, not only I had to raise the LOQ to higher S/N which turned out to be S/N of 20 but also use peak height for quantitation. I am not sure, if I am doing the right thing and would like to find out what is everybody's experience regarding LOQ for the impurity methods.

Thanks in advance.

At S/N of 10 and R.S.D. of replicate injections of less than 10%, there is no chromatographic reason not to support recovery between 90% and 110%. If the R.S.D.of replicate responses at this level is more than 20% I would reconsider (troubleshoot) the HPLC method. If not, I would concentrate on the sample preparation.