Hi guys, I am new in validation field. it is the method for impurities. I am working on Accuracy with duplicate samples prep at conc. 0.1,0.5,1.0,1.5,2.0% of the working conc of 100 micro gram/ ml. How would you prepare the samples? I am thinking of preparing the 100% solution as the stock sample and diluting the stock sample to get the desired conc. Each spl will be prepared from stock spl by volumetric dilution. Exactly the same way as we work on linearity. Is it the correct way of sampl prep? Please input your thoughts. Help will be appreciated.

Accuracy generally determined from recovery test,so you can prepare analyte conc. as you described above,but at the same time you also should consider the conc. of matrix at different recovery level.
For impurity accuracy test of drug substance or product,you should keep drug active at the same conc. level.

Hope helpful!

Anonymous 2 . Your suggestion is helpful. I will be running this method for the first time. Somebody else developed the method. Test protocol says to prepare the solutions at above concentration with the active and 1/100 of the placebo tablet. The working standard conc. in the impurities method is 100 microgram/ml. I was told by another chemist to weigh the active and equivalent placebo everytime to prepare the sample solutions instead of preapring the stock sample and diluting it to desired concentrations. Please suggest if the stock solution prep and further dilutions is the correct way or weighing the active and placebo evertime to prepare the spl solutions at different conc. levels?

thank You!

One thing more to add to the above question. impurities are not available so we will be preparing solutions with placebo powder(by grinding 10 tabs) and active only. it is written in the protocol that linearity will be done with active at the same concentrations as in accuracy. Is everything right with protocol? I donot have experience in impurities validations. Please shed some thoughts and experience.

For an accuracy experiment, you should definately not be diluting the placebo. It should be present at the same amount (nominal sample weight)in each solution. In general, you can either weigh in the active at the different levels or use a stock solution of the active and spike volumetrically, whichever you prefer. You can use either method because you are not trying to show that you are fully extracting the active fron the matrix, that is the purpose of an extractability study. All you are showing is that you can accurately quantify the active across the range of the method in the presence of the nominal amount of matrix, and that the matrix is not causing a significant bias in the result.

Also, for method validation in general, consult ICH Q2A and Q2B. They can be found at www.ich.org

Thank You so much for your response. all my doubts are clear now. I was doing it for the first time. Thank you for adivising me.