# Recovery calculation in related impurities method validation

Hi all,

how to calculate amount added and amount found for a related impurity in the recovery experiment.

can anyone answer to my question.

Thanks
Suri.

You prepare a stock solution of the known impurity with known concentration. Taking 100% as the working concentration for you test method. Then, spiked a quantity of the stock solution in other volumetric flask to get 50, 75, 100, 125, 150% of the known impurities. Add placebo, active or other if required. (please set other more reasonable range for your application)

Prep another 100% working concentration with another stock solution. subject for analysis and use as 100%

Subject for analysis.
the observed signal
recovery = ----------------------------- x 100
the signal obtained (100%)

HI all,

are these formulas mentioned is for a area normalisation method recovery calculations or % W/W method calculations? and what about the response factors affect in the recovery experiment.How can i calculate the recovery with response factors?

Thanks

[quote=bujjikanchi]Eg:

your specification for an impurity A is 0.1%

Preparation of Impurity stock solution:10 mg /100 ml diluent
Standard solution : dilute 1 ml of stock to 100 ml with diluent
Test sample : 10 mg / 10 ml diluent.

Now
Add 0.1 ml of impurity stock to test sample: it gives 50 % spiked
Add 0.2 ml of impurity stock to test sample: It gives 100% spiked
Add 0.3 ml of impurity stock to test sample: It gives 150% spiked

Inject and calculate the % impurity obtained.

% Recovery= (Observed value/ true value) x 100

true value is nothing but theoritical value.[/quote]

Could anybody explain how 50%,100% & 150% spiking calculated, on which basis we have to calculate.(For ex: 0.1ml impurity stock added to test sample gives 50% spike, how it comes, kindly elaborate.

At this point you should not be using area normalization! In fact the curve should be peak response (peak area) versus mass (or concentration).