Hi!everybody.
could you please instruct me how to calculate total impurity for drug products with obvious excipients peaks on the chromatography?
Do we need to inject excipients solution before every test and then deduct in calculation?Do anyone have any valued experience in dealing with this issue.

THANK IN ADVANCE

Actually depends on the analyses method. Some methods require injection of placebo solutions, some don't. However if method is validated and if you do know where expient's peaks are, you don't have to inject again. I don't inject plasebo everytime but i do it for mobile phase.

Below there is a formulation 4 single impurity % :


RN CS
—— x ———— x 100 =..Single unknown impurity %
RS CN

RN : Peak area of a single unknown impurity in the chromatogram obtained with sample solution

RS : Peak area of principal in the chromatogram obtained with standard solution

CS : Concentration of standard solution
CN : Concentration of sample solution

and sum of the single unknown impurity is total impurity.

hope helps....

Very thank lime!
But if the offical authority is the analyst,and my impurity method shows big placebo peak on the chromatography. Will the authority inform us and get the excipients to inject placebo solution?