Validation of Standard Addtion Method for Raw Material Testing

Dear Members,

I am validating a standard addition method of atomic emission spectroscopy for raw/ incoming material testing.

According to ICH guidelines, there are few options to prove the accuracy:
Option 1: be assessed on samples (substance/ product) spiked with known amounts of
Option 2: compare results obtained by an independent procedure. The response factor of the drug substance can be used;
Option 3: comparison of the results of the proposed analytical procedure with those of a second well-characterised procedure, the accuracy of which is stated and/or defined;
Option 4: accuracy may be inferred once precision, linearity and specificity have been

My questions for each option are:

  1. Option 1: Since this method itself is a spiking method, how can I prove the accuracy of this standard addition method?
  2. Option 2: Besides atomic emission/ absorption spectroscopy, is there any other independent methods can be used to prove the accuracy?
  3. Option 3:The method I adopted is a compendial method from USP, no second well-characterised procedure is available.
  4. Option 4: How to prove the accuracy from the precision, linearity and specificity data?

Please kindly advise. Thank you