Your question is how do you calculate the potency of a working standard not the formula for assay of a tablet. The answer for the working standard is that you need to have a pure primary reference standard that you use to characterize the working standard. For the assay of a tablet, it is dependent on the sample preparation you chose. The formula you mention is a good start but it misses the weight of the reference standard.

Andrei Blasko Thank you, sir. However, now I am a little confused between the primary reference standard and the working standard

Do you mean the primary reference standard as the internal standard or, the free drug/sample under study?

Because I assumed that the working standard is the free drug/sample under study (HPLC method development and validation).

Your correction on the formula is duly noted sir, but I still don't understand how to calculate the "potency of working standard". Kindly confirm.

The primary reference standard is the one highly purified, including preparative HPLC and available in small quantities. For routine use one can chose a less purified one which is quantitated against the primary reference standard. In this way, the newly qualified reference standard will be available during multiple analysis with its own purity factor. This is not to be confused with the working standard in solution for your analysis prepared from this standard. I hope this helps.