standard for HPLC assay.

[kamel]

Hello all,
I would like to weight 100mg Atorvastatin from Atorvastatine calcium,
Potency as Atorvastatin is 91.5%,
Potency as Atorvastatin calcium is 94.8%,
How can I proceed? Weight (100/94.8%) to have 105.485mg and use 91.5% for calculation, or weight directly 100/91.5%=109.289mg and use the same potency (91.5%).
I would like to know more about this parameter (potency)
Thank you for your answer.

[tom jupille]

Potency in this context means the percentage of the species of interest in the material. In other words, 91.5% of the mass is atorvastatin, and 94.8% is atorvastatin + calcium. If you want 100 mg of atorvastatin (without the calcium), 109 mg is the correct amount to use.

[kamel]

dear tom jupille,
Thank you very much for your reply, I asked somme chemists and they gaves me the same responce..
I used to use 105mg, but fortunatly, from the SOP, I can weight ±10% of the requeste weight..

thank you very mach..you'r helpfull.
good continuity.

[MaryCarson]

I would recheck your SOP. It may allow 10% difference in weight taken, but my guess is you still have to do the calculation exactly right with the weight used. Otherwise, you have introduced a 4% error in all your results by using 105 mg instead of 109 mg.