Chromatography Forum

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.

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.

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.

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.