accuracy calculations for method development (HPLC)

[mgross]

I am just stumped about accuracy calculation for these samples....

Here's the situation... I am developing a method for sulfadimethoxine oral solution (12.5%). I am developing the assay method according to the USP, so the standard concentration is 0.2 mg/mL - 20mg into 100mL multiplied by the purity factor (simple enough).

Accuracy samples were prepared at 3 levels - 80, 100, 120%.

80% - 1 mL of the 12.5% oral solution (12.5 gm/100 mL) into a 250 mL vol flask. Then 3.2 mL of that solution into a 10 mL vol flask. Conc: 0.16 mg/mL

100% - 1 mL of the 12.5% oral solution (12.5 gm/100 mL) into a 250 mL vol flask. Then 4 mL of that solution into a 10 mL vol flask. Conc: 0.2 mg/mL

125% - 1 mL of the 12.5% oral solution (12.5 gm/100 mL) into a 250 mL vol flask. Then 4.8 mL of that solution into a 10 mL vol flask. Conc: 0.24 mg/mL

My dilemma is how do I calculate the concentration, theoretical concentration, and % recoveries using the area counts from the HPLC.

Thanks!

[Axar]

Easy to done!!!
your 100% concentration is real and theoretical. Then you calculate response factor (area/concentration) for it. With this response factor you calculate theoretical concentrations for 80% and 120%. Then you just compare your real and theoretical concentrations.

[Consumer Products Guy]

Did you spike placebo solution?

[cody84]

I am having the same issue. The product is very viscous. So I adjusted the weights used for sample prep, instead of spiking into matrix, or spiking dilutions. Now the problem is I used the weights to calculate the result and so obviously it was giving the same results for 80, 100 and 120! Haha
Thanks for the response factor info, I can now continue.