USP Benzocaine Assay Result Help

[DagOnChrom]

I'm trying to calculate the assay results for a Benzocaine raw material I ran. The results need to be 98.0%-102.0% Benzocaine.

The only formula on the USP method, is to calculate the quantity, in mg, of Benzocaine.

1000C(rU/rS)

Where C is the concentraion, in mg per ml, and rU and rS are the peak responses obtained from the Assay preparation and Standard preparation. 1000 is the dilution factor.

My calculation.
1000(0.0245mg/ml)(34822.20/35285.529)=24.18

My mass of the sample I weighed out was 23.9 mg.

So is my assay precentage found by (Sample Mass/Calculated Quantity)*100=(23.9/24.18)100=98.8%

Is it found by (Calculated Quantity/ Sample Mass)*100=(24.18/23.9)100=101.2%

Or is it some other formula I can't think of.

Thanks!

[tom jupille]

Assay percentage would be (what you got)/(what you should have gotten). In this case, 24.2/23.9

[Consumer Products Guy]

Love that USP!!!

[DagOnChrom]

Thanks for the help.