# The limit for weighing sample

Dear Sirs,

My manager asked me about the limit for weighing sample. For example, I am perform assay Danazol in capsule as USP: “Accurately weigh the contents of not less than 20 Capsules. Mix the contents, and transfer an accurately weighed portion of the powder, equivalent to about 100 mg of danazol”.

The theoretical weight of each danazol capsule is 320.5mg and the labeled amount of danazol in each capsule is 200 mg

As USP method, I must weigh the sample equivalent to 100 mg = 320.5/2 mg (160.25mg) of content powder. My manager told me that we can weigh ± 10% the normal weigh. It means I only can weigh the content powder from 144.225 mg to 176.275 mg. If the weight of sample is out of this range, the assay result is not acceptable.

But I can not find in the USP for this requirement.

Thank you very much!

Under USP terms and definitions, about meaning within 10%. Your manager is right. But if you have a requirement to deviate from this, I cannot see why you couldn’t with proper justification and validation. In general I would keep the range narrower so that your sample will be closer to standard.

Question: why does USP have the analyst weigh the content of the 20 capsules? Love that USP !!! I can understand the USP desire to obtain a representative sampling.

You most likely have your own company SOP or test procedure for this assay (OK, it might simply state to use the current USP assay). So weigh within the 144.225 mg to 176.275 mg range and discard that weighing if not within the range. If you are out of weighing range for a sample, you simply have no cGMP data data, shouldn’t even assay. Your result is not just “unacceptable”, you have no result, as the procedure wasn’t followed correctly.

That’s the way I understand these things. I used to be smart.

Its not Love or Hate towards USP

Its worst case study. checking assay by crusing one or two tablets may give some times 100% or sometimes 96%,

worst case study : crushing more tablets and mix together and anlayse gives average assay of your batch size, probably the number can be 20 tablets.

weighing 10% deviation is clearly addressed in GENERAL NOTICES of USP Books.
General notices are published in each volume of USP.
The index of statement is About

about : 10% consideration of deviation .

Best Regards,
Bujji Reddy Kanchi.
+91-9676749937