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We are dealing with a very low level analyte in a complex powder blend - 0.0006% w/w
Recognizing that larger sample sizes improves consistency we have gone from 1 gram, to 2 gram, to 5 gram sample prep procedures which involves extraction with a solvent, evaporation, reconstitution in water for injection.
RSD on all of these were not good. We were going to move up to 10 gram sampling when it hit me that I might just be dealing with such a low level of dilution in a powder blend (batches are in hundreds of kilograms) for this particular analyte that in order to achieve appropriate precision levels I will need to sample sizes in the thousands of grams before consistency and a proper RSD can be achieved.
I scanned the literature for typical drug concentrations in tablets and found dosages at the mg level for typical tablet sizes. My 10 gram sample will have an estimated analyte amount of 6 ug.
This question is not about sensitivity of the instrumentation or of the ability to extract out the analyte itself from the other materials in the blend - that is not the problem. The problem is that I think it could be possible that the analyte is so dilute in this powder blend that sample sizes of under 100 grams would not "cast a wide enough web" so to speak to generate consistency between samples and a proper RSD when validating for precision. Am I right? Am I wrong? Am I down some rabbit hole in my thinking that is nonsensical?