Is there any specific trend or graph at which assay of API decrease with moisture content?
Assay of API is inverse proportional to the moisture content.
i.e; weight of the sample varies due to the presence of M.C in API.
Ex: 1) If API having M.C about 3.0%, then the obtained assay result is considered as is basis.
2) In assay calculation formula, if we subtract the M.C then the obtained result is considered as anhydrous basis…
From the above two cases, you can get different assay result for the same API.
Simple as if you are weigh 100 mg api having 2℅ moisture than its actual purity is 98℅ instead of 100. Same way moisture increased and purity decreased