A percentage needs a denominator
Before ranking two reported percentages, ask what mass each percentage refers to: the material as received, a defined dry basis, or the genuine extract before excipients. EMA distinguishes genuine extract and added excipients in its medicinal-product declaration framework.[1] For a commercial comparison, preserve both the supplier’s original wording and the laboratory’s calculation basis. Do not silently rewrite “dry basis” as “carrier free.”
Ask what was removed from the denominator
Request the exact correction formula and the measurement used in it. If the laboratory uses loss on drying, ask what procedure generated that value and whether it was measured on a representative sample from the same lot. If a water-specific result is used instead, record that distinction. These are different reporting choices; this guide does not supply a universal correction factor or prescribe a moisture method for every extract.
Keep the arithmetic auditable
A useful comparison worksheet records the original assay, original reporting basis, correction measurement, units and resulting comparison basis in separate fields. Ask the laboratory to confirm the calculation instead of reverse-engineering an unexplained COA percentage. Never use a correction to conceal an out-of-specification original result or to select whichever basis looks more favorable. The agreed purchase specification remains the decision reference.
A conversion does not validate the assay
ICH Q2 discusses accuracy under regular test conditions, including the matrix and sample preparation.[2] Changing a denominator is not evidence that an analytical method measures the intended constituent correctly in a carrier-containing powder. Keep method suitability and reporting arithmetic as separate review items. If either is unresolved, do not turn the converted number into an equivalence claim between two suppliers.
Supplier checklist for a comparable quotation
Ask for the supplied composition, whether carriers are included in the assay sample, result units, original and corrected basis, method revision and underlying correction result. Confirm the lot and sample handling history. Request a written explanation if a technical sheet uses dry basis while the batch report omits the basis. Do not assume sales copy and the laboratory report use the same denominator merely because their percentages resemble one another.
Use the result within its boundary
A reconciled reporting basis can improve a purchasing comparison, but it does not establish botanical identity, complete chemical equivalence or application stability. Retain the unconverted result and explanation with the decision record. No worked example here is a real COA, and no numerical assay, carrier percentage or acceptance limit for a ZL product is asserted. Seek a product-specific specification before making a supply decision.