Two ashwagandha CoAs can both say "5% withanolides" and describe genuinely different materials — because the number depends entirely on how it was measured. Gravimetric and HPLC assays answer different questions, and confusing them is the most common way buyers overpay or under-spec. Here is what each method measures, why the numbers diverge, and which one to put on your purchase order.
Two Methods, Two Questions
The withanolide figure on an ashwagandha CoA can come from two very different analytical approaches:
- Gravimetric assay answers "how much of the withanolide-rich fraction is in this powder, by weight?" It captures a broad band of withanolide-type material and is the common trade method for full-spectrum root grades. It tends to read higher.
- HPLC assay answers "how much of these specific, named withanolides is present?" It separates and quantifies individual compounds against reference standards. It is compound-specific and tends to read lower for the same material.
SV Botanica's stock 5% grade is assayed gravimetrically (5.35% w/w on the reference batch), and an HPLC withanolide test report is available per batch to confirm the compound-specific profile against named markers. Buyers who need a defined HPLC profile on their incoming-goods spec can request it on the same root material — one extract, reported by both methods — so the gravimetric figure is never the only data point you have to rely on.
Why the Numbers Diverge
| Aspect | Gravimetric | HPLC |
|---|---|---|
| What it measures | Total withanolide-rich fraction by weight | Specific named withanolides |
| Typical reading | Higher, broader | Lower, specific |
| Specificity | Group-level | Compound-level |
| Best for | Full-spectrum root grades, trade | Defined-profile labels, monographs |
| Withaferin A visibility | Not resolved individually | Can be quantified separately |
The key point: a higher gravimetric number is not automatically a stronger extract than a lower HPLC number. They are measuring different things. Comparing a gravimetric % from one supplier against an HPLC % from another is an apples-to-oranges mistake.
How to Read an Ashwagandha CoA
- Find the method next to the number. "Withanolides 5.0% by gravimetric" and "withanolides 2.5% by HPLC" can describe comparable material.
- Check the plant part. A high number from leaf or whole-plant material is not the same product as a root grade — see root vs leaf.
- Ask whether withaferin A is reported. HPLC can resolve it; gravimetric cannot. For a root grade, a low withaferin A is reassuring.
- Confirm identity. TLC or HPLC identification should accompany the assay.
Which Should You Specify?
Rule of thumb: if your label simply states "ashwagandha root extract, standardised to X% withanolides" for general wellness, a gravimetric grade is usually appropriate and cost-effective. If your label, a pharmacopoeial monograph or a customer specification names defined withanolides or a withaferin A limit, specify HPLC. State the method explicitly on the purchase order so quotes are comparable.
For how this fits the wider purchasing decision, return to the ashwagandha extract buyer's guide; for contaminant and labelling rules, see regulatory & compliance.
Need a Defined Withanolide Assay?
Gravimetric 5% in stock · HPLC withanolide test report per batch · withaferin A on request · CoA per batch