Qualifying a supplier for a purified active looks easier than for a crude botanical — one molecule, one number. In practice the qualification hinges on discipline around exactly that number: which basis it is calculated on, what sits in the other five percent, and whether the supplier's documents let you reconstruct both. This is a weighted framework for scoring quercetin suppliers on what predicts a repeatable material — and the red flags that should end a conversation before scoring begins.
Before You Score Anyone: Three Disqualifying Red Flags
These are not point deductions. They are reasons to stop.
- A quotation or CoA that states a percentage without a basis. "Quercetin: 95%" with no anhydrous/as-is clause and no water figure is not a specification — it is a number chosen to be read favourably. On this material specifically, basis silence is the oldest trick in the book.
- Assay by UV spectrophotometry. Quercetin's main economic adulterants — rutin, cheaper yellow flavonoids — absorb at the same wavelength. A UV assay on quercetin verifies almost nothing, and a supplier running one as their release method has chosen not to see.
- Refusal to allow third-party pre-shipment testing. There is no legitimate commercial reason to refuse. A supplier confident in their material treats independent verification as a sales tool.
On price comparison: quercetin quotations cannot be compared until they are normalised to the same basis. Convert every quote to price per kilogram of anhydrous quercetin delivered — as-is content ≈ anhydrous assay × (100 − water%) / 100 — before ranking. A "cheap" dihydrate quoted on the anhydrous basis routinely comes out more expensive per delivered kilogram than a dearer anhydrous offer. Collect five quotes, normalise, discard the outliers, and treat the middle as the market.
The Scoring Framework
Weighted to 100 points across five dimensions. Score each supplier independently, ideally before you see their price, so commercial pressure does not colour the technical assessment.
1. Assay Discipline and Documentation — 30 points
| Criterion | Points |
|---|---|
| Batch-specific CoA (not a generic specification sheet) with methods named per parameter | 7 |
| Assay by HPLC against a reference standard, basis explicitly stated | 7 |
| Form declared; water by Karl Fischer (dihydrate) or LOD (anhydrous) present | 6 |
| Residual rutin reported with a numeric limit | 5 |
| Chromatogram available on request | 3 |
| Carriers and excipients declared by name and percentage | 2 |
2. Testing and Compliance Readiness — 25 points
| Criterion | Points |
|---|---|
| Heavy metals by ICP-MS with numeric per-element limits (not "complies") | 6 |
| Full USP microbiological panel including pathogens | 5 |
| EU pesticide MRL screening available with a real report | 5 |
| Non-ETO declaration, with LC-MS/MS testing available | 4 |
| Testing at a NABL-accredited (or ISO 17025 equivalent) laboratory | 5 |
Pesticide and ETO lines matter less for a recrystallised purified compound than for a dried herb — purification strips most field residues — but EU-bound consignments still get asked, and a supplier who can produce the reports has shipped seriously into regulated markets. That is what the points are really scoring.
3. Traceability and Sourcing — 15 points
| Criterion | Points |
|---|---|
| Source route declared: Sophora japonica flower bud via rutin conversion | 5 |
| Batch traceable to raw-material (rutin) lot | 4 |
| Country of origin and processing site stated | 4 |
| Certification chain intact where organic or kosher/halal is claimed | 2 |
4. Consistency and Capability — 15 points
| Criterion | Points |
|---|---|
| Three consecutive batch CoAs provided showing assay and water consistency | 6 |
| Multiple grades available (95%, 98%, dihydrate, enhanced formats) | 4 |
| Bulk density reported per batch; granulated/mesh options confirmed in writing | 3 |
| Retention samples held and available | 2 |
The three-consecutive-batch request is the most underused tool in procurement. One CoA shows a supplier's best day; three consecutive ones show what the process holds. On quercetin, watch the water figures across batches as closely as the assay — drifting water on a nominally anhydrous grade means inconsistent drying, and your fill weights will inherit it.
5. Commercial Terms and Responsiveness — 15 points
| Criterion | Points |
|---|---|
| Incoterms quoted properly (EXW/FOB/CIF/CIP) to your named destination | 4 |
| Written payment terms on a proforma invoice, not verbal | 3 |
| Realistic stated lead times, including documentation | 3 |
| Samples supplied with the same CoA standard as bulk | 3 |
| Technical questions answered by someone who understands the chemistry | 2 |
A one-question test for that last line: ask what their dihydrate assays as-is. A commercial contact who answers "about 89% for pure material — here is the arithmetic" has real technical depth behind the desk. One who answers "95%" has just failed the most important question in the category.
Interpreting the Score
| Score | Reading |
|---|---|
| 85–100 | Qualified for bulk supply. Proceed to sample and pre-shipment verification. |
| 70–84 | Workable with conditions. Identify the gaps and require them closed in writing before first bulk order. |
| 55–69 | Suitable for trial quantities only, with independent testing on every lot. |
| Below 55 | Not a supplier for a regulated market. The documentation burden will fall on you. |
The Sample Stage Is Part of the Assessment
- Does the sample CoA state the basis and water content? If the sample document is basis-silent, the bulk documents will be too.
- Does the physical sample match the density claim? Weigh a known volume. Quercetin at 0.35 g/ml when the reference material runs 0.2 invites the carrier question.
- How long did it take? Seven to fourteen business days including documentation is normal for India-origin material.
- Did they ask you anything? A supplier who does not ask about your format, dose per serving or whether the application is water-based will not catch a grade mismatch before it becomes your problem.
First-Order Protocol
- Nominate an independent laboratory — Eurofins, SGS or Intertek — for pre-shipment sampling and testing, at your cost. Have them test assay and water, on your stated basis.
- Reconcile the independent report against the supplier CoA line by line. Small variances are normal; a directional pattern is not.
- Retain your own sealed, dated sample of the shipped lot for the shelf life of the material.
- Re-verify independently at batch three and then annually, or on any change of processing site.
SV Botanica supplies bulk quercetin from certified facilities in India with batch-specific CoAs from NABL-accredited laboratories — basis stated, water and residual rutin reported — and welcomes buyer-nominated third-party pre-shipment testing. The full parameter list is on the quercetin product page; the specification logic behind it is in the buyer's guide, and the failure modes it defends against are in adulteration and authenticity.
Source High-Purity Quercetin from India
Quercetin NLT 95% by HPLC on a declared basis · 98%, dihydrate & enhanced-bioavailability grades · CoA-backed · samples for qualified buyers