Quercetin looks like the easiest botanical purchase on the market: a single defined molecule, a purity number, and dozens of sellers quoting it. That apparent simplicity hides the industry's neatest specification trap — two quotations that both say "95%" can describe materials several percentage points apart in real quercetin content, and both suppliers can defend their number. This guide covers the grade families, the assay-basis arithmetic, and what a genuine Certificate of Analysis must show.
What Is Quercetin Extract?
Quercetin is a flavonol — 3,3′,4′,5,7-pentahydroxyflavone — and the most abundant flavonoid in the human diet, present in onions, apples, capers and tea. Commercial quercetin, however, is not concentrated from any food crop. It is produced from the flower buds of Sophora japonica L., which accumulate the glycoside rutin at 15–20% or more — a level no other practical raw material approaches. Hydrolysis cleaves rutin's sugar and the liberated quercetin is crystallised and purified.
The consequence for a buyer: this is a purified botanical active, not a crude extract. There is no 4:1 or 10:1 ratio to argue about, no marker-versus-matrix debate. The material is specified like a phytochemical — a purity percentage, an impurity profile and a crystalline form — and the buying skill lies in reading those three correctly.
The Four Commercial Grades
- Quercetin 95% — the mainstream supplement grade, assayed by HPLC on the anhydrous basis. The default choice for capsules and tablets.
- Quercetin 98% — a high-purity grade for premium and low-excipient formats, where the tighter impurity profile justifies its premium.
- Quercetin dihydrate — the same molecule carrying two waters of crystallisation. A legitimate, widely used form — provided it is declared and assayed on a stated basis.
- Enhanced-bioavailability formats — glycosylated quercetin and lecithin co-processed (phytosome-style) grades developed around the aglycone's poor water solubility, with quercetin content declared per grade.
These are different materials at different prices. A quotation for "quercetin, $X/kg" that does not name the form and the basis is not yet a quotation.
The Assay-Basis Trap
Here is the arithmetic every quercetin buyer must be able to do. The dihydrate's two water molecules make up roughly 10.7% of its weight. A perfectly pure quercetin dihydrate therefore assays at about 89% as-is — and over 99% on the anhydrous basis. Same powder, same purity, two honest numbers.
The trap in practice: a supplier quotes "quercetin 95%" for dihydrate material assayed on the anhydrous basis, while your specification silently assumes 95% as-is. You receive a compliant CoA and roughly 85% actual quercetin per kilogram of powder — about 10% less active than you budgeted, at a price that looked competitive precisely because of it. The fix costs one sentence: "Quercetin NLT 95.0% w/w by HPLC, calculated on the anhydrous basis; form and water content by Karl Fischer to be stated on the CoA." The full arithmetic is worked through in our guide to HPLC purity and standardisation.
What a Genuine Quercetin CoA Must Show
These are the specification limits SV Botanica supplies high-purity quercetin against. A complete, trustworthy CoA should carry every line below.
| Parameter | Specification / Limit | Method |
|---|---|---|
| Identification | Retention time corresponds to quercetin reference standard | By HPLC / UV |
| Quercetin (declared basis) | NLT 95.0% w/w, anhydrous basis | By HPLC |
| Form | Anhydrous or dihydrate — stated | Declaration |
| Water (dihydrate) / LOD (anhydrous) | 8–12% KF / NMT 5.0% | Karl Fischer / IP-2014 |
| Residual rutin | NMT 2.0% | By HPLC |
| Total ash / acid-insoluble ash | NMT 1.0% / NMT 0.5% | IP-2014 |
| Bulk density | 0.15–0.40 g/ml, reported | IP-2014 |
| Residual solvent (ethanol) | NMT 5,000 ppm | By GC |
| Lead / Arsenic / Cadmium / Mercury | NMT 1.0 / 1.0 / 0.3 / 0.1 ppm | ICP-MS |
| Pesticide residues | Complies (EU MRL, on request) | GC-MS / LC-MS/MS |
| Ethylene oxide | Not treated — declaration provided | LC-MS/MS (on request) |
| Microbiology (TPC / Y&M / pathogens) | NMT 1,000 / NMT 100 / negative | USP <2021>/<2022> |
| Shelf life | 36 months from manufacture | — |
Two lines deserve particular attention. Residual rutin is a direct readout of how completely the hydrolysis ran — under-converted material carries excess glycoside that inflates powder weight without contributing free quercetin. And the water/LOD line paired with the stated form is what makes the assay basis verifiable rather than a matter of trust.
The Formulation Questions to Settle Before You Order
Quercetin's purity makes the chemistry simple; its physics is where orders go wrong. The powder is light — bulk density can run as low as 0.15 g/ml — dusty, electrostatic and poorly wettable. Ask three questions before committing:
- What is the batch bulk density? A capsule line validated at 0.35 g/ml will underfill at 0.18. Have it reported per batch, and specify a range if your equipment needs one.
- What mesh cut? 40–80 mesh is standard; tighter cuts and granulated material are available for flow-critical processes.
- Is the format water-based? If yes, the standard aglycone is the wrong grade — see the applications guide for the enhanced-format options.
Sourcing and What to Ask Your Supplier
India offers mature purification and standardisation capability with NABL-accredited analytics, competitive pricing and documentation practices built for regulated markets — CoA, MSDS and declarations covering ETO, irradiation and GMO status issued per batch. When evaluating quercetin suppliers, request as a minimum:
- Batch-specific CoA stating purity, form and assay basis, with methods named
- Water by Karl Fischer (dihydrate) or loss on drying (anhydrous)
- Residual rutin figure by HPLC
- HPLC identity against a reference standard, with the chromatogram available
- Heavy-metal report by ICP-MS with numeric limits for Pb, As, Cd, Hg
- Bulk density reported, mesh stated, carriers declared by name if any
- Pesticide residue report against EU MRL, and a non-ETO declaration
- Declarations: non-irradiated, GMO-free, allergen status
Our companion quercetin supplier evaluation guide turns this into a scored checklist. SV Botanica supplies 95%, 98%, dihydrate and enhanced-bioavailability quercetin from certified facilities in India, with full documentation available before any bulk commitment and samples for qualified buyers.
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