Quercetin Adulteration and How Authenticity Is Proven

Why a Purified Active Still Gets Stretched

Adulteration follows economics. Quercetin has a real feedstock cost — Sophora rutin — and a buyer base that mostly checks one number against one specification. Where the number can be made to read high without the material being what the buyer assumed, someone will eventually do it. The four routes below are ranked from most common to most deliberate; only the last is unambiguous fraud, which is precisely what makes the first three so persistent.

Route 1 — Selling Water: the Basis Mismatch

Quercetin dihydrate carries two waters of crystallisation — 10.65% of its weight. Assayed on the anhydrous basis, pure dihydrate reads over 99%; as-is, about 89%. A seller who quotes dihydrate on the anhydrous basis into a buyer who assumes as-is delivers roughly 10% less quercetin per kilogram than the buyer priced — with a CoA that is arithmetically defensible.

This is the single most common quercetin problem, and much of the time it is ambiguity rather than intent: neither party stated the basis, and the cheaper reading won. The commercial effect is identical either way.

What catches it: a specification that names the basis, states the form, and requires water by Karl Fischer — so the as-is content can be reconstructed from the CoA itself. The arithmetic is worked through in our standardisation guide.

Route 2 — Under-Converted Rutin

The hydrolysis from rutin to quercetin costs time, acid or enzyme, and yield. A process stopped early leaves unconverted rutin in the product — cheaper feedstock passed through at finished-product prices. Because rutin is itself a yellow flavonoid of similar solubility behaviour, the blend looks right and passes a UV assay comfortably.

What catches it: HPLC, which resolves rutin as its own peak, and an explicit residual rutin NMT 2% limit on the specification. A supplier who resists a residual-rutin line is telling you something about their process control.

Route 3 — Undeclared Carriers

Maltodextrin, starch and dextrose are legitimate, declared components of formulated grades — a spray-dried dispersible quercetin genuinely needs a carrier. The adulteration is the undeclared version: carrier blended into nominally pure material to make up weight. On a 95% specification the headroom is small, but a diluted lot sold against a lax "complies" assay, or blended to just clear 95% from higher-purity stock, is economically worthwhile at volume.

What catches it: the assay itself if run properly by HPLC; ash and acid-insoluble ash limits for mineral diluents; a bulk-density figure that does not match reference material (carriers are typically denser than fluffy quercetin crystals); and a carrier-declaration clause that converts an omission into document falsification — a materially different decision for a supplier.

Route 4 — UV-Boost Spiking

The deliberate end. If a buyer's assay method is UV spectrophotometry at ~370 nm, the reading can be lifted with anything yellow that absorbs there — cheaper flavonoids such as morin, low-grade flavonoid fractions, or synthetic dyes at the criminal extreme. The material passes the buyer's stated test while containing less real quercetin than declared.

What catches it: HPLC, categorically. A chromatogram shows resolved peaks with retention times; a spiked sample produces peaks that do not match the quercetin reference standard, or an impurity pattern that the Sophora rutin pathway does not produce. This is why the identity requirement should be retention-time correspondence to a reference standard, not "yellow powder, complies" — and why it is worth asking to see an actual chromatogram from a new supplier rather than a typed number.

The Testing Package That Covers All Four

Practical Steps for a Buyer

1. Specify HPLC and the anhydrous basis by name. The two highest-value clauses in a quercetin specification.
2. Require form, water and residual rutin on the CoA. Together they make the drum's real quercetin content computable.
3. Reconcile the arithmetic on every CoA. Anhydrous assay × (100 − water%) / 100 should match any as-is figure quoted. Thirty seconds, and it catches the most common problem in the trade.
4. Ask a new supplier for a chromatogram. A typed "95.2%" is a claim; a chromatogram is evidence.
5. Third-party verify the first batch. Nominate Eurofins, SGS or Intertek for pre-shipment testing on a new relationship, and re-verify periodically thereafter.

SV Botanica confirms quercetin identity by HPLC against a reference standard, assays on the anhydrous basis with form and water stated, and reports residual rutin, ash, bulk density and residual solvent on the Certificate of Analysis. Buyers are welcome to nominate an independent laboratory for pre-shipment verification — see the supplier evaluation guide for how to structure that, or the product specification for the full parameter list.