Two suppliers quote 80% silymarin. One is offering a material that will pass your label claim; the other is offering a number produced by a different method. The percentage is the same, the chemistry is not.

What UV-VIS measures

UV-VIS assays measure absorbance at a chosen wavelength and compare it with a reference standard. They are fast, inexpensive, and useful for families of compounds that share a chromophore. Silymarin, total polyphenols, and flavonoid totals are commonly measured this way.

The limitation is specificity. A UV method can count compounds that are not the marker you care about, and it can be influenced by color, turbidity, or the extraction matrix. The result is a legitimate family total, but it is not a single-compound assay.

What HPLC measures

HPLC separates individual compounds before detection, so it can report a specific molecule or a defined set of molecules. Withanolides, ginkgolides, piperine, L-DOPA, and trans-resveratrol are usually measured by HPLC because the individual compounds matter.

HPLC is more expensive and more method-dependent. Two HPLC methods can still produce different results if the column, mobile phase, or reference standard differs, which is why the method should be named on the COA.

Why the numbers differ

A UV silymarin result of 80% and an HPLC silybin result are measuring different things. The UV figure includes several flavonolignans; the HPLC figure isolates one or two. Neither is a lie, but they cannot be compared directly, and a label claim should name the method behind the number.

The same logic applies to ginkgo 24/6, where both marker families are usually measured by HPLC, and to curcuminoids, where the 95% total can hide a wide range of individual curcumin, demethoxycurcumin, and bisdemethoxycurcumin shares.

How to compare quotes fairly

Ask every supplier for the specification, the method, the calculation basis, and a representative COA. Then compare like with like. If one quote is UV and the other is HPLC, the price difference may be a method difference rather than a quality difference.

If your label makes a specific claim, specify the method that supports it. If your label only says "standardized extract", you still need to know which method the certificate uses so your own quality team can release the batch.

  • Specification with marker range and method
  • Calculation basis: as-is or dry
  • Representative COA from the current production lot
  • Chromatogram or spectrum on request
  • Independent verification for a new supplier

What to take away

  • UV measures a family; HPLC separates individual compounds.
  • A percentage without a method is not a comparable specification.
  • Match the method to the label claim, not to the lowest price.
  • Ask for a chromatogram when the marker is the product's main claim.

Cite this note

Rainwood Botanical. "HPLC or UV? Why two suppliers quote different numbers for the same extract." Blog, 2026-10-24. https://ingredients.rainwoodbio.com/blog/hplc-vs-uv-assay-methods/

About this post

Written by the Rainwood Botanical technical team for business-to-business sourcing. It describes analytical and documentary practice, not medical or regulatory advice for a finished product. Market requirements should be confirmed with your regulatory advisor. Read more about our quality and documentation approach and our editorial policy.