Milk thistle extract is usually sold as 80% silymarin. That figure is commonly a UV family total. Silybin is one compound inside the family, and an HPLC silybin result will be a different number. Both can be legitimate; they cannot be used interchangeably.

1. What 80% silymarin actually measures

Silymarin is a mixture of flavonolignans, including silybin A and B, silychristin, silydianin, and others. A UV method measures absorbance from the mixture against a reference standard and reports a family total. It is fast, widely used, and accepted in many commercial specifications.

The number is method-dependent. A different reference standard, wavelength, or sample preparation can shift the result. That does not make the method invalid, but it means the certificate must state the method and the basis, and two suppliers' UV figures should be compared with care.

2. What silybin by HPLC adds

HPLC separates the individual flavonolignans before detection, so it can report silybin A and B or a total silybin figure. This is more specific than a UV family total, and it is the right number when the label, a study, or a customer specifically names silybin.

An HPLC silybin result is usually lower than a UV silymarin result for the same material because it counts a subset of the family. Seeing '80%' on one certificate and '30% silybin' on another does not necessarily mean the second material is weaker; it means the two documents are measuring different things.

3. Where labels go wrong

The common error is a label that says 'milk thistle extract 80% silymarin' while the supporting COA reports only silybin by HPLC. Another is a marketing claim built on a silybin figure while the specification is a UV family total. Both create a gap between the claim and the document that a retailer or a competent authority can find.

Decide which number the label will use, then write the specification around that number. If the label names both, the COA should report both, with methods.

4. How to compare two quotes

Ask both suppliers for the specification, the method, the calculation basis, and a representative COA. If one quote is UV silymarin and the other is HPLC silybin, normalize before comparing price. Ask each supplier to quote the same marker and method so the commercial comparison is meaningful.

If the supplier cannot explain why the numbers differ, that is a signal about the depth of their technical support, not only about the material.

  • Same marker definition: silymarin family or silybin
  • Same method: UV or HPLC
  • Same basis: as-is or dry
  • Same plant part and extract ratio
  • Same carrier and particle size

What to take away

  • 80% silymarin by UV and 80% silybin by HPLC are different measurements.
  • Match the specification to the number your label actually uses.
  • Normalize marker, method, and basis before comparing prices.
  • Ask for both values when the brand story names both.

References and further reading

Cite this note

Rainwood Botanical. "Silymarin 80% by UV is not silybin 80% by HPLC." Blog, 2026-10-24. https://ingredients.rainwoodbio.com/blog/silymarin-uv-vs-silybin-hplc/

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.