Standardisation of Herbal Extracts: Quality Markers and Testing Methods

Marker vs. Active Compounds

Standardisation requires choosing one or more marker compounds — molecules whose concentration is measured and reported on the Certificate of Analysis. In an ideal world the marker is the pharmacologically active compound (curcumin in turmeric, withanolides in ashwagandha, silymarin in milk thistle). In practice, sometimes the active is not analytically tractable, and a stable, easily-measured proxy marker is used instead. Reputable suppliers are explicit about which they have done.

HPLC: The Standard Tool

High-Performance Liquid Chromatography (HPLC) is the workhorse method for marker quantification. A well-validated HPLC method delivers reproducibility under 2% RSD batch-to-batch, with calibration against pharmaceutical-grade reference standards. When evaluating a supplier, ask to see the method validation report — accuracy, precision, linearity range, LOD/LOQ, and specificity. If they cannot share it, the standardisation claim is unverified.

Buyer Checklist

When sourcing standardised extracts, the following items separate a serious supplier from a marketing one:

• Marker compound disclosed by name, not just percentage (e.g., "5% withanolides" should specify total or Withanoside IV).
• Test method disclosed (HPLC, UV-Vis spectrophotometry, gravimetric).
• Reference standard source (USP, EDQM, in-house with characterisation).
• Heavy metals, pesticide residue, and microbial limits tested per pharmacopoeial standards.
• DNA-barcoding or HPTLC fingerprint to confirm botanical identity and rule out adulteration.