Polysaccharides by UV, astragaloside by HPLC: reading an astragalus specification
The two numbers we always state separately. In our own quotations we list the polysaccharide assay (UV-VIS) and the astragaloside IV assay (HPLC) on separate lines with their methods named, because a buyer's QA team will ask for both — and because a single blended figure is how misunderstandings start. A typical lot from our standard grade reads 50.4% polysaccharides (UV) and 0.52% astragaloside IV (HPLC).
An astragalus specification is really two specifications stapled together. One describes the polysaccharide fraction, the other a single saponin compound. They are measured by different methods, they respond to different process choices, and quoting them as one number is the most common way an astragalus order goes wrong.
What the UV-VIS figure measures
The polysaccharide assay is a colorimetric method: the carbohydrate fraction is reacted and the resulting colour intensity is read against a standard. It reports the total water-extractable polysaccharide content of the powder. It is a bulk figure, it is inexpensive to run, and it is the figure most suppliers quote first.
Our standard grades run at 20%, 40% and 50% polysaccharides by UV-VIS.
What the HPLC figure measures
Astragaloside IV is one specific triterpene saponin among several in the root. HPLC separates it and quantifies it against a reference standard. The figure is a compound-specific measurement, it costs more per lot to run, and it is the figure that tracks how carefully the extraction was controlled.
Our standard grades run at 0.3% and 0.5% astragaloside IV by HPLC.
Why the two numbers never match
They are not supposed to. A 50% polysaccharide figure and a 0.5% astragaloside figure describe the same powder at the same time — one is measuring sugars by the gram, the other is measuring a single saponin by percentage. Buyers sometimes assume a mismatch means an error. It does not; it means the two assays are doing their jobs.
What the two figures do correlate with is process quality. A lot that holds 50.4% polysaccharides (UV) and 0.52% astragaloside IV (HPLC) together, as our standard production lots do, is a lot where extraction time, temperature and concentration were all controlled.
How to write the specification
| Parameter | How to state it |
|---|---|
| Botanical name / part | Astragalus membranaceus (Fisch.) Bunge, root |
| Extraction solvent | Water, food grade |
| Polysaccharides | ≥ 50% by UV-VIS (state the method, not just the number) |
| Astragaloside IV | ≥ 0.3% by HPLC (or 0.5% for a premium grade) |
| Appearance | Light brown to yellow-brown fine powder |
| Particle size | 80 mesh standard, 100 mesh on request |
| Carrier | None (pure extract) or maltodextrin on request |
The mistake to avoid
Comparing two quotations where one names its methods and the other does not. A supplier who writes "polysaccharides 50%" without the method may be reporting a figure that holds under their method and not under yours. Ask for the method every time — the supplier who answers without hesitation is usually the one who measured.
Frequently asked questions
Why do the UV and HPLC figures never match each other?
They measure different things. UV-VIS reports the total polysaccharide fraction by colorimetric assay, while HPLC quantifies the single saponin astragaloside IV against a reference standard. A typical standard-grade lot reads 50.4% polysaccharides (UV) and 0.52% astragaloside IV (HPLC) at the same time — the mismatch is expected, not an error.
Can you produce to a custom specification?
Yes. Send us the target specification, the methods you want named, and the dosage form, and we will confirm feasibility with the extraction facility before quoting. Alternative assays, mesh sizes and carrier systems are all available.
Which grade should I choose for an immune-support capsule?
Most capsule lines run well on polysaccharides 50% (UV-VIS) with astragaloside IV 0.3% (HPLC). Premium lines and tablet formulations often move up to astragaloside IV 0.5%. If you are unsure, send us your target claim and we will recommend a grade before quoting.
Related: Astragalus Polysaccharides (APS) — full specification, grades and documentation.