Senna is sold on a sennoside percentage — but that number depends entirely on how it was measured. A UV assay and an HPLC assay on the same batch will not read the same, and comparing across them is how buyers over- or under-pay.
Senna extract is sold on a sennoside percentage — 20%, 40%, 60%. But that single number depends entirely on how it was measured. A UV-spectrophotometric assay and an HPLC assay applied to the same batch of senna will not return the same figure, and comparing grades across the two methods without accounting for this is one of the most common ways buyers over- or under-pay.
What the Sennosides Actually Are
The laxative activity of senna comes from dianthrone glycosides — principally sennosides A and B, with sennosides C and D also present. These are the compounds a standardisation assay is trying to quantify. Because sennoside B is the common reference, UV results are frequently reported “calculated as sennoside B”.
The UV Method: Total Sennosides as Sennoside B
The classic pharmacopoeial approach for senna is a UV-spectrophotometric assay. In simplified terms, the sennosides are converted and their colour/absorbance measured, and the total is calculated as sennoside B against a reference. UV is robust, inexpensive and well suited to routine standardisation to a target percentage. Its limitation is that it reports a total figure rather than resolving individual sennosides, and the result is method-dependent.
The HPLC Method: Resolving Sennosides A and B
High-performance liquid chromatography separates the individual dianthrone glycosides, so a result can be reported as sennosides A and B specifically. This gives a more selective, composition-aware number and is valuable where a tight or pharmacopoeial specification calls for defined A&B content, or where identity needs to be confirmed alongside potency.
| UV (as sennoside B) | HPLC (sennosides A&B) | |
|---|---|---|
| Reports | Total sennosides | Individual A & B |
| Typical use | Routine grade standardisation | Tight / pharmacopoeial spec, identity |
| Selectivity | Lower — total fraction | Higher — resolves components |
| Cost / speed | Lower cost, fast | Higher cost, more information |
| Comparability | Compare only vs other UV figures | Compare only vs other HPLC figures |
The buyer's rule: never compare a UV percentage against an HPLC percentage as if they were the same scale. A “20% by UV as sennoside B” and a “sennosides A&B by HPLC” describe the material differently — require the method next to every number.
What to Put on the Specification
For senna, a complete potency line states three things: the percentage, the method (UV or HPLC), and the reference basis (calculated as sennoside B, or sennosides A&B). If any of those is missing from a quote or CoA, the number cannot be reliably compared or verified. This is also a first line of defence against adulteration, since a method-backed assay is harder to fake than a bare percentage.
To place this in a full purchasing decision, see the senna buyer's guide; or view the Senna Extract with its grade options.
Specify Sennosides the Right Way
Percentage · method (UV or HPLC) · reference basis (sennoside B or A&B) · batch CoA