Calcium sennosides may be estimated by a number of spectrophotometric, spectrofluorimetric and chromatographic (high performance liquid chromatography, HPLC; high performance thin layer chromatography, HPTLC) methods.

Calcium sennosides are extracted into boiling water, which are oxidized with ferric chloride treatment. Subsequent acid hydrolysis releases anthraquinones from glycosides that are extracted into ether. Residue of anthraquinone from evaporated ether solution forms a pink-coloured complex with 1N KOH which is estimated spectrophotometrically.

1. Weigh accurately 10 mg calcium sennosides, transfer into a conical flask, add 25 ml distilled water using a pipette and heat on a boiling water bath for 20 min.
2. Add 2 to 3 drops of water and filter. To 10 ml of the filtrate, add 20 ml 10% aqueous ferric chloride and heat for 15 to 20 min on a water bath.
3. Add 1 ml concentrated HCL and heat till the precipitate dissolves. Cool and extract with ether (4 × 20 ml).
4. Collect the ether layers into a 100 ml standard flask and make up to volume with ether. Mix well and pipette out 10 ml into a clean china dish and evaporate.
5. To the residue add 10 ml 1N KOH, mix uniformly and determine the absorbance at 500 nm using 1M KOH as blank.

Calculate the percentage sennoside content based on the extinction value of sennosides in terms of free anthraquinoines which is 200 at 500 nm.