Digoxin content in plant extracts, formulations, body fluids etc. may be determined by innumerable methods of assay based on colorimetry, fluorimetry, gas liquid chromatography, HPLC and radioimmunoassay to name a few.

A. Method I (IP Method)

1. Weigh accurately 40 mg and dissolve it in sufficient 95% ethanol to produce 50 ml.
2. Transfer 5 ml of this solution into a 100-ml standard flask and make up the volume with the same solvent.
3. To 5 ml of this solution, add 3 ml of alkaline picric acid solution (see tests for andrographolides) and set aside in the dark for 30 mins. This is the test. Repeat steps 1 to 3 on a standard sample of digoxin to make the standard solution.
4. Measure the absorbances of both the test and standard solutions at the maximum at about 495 nm against a blank made up of 5 ml 95% ethanol and 3 ml alkaline picric acid solution.
5. Calculate the content of digoxin from the absorbance of the standard of the known quantity taken for the assay.