Rutin can be estimated colorimetrically by detection of the red colour it forms upon reduction with magnesium amalgam and hydrochloric acid. This is a useful method for the estimation of rutin content in both plant extracts and in pharmaceutical dosage forms.

It may be more simply assayed spectrophotometrically by measuring its absorption in ethanol at 259 nm and 363 nm. The percentage rutin content may be estimated from an absorption curve of a standard rutin solution.

1. Sample preparation: Dissolve 0.5 g of the sample in 50 ml HPLC 80% methanol and filter. Take 2 ml of the filtrate in a 50 ml standard flask. Add 2 ml double-distilled (dd) water and 5 ml ammonium molybdate and dilute the mixture to 50 ml with dd water.
2. Standard solution: Dissolve 0.02 g of rutin in 50 ml HPLC 80% methanol. Take 1 ml of this solution in a 50 ml standard flask and add 2 ml dd water, 5 ml ammonium molybdate and make up to required volume with dd water.

Measure the absorption of the sample against dd water as blank at 360 nm. Percentage of rutin content in the sample is calculated by

where A_sample is the absorbance of the sample at 360 nm, A_standard absorbance of the standard solution at 360 nm, C concentration of the standard solution of rutin, g/ml, W the weight of the sample in g, 2 volume of the sample.