Question

Determination of anthocyanins from blueberries:

(Crush 3.0 g immediately before use. To 2.5 g of the crushed, accurately weighed drug,
add 47.5 ml of methanol R. Stir mechanically for 30 min. Filter into a 50.0 ml volumetric
flask. Rinse the filter and dilute to 50.0 ml with methanol R. Prepare a 50 fold dilution of
this solution in a 0.1 per cent V / V solution of hydrochloric acid R in methanol R.
Measure the absorbance of the solution at 528 nm using a 0.1 per cent V / V solution of
hydrochloric acid R in methanol R as compensation liquid.)

Calculate the percentage content of anthocyanins expressed as cyanidin 3-O-glucoside
chloride, using the following expression:

A * 5000 / 718 * m

(718 = specific absorbance of cyanidin 3-O-glucoside chloride at 528 nm
A = absorbance at 528 nm
m = mass of substance to be examined in grams)

QUESTION: Why is the absorbance measured at 528 nm?

Answer 1

From the reported papers it is mentioned that by performing the different experiments and also by changing the concentration of anthocyanins according to beer Lambert's law A=ecl. It is observed that by repeating change in wavelengths at a wavelength at 528nm anthocyanins are showing maximum intensity at the visible region so it is needed to measure absorbance at 528nm.