Hi Hossein

iF you probably have 3-methyl-2-benothiazolinonehydrazone (MBTH) in the reaction, which react with aldehydes and then result in a blue colored product. the MBTH reacted with aldehydes convert to formazan by reaction with the diazonium salt. this salt produce in the medium by oxidation of excess MBTH and finally forms a blue to blue-green colored product.

Please read more at this article

Colorimetric enzyme-coupled assay for hyaluronic acid determination in complex samples

https://doi.org/10.1016/j.eurpolymj.2017.07.036

I hope it will help

Amin

Read J. Biol. Chem.-1947-Dische-189-98.pdf This is the original method. it still suffers from interference.

This is a better method: Anal Biochem. 1973 Aug;54(2):484-9.

New method for quantitative determination of uronic acids. Blumenkrantz N, Asboe-Hansen G.

Good luck!