The increasing use of chitosan encourages the search for fast and sensitive methods to quantify its concentrations in water solutions. Recent colorimetric studies have suggested quantification by binding chitosan to Cibacron Brilliant Red 3B-A (BR) dye and measuring the absorbance at 575 nm related to the complex that is formed. This study presents an improved colorimetric technique based on the complexation reaction between BR and chitosan. However, instead of measuring the spectra of the dispersed chitosan-dye complex, the solution is centrifuged for the sedimentation of the colloids, and the concentration of the uncomplexed dye in the supernatant is measured. By performing this simple procedure, sensitivity can be improved to >2 ppm. Equilibration time did not influence the measurements. Charge measurements and bathochromic shift of the measured spectra might yield information about the mechanism of the interaction between the dye and the polymer.
Asaf Mendelovits, Tami Prat, Yotam Gonen, and Giora Rytwo, "Improved Colorimetric Determination of Chitosan Concentrations by Dye Binding," Appl. Spectrosc. 66, 979-982 (2012)