Analytical Sciences

Abstract − Analytical Sciences, 19(8), 1133 (2003).

Interaction between SulfonephthaleinDyes and Chitosan in Aqueous Solution and Its Application to theDetermination of Surfactants
Koichi YAMAMOTO and KanaADACHI
Department of Materials Science, YonagoNational College of Technology, 4448, Hikona, Yonago, Tottori 683-8502,Japan
A spectrophotometric method for thedetermination of ionic surfactants with Bromophenol Blue (BPB) based onincorporation into a precipitated chitosan was studied. Cationicsurfactants (CS+), such as a quaternary ammonium ion containinga long-chain alkyl group, associate with BPB2- buffered at aboutpH 9 to form the ion associate(CS+)2·BPB2-. CS+associates with anionic surfactants (AS-). In the presence of adefinite amount of CS+, an increase in the amount ofAS- leads to a decrease in the amount of excess CS+,and therefore to a decrease in the amount of the ion associate ofCS+ with BPB2-. The addition of a chitosan dissolvedin acetic acid to a solution containing these ion associates leadsimmediately to precipitation of the chitosan and the incorporation of theion associates (CS+)2·BPB2- orCS+·AS- into the precipitated chitosan. Aftercentrifuging, ionic surfactants can be determined by the following twomethods: (1) the absorbance of the supernatant solution is measured at 590nm. (2) After the supernatant solution is separated, the precipitate isdissolved in an acetic acid solution and the absorbance is measured at 625nm. Because the color of the precipitate is judged by the naked eye, thiscan be applied to the visual method. This is a simple and rapid method forthe determination of a 10-6 M order of ionicsurfactants.