Analytical Sciences

Determination of Polyhexamethylene Biguanide Hydrochloride Using Photometric Colloidal Titration with Crystal Violet as a Color Indicator

Takashi MASADOME,* Takaaki MIYANISHI,* Keita WATANABE,* Hiroshi UEDA,* and Toshiaki HATTORI**

*Department of Applied Chemistry, Faculty of Engineering, Shibaura Institute of Technology, Toyosu, Koto, Tokyo 135-8548, Japan
**Department of Electrical & Electronic Information Engineering, Toyohashi University of Technology, Toyohashi 441-8580, Japan

A solution of polyhexamethylene biguanide hydrochloride (PHMB-HCl) was titrated with a standard solution of potassium poly(vinyl sulfate) (PVSK) using crystal violet (CV) as an photometric indicator cation. The end point was detected by a sharp absorbance change due to an abrupt decrease in the concentration of CV. A linear relationship between the concentration of PHMB-HCl and the end-point volume of the titrant existed in the concentration range from 2 to 10 × 10⁻⁶ eq mol L⁻¹. Back-titration was based on adding an excess amount of PVSK to a sample solution containing CV, which was titrated with a standard solution of poly(diallyldimethylammonium chloride) (PDADMAC). The calibration curve of the PHMB-HCl concentration to the end point volume of the titrant was also linear in the concentration range from 2 to 8 × 10⁻⁶ eq mol L⁻¹. Both photometric titrations were applied to the determination of PHMB-HCl in a few contact-lens detergents. Back-titration showed a clear end point, but direct titration showed an unclear end point. The results of the back-titration of PHMB-HCl were compared with the content registered in its labels.

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