Spectrophotometric Determination of Chlorhexidine Based on a Hydrophobic Interaction with the o-Hydroxyhydroquinonephthalein- Manganese(II) Complex1

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A simple spectrophotometric method has been established for the determination of chlorhexidine (CH) with the o- hydroxyhydroquinonephthalein(QP)-manganese(II) complex. The apparent molar absorptivity and relative standard deviation for 50.6μg of CH were 5.88×10⁴ 1mol^-1 cm^-1 and 0.47% (n=8), respectively. This method was applied to the determination of CH in a wide variety of pharmaceutical preparations with satisfactory analytical results. From the thermodynamic parameters (ΔG=-5.49kcal mol^-1, ΔH=0.04kcal mol^-1 and ΔS=18.60cal mol^-1 K^-1) obtained from a van′t Hoff plot, the binding between CH and the QP-manganese(II) complex was presumed to be a hydrophobic interaction.