Photometric Determination of Trace Amount of Mercury by the Ion Association System of Hg (Ⅱ)-Phen Anthroline and Congo Red

Mercury (Ⅱ) was reacted with 0.8 mL of 1.0×10-3mol·L-1 o-phenanthroline solution and 1.2 mL of 4.0×10-4mol·L-1 congo red in an HOAc-NaOAc buffer solution of pH 5.7 with addition of 0.8 mL of 10 g·L-1 gum arabic solution both as sensitizer and stabilizer, to form an ion-association complex. Linearity between values of absorbance and mass concentration of Hg (Ⅱ) was found in the range within 1.0 mg·L-1. Apparent molar absorptivity of the association complex found was 8.49×104L·mol-1·cm-1 at the wavelength of its absorption maximum, 540 nm. The proposed method was applied to the determination of mercury in samples of river water, giving RSD′s (n=5) less than 2.0% and average recovery of 100.4%.