Interference of Humic Substances on Chloride Analysis Using the Chloride Ion-selective Electrode
- F. J. Sikora and
- F. J. Stevenson
Humic substances interfered with the ion-selective electrode determination of Cl- by complexing Ag+ and thereby reducing the activity of the potential determining ion. Binding of Ag+ was proven with a technique that involved equilibrium dialysis and Ag+ determination by atomic absorption spectroscopy. Competition between Ag+ and H+ for binding sites was evident from an increase in millivolt response of the Cl- ion-selective electrode with addition of HNO3 and release of protons upon Ag+ binding in the dialysis experiment. Selectivity coefficients (kCl,HA) for 11 humic and fulvic acids ranged from 0.59 × 10−4 to 1.3 × 10−4 mol g−1 at pH 6.5. Interference is negligible in solutions containing <0.1 g L−1 humic substances, but is serious in samples with low concentrations of Cl- (< 10−4.5 M) and high amounts of organic matter (>0.1 g L−1).Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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