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This article in SSSAJ

  1. Vol. 51 No. 4, p. 924-929
     
    Received: Nov 17, 1986


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doi:10.2136/sssaj1987.03615995005100040018x

Interference of Humic Substances on Chloride Analysis Using the Chloride Ion-selective Electrode1

  1. F. J. Sikora and
  2. F. J. Stevenson2

Abstract

Abstract

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).

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