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This article in SSSAJ

  1. Vol. 33 No. 5, p. 665-667
    Received: Feb 21, 1969
    Accepted: Apr 21, 1969

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Evaluating the Use of Na+, Ca2+, and Divalent Cation Electrodes in Some Soil Extracting Solutions1

  1. S. A. El-Swaify and
  2. M. N. Gazdar2



The performances of sodium activity, calcium activity, and divalent cation activity electrodes were determined and compared with predicted theoretical responses in unbuffered systems and in buffered systems at concentrations of 0.2 m, 0.5 m, and 1.0 m. In support of previous findings on a less selective sodium electrode, results show that the Na-electrode exhibits a response which is nearly Nernstian, allowing good estimates of Na+ ion activities in soil extracts. In contrast, the usefulness of the calcium and divalent-electrodes in buffered systems (and subsequent usefulness for determining exchangeable ions) was found to be limited particularly at high levels of total salt concentration. Although better response was observed for these two electrodes in unbuffered systems, the determination of Ca2+ and Mg2+ in water-soil extracts by their combined use is limited by the apparent reversibility of the calcium electrode to Mg2+ ions present in calcium-magnesium salt mixtures.

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