Fig. 5. The E value of Cd in the calcareous soil as affected by pH and the presence of citric acid. The solid line represents the fitted five-parameter non-linear regression of E = 3.44 + 7.83/(1 + exp[-(pH-8.23)/-0.41]²¹: R² = 0.99, P < 0.0001. Hashed lines represent 95% confidence limits. The symbol () represents the mean E value of Cd, in the absence of ligands, measured with triplicate samples. The symbol (x) and error bars represent the mean value and standard deviation of triplicate measurements of (0.25–5 mM) concentrations of citric acid.

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