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Potentiometric determination of lead and copper ion activity in soil extracts

Potentiometrische bepaling van de lood en koper activiteit in bodemextracten

Synopsis

The applicability of ion selective electrode (ISE) potentiometry for the direct determination of the activity of free copper and lead ions in soil extracts was investigated in soil samples containing levels of total heavy metal levels near Dutch target values. For Cu-ISE and Pb-ISE, detection limits were found to be 0.1 micromol/l and 3 micromol/l, respectively, at a potassium nitrate concentration of 0.1 mol/l and pH=4. The detection limit increased at pH=2. The precision of the Cu-ISE was found to be better than the Pb-ISE in the range of about 0.1 micromol/l up to 1 millimol/l. Three soil samples were extracted with Milli-Q-water and 0.01 mol/l nitric acid. Total lead and copper concentrations in the extracts were found to be lower than the detection limit of the potentiometric method and, hence, direct detection of the activity of the free metals was not possible. From potentiometric titration curves of the Milli-Q-water extracts complexation capacities were estimated to be about a few micromol/l for both copper and lead. In addition, the potentiometric titration curves indicated similar physico-chemical behaviour of copper and lead in the same soil solution. Deviations in the shape of the potentiometric curve obtained for calibration samples were found for the sample with the higher pH, which might be due to interference of hydrolysed metal ions
 

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