TY - JOUR
T1 - Complexation of Cu(II) with a soil humic acid
T2 - Response characteristics of the Cu(II) ion-selective electrode and ligand concentration effects
AU - Fitch, Alanah
AU - Stevenson, F. J.
AU - Chen, Y.
PY - 1986
Y1 - 1986
N2 - A study was made of parameters affecting the binding of Cu(II) to a soil humic acid, using the Cu(II) ion-selective electrode (ISE). A concentration effect was observed, both in estimates for total Cu(II) bound (maximum binding capacity) and apparent stability constant for binding at the strongest site (K1*). Log K1* values (pH 4, ionic strenth of 0.005) ranged from 6.3 at a humic acid concentration of 0.06 mg/ml to 7.0 at a concentration of 0.25 mg/ml. A still higher value (8.2) was obtained using an approach that permitted measurements to be made at low concentrations of the metal ion (pCu 8). An evaluation of the Cu(II) ISE revelaed that the electrode exhibited Nernstian response in the presence of humic acid, and that extension of the linear portion of the ISE standard curve to lower free Cu(II) concentrations (i.e. pCu 6 to near pCu 8) could be used for estimating free and bound forms of Cu(II). Extrapolation to the lower values permits study of the binding of Cu(II) to the stronger sites, a factor of some importance to natural systems where percent saturation of organic material is expected to be low.
AB - A study was made of parameters affecting the binding of Cu(II) to a soil humic acid, using the Cu(II) ion-selective electrode (ISE). A concentration effect was observed, both in estimates for total Cu(II) bound (maximum binding capacity) and apparent stability constant for binding at the strongest site (K1*). Log K1* values (pH 4, ionic strenth of 0.005) ranged from 6.3 at a humic acid concentration of 0.06 mg/ml to 7.0 at a concentration of 0.25 mg/ml. A still higher value (8.2) was obtained using an approach that permitted measurements to be made at low concentrations of the metal ion (pCu 8). An evaluation of the Cu(II) ISE revelaed that the electrode exhibited Nernstian response in the presence of humic acid, and that extension of the linear portion of the ISE standard curve to lower free Cu(II) concentrations (i.e. pCu 6 to near pCu 8) could be used for estimating free and bound forms of Cu(II). Extrapolation to the lower values permits study of the binding of Cu(II) to the stronger sites, a factor of some importance to natural systems where percent saturation of organic material is expected to be low.
KW - Langmuir equation
KW - metal-organic complexes
KW - potentiometric titration
KW - Scatchard plot
KW - soil organic matter chemistry
UR - http://www.scopus.com/inward/record.url?scp=0001035789&partnerID=8YFLogxK
U2 - 10.1016/0146-6380(86)90100-2
DO - 10.1016/0146-6380(86)90100-2
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AN - SCOPUS:0001035789
SN - 0146-6380
VL - 9
SP - 109
EP - 116
JO - Organic Geochemistry
JF - Organic Geochemistry
IS - 3
ER -