Ligand competition

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Sunda and Hanson [247] have used ligand competition techniques for the analysis of free copper (II) in seawater. This work demonstrated that only 0.02 -2% of dissolved copper (II) is accounted for by inorganic species. (i.e., Cu2+, CuC03, Cu(OH)+, CuCl+, etc.) the remainder is associated with organic complexes. Clearly, the speciation of copper (II) in seawater is markedly different from that in fresh water. 

Prior to the introduction of ion-selective electrode techniques, in situ monitoring of free copper (II) in seawater was not possible due to the practical limitations of existing techniques (e.g., ligand competition and bacterial reactions). Ex situ analysis of free copper (II) is prone to experimental error, as the removal of seawater from the ocean can lead to speciation of copper (II). Potentially, a copper (II) ion electrode is capable of rapid in situ monitoring of environmental free copper (II). Unfortunately, copper (II) has not been used widely for the analysis of seawater due to chloride interference that is alleged to render the copper nonfunctional in this matrix [288]. 

To determine down to 6 ppt of lead in seawater Wu and Batley [404] used absorptive stripping voltammetry with ligand competition using xylenol orange. 

Walker, F.A. and Benson, M., Entropy, enthalpy, and side arm porphyrins. 1. Thermodynamics of axial ligand competition between 3-picoline and a series of 3-pyridyl ligands covalently attached to zinc tetraphenylporphyrin. J. Am. Chem. Soc., 1980, 102, 5530-5538. 

Scarano, G., Bramanti, E. and Zirino, A. (1992) Determination of copper complexation in sea water by a ligand competition technique with voltammetric measurement of the labile metal fraction. Anal. Chim. Acta, 264, 153-162. 

Seeman P, Sunahara RK, Niznik HB (1994) Receptor-receptor link in membranes revealed by ligand competition Example for dopamine Di and D2 receptors. Synapse 77 62-64. 

Sunda W. G. and Hanson A. K. (1987) Measurement of free cupric ion concentration in seawater by a ligand competition technique involving copper sorption onto Cl8 SEP-PAK cartridges. Limnol. Oceanogr. 32, 537-551. 

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