Complexation capacity

Influence of U colloidal transport in organic-poor surface waters has been far less studied. Riotte et al. (2003) reported U losses from 0 to 70% during ultrafiltration experiments for surface waters of Mount Cameroon without nearly any DOC. Even in the low concentration waters, U can be significantly fractionated from other soluble elements by the occurrence of a colloidal phase, probably inorganic in origin. However, such fractionations are not systematic because of the occurrence of various colloidal phases, characterised by different physical and chemical properties, and hence different sorption and/or complexation capacities (Section 2.1). 

Wood et al. [303] have described an ion exchange technique for the measurement of the copper complexing capacity of seawater samples taken in the... 

Because of this complexation capacity, any standard addition performed at high pH will not return 100% of the spike, so a true value for the copper concentration cannot be calculated. Therefore, after an initial measurement at high pH the sample was acidified to pH 1.0 with 0.5 ml acid and another trace obtained. This compared the amount of copper released at low pH with the labile fraction at high pH. Standard additions were performed on the sample at low pH so almost all of the spike was returned. This allowed an estimate to be made of the percentage of total copper that was labile at high pH, and the quantification of this fraction in pg/1. This is illustrated graphically in Fig. 5.9. 

North Sea water at the natural pH has a complexing capacity, probably due to the presence of dissolved organic compounds, in a concentration equivalent to 0.3 M copper. The complexing capacity is zero at pH 2.7. The method of standard addition for the determination of electroactive copper and lead concentrations may lead to erroneous results in samples where complexation of this type occurs. 

A kind of standard additions approach can also be used for the measurement of apparent complexing capacity. In this technique, labile copper is measured by differential pulse anodic stripping voltammetry after each of a number of spikes of ionic copper have been added to the sample [420]. 

The 1,3-dipolar cycloaddition of nitrones to vinyl ethers is accelerated by Ti(IV) species. The efficiency of the catalyst depends on its complexation capacity. The use of Ti( PrO)2Cl2 favors the formation of trans cycloadducts, presumably, via an endo bidentate complex, in which the metal atom is simultaneously coordinated to the vinyl ether and to the cyclic nitrone or to the Z-isomer of the acyclic nitrones (800a). Highly diastereo- and enantioselective 1,3-dipolar cycloaddition reactions of nitrones with alkenes, catalyzed by chiral polybi-naphtyl Lewis acids, have been developed. Isoxazolidines with up to 99% ee were obtained. The chiral polymer ligand influences the stereoselectivity to the same extent as its monomeric version, but has the advantage of easy recovery and reuse (800b). 

The SBE derivative was chosen for development as a new excipient, because the material demonstrated high water solubility and excellent complexation capacity relatively unaffected by the substitution level, and the raw materials were reasonably available for commercial scale manufacturing. The only remaining decision was the level of substitution to introduce. 

The complexing capacity of hydroxamic acids was predicted by Werner in 1908, who also indicated the metals most likely to form stable complexes.288 Since then, the formation of poorly soluble and intensely coloured hydroxamates has been used for analytical determinations for a number of metal ions, such as Fe3+, Mos+, Vs+ etc. A recent general review of transition metal complexes of hydroxamic adds included the few known examples of silver(I) complexes.289... 

To illustrate one type of speciation research, i.e. the determination of the apparent complexation capacity for copper (CCqu) and the conditional stability constant (K1), examples are given for three marine areas, viz. the Scheldt estuary, the Southern Bight of the North Sea and the open north Atlantic Ocean. A hypothetical model is presented giving the complexation capacity across the land-sea boundery from river to ocean. 

Important complexation and/or sorption reactions between colloids and trace elements may occur. In studies on the interactions of copper with EDTA and Y AI2O3 as model-ligand and -particles, the apparent complexation capacity was increased by the addition of the particulates (Plavsic et al., 1980). This was also observed for the influence of MnC>2-colloids on the complexation capacity for lead (Sigg et al., 1984). 

In natural systems therefore part of the complexation capacity might be caused by colloidal material. This was demonstrated in experiments on the complexation capacity of samples from the Scheldt estuary at different salinities, determined as function of several concentration steps, using a hollow fiber ultrafiltration set up with a theoretical cut off of MW 5000 (Kramer and Duinker, 1984a). 

The CCcu appeared to be linearly dependent on the concentration factor only in the upper part of the estuary. No increase in the CCcu couW be observed after concentration at higher salinities. The riverine colloidal material apparently coagulates to particles and floes at increasing salinity in the upper part of the estuary. These floes are retained by the 0.45 ym filter, thus no longer contributing to the complexation capacity of the "dissolved" fraction. This explains the non conservative behaviour of the CCcu n this part of the estuary (see later). Samples taken from the north Atlantic Ocean did not show an increase in CCcu> even aftar a concentration factor 200 times. 

Complexation capacity and conditional stability constants in marine waters. 

CCcu and K determination by DPASV analysis. To illustrate the possibilities of speciation studies, an example of the application to natural waters will be presented in this section, with special reference to the determination of the complexation capacity for copper of marine waters. 

Complexation Capacity (CC), conditional stability constant (K1), temperature, pH, oxygen and suspended matter content in the river Scheldt estuary at different salinities. 

Fig. 2. Means of triplicate analysis of apparent Scheldt estuary copper complexation capacity in the river Scheldt estuary at various salinities.

Southern North Sea. Surface watersamples were collected in the southern part of the North Sea, in coastal waters and offshore in October 1982 (Fig. 3). In Table 6 the CCqu and log K are presented. It appears that coastal waters (stations 1 and 2) show a higher complexation capacity (82 nM Cu2+) then the samples with less contribution of river water (stations 3 and ft) with a CC u of ftft nM Cu2+, with an intermediate value for the station in the German Bight. 

Fig. 5. A) Apparent copper complexation capacity (CC U) in nM Cu2+ B) Conditional stability constants (K ) presented as log K. ...

Mean values of complexation capacity (CC), conditional stability constants (K1) and rate constants (kf ) for different area in north Atlantic waters. 

It seems from these figures that a positive relation exists between plankton abundance and the complexation capacity. Both exudates and intracellular fluids contain potential ligands, therefore no information on their relative contribution can be obtained from the CCcu- Differences in K however might be explained in terms of seasonal variations of plankton activity (Kramer, 1985). 

Fig. 7. Schematic model of the distribution of the apparent complexation capacity in river- and estuarine- (a), coastal- (b) and open ocean waters (c). The right part shows the situation L > M (based on Wood et al., 1983), the left part the hypothetical situation M > L for deep oceanic - (d) and estuarine waters (e). Bar graph shows the major sources for each system.

This is reflected in the complexation capacity. Usually a high organic matter content of river and estuarine waters will, together with the colloids in the "dissolved" fraction, result in a high CCqu (100 - 500 nM Cu2+), Fig. 7a. Coastal waters (Fig. 7b), as a result of mixing with seawater, have a lower CCcu (60 - 150 nM Cu2+). Open ocean surface waters of the North Atlantic have a CC u of 20 - 70 nM Cu2+, which in case of low in situ biological activity might be well below this value (Fig. 7c). 

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