Partition of copper and cadmium between n-octanol and aqueous phases using segmented flow extraction

The hyphenation of continuous-flow extraction with electrothermal atomic absorption spectrometry as a means for studies of the partition of metal complexes between n-octanol and water has been further mechanised. It is now possible to separate cleanly either the n-octanol or the aqueous phase after equilibration and measure their metal concentrations sequentially by the electrothermal atomic absorption spectrometer. The mechanised method can therefore now exclude the effects of flow variations and precipitation or absorption of metal in the system. The repeatability of the metal determinations by the complete system is good. In most cases, RSDs below 5% were obtained for determinations in either n-octanol or water. The precision of an evaluated conditional partition constant, measured as the standard deviation (SD) of the mean log D′ value, is better than 0.1. The time needed for one determination is about 20 min. Quantitative partition data were obtained using this system by determining the conditional partition constants (D′) for Cd and Cu complexes with diethyldithiocarbamate and humic/fulvic acids. Uncharged metal complexes with diethyl dithiocarbamate are hydrophobic and complex formation thus increases sharply the hydrophobicity of the metals. Humic/fulvic acids have hydrophillic parts not taking part in complexation and their complexes with Cd and Cu are therefore still hydrophillic. The direct uptake of Cd and Cu via lipid–soluble complexes with humic/fulvic acids is therefore hardly significant.