Mechanized method for measuring metal partition in n-octanol–aqueous systems. Partition of aluminium complexes

Abstract

We have established a system combining a continuous-flow extraction system with an electrothermal atomic absorption spectrometer to evaluate the lipophilicity of metal complexes. Quantitative data are obtained by determining the conditional partition constants (D′) of such metal complexes between n-octanol and water. Extraction equilibrium is obtained in a liquid–liquid segmented flow. After extraction a fraction of pure n-octanol phase is separated with either a membrane or a non-membrane separator. Via a simple interface, the n-octanol extract is introduced into the graphite tube. The D′ value is evaluated from the ratio of the concentration of metal in n-octanol to that in aqueous solution. Good repeatability (s_r approximately 3.5%, n= 10) is obtained both for standard solutions and for normal extracts from the continuous-flow extraction system. A D′ value as low as 3 × 10^–5 can be determined by the present system. The precision, measured as the s_r of the mean, is better than 10%. The sample throughput, using at least three injections per sample, is about three samples h^–1. The system has been used for studying the partition of aluminium–citrate (AlCit) complexes to n-octanol. AlCit, the only aluminium–citrate species partitioning, was found to have a D′ value of 0.49 × 10^–3. Further, conditional constants for aluminium in supernatants from rat feed slurries obtained from in vitro studies of gastro-intestinal absorption have been measured.