Transport of lipophilic metal complexes through permeation liquid membrane, in relation to natural water analysis: Cu(II)–8-hydroxyquinoline complex as a model compound

Lipophilic metal complexes are potentially toxic or bioavailable. These complexes may be present in natural waters but, due to lack of sensitive methods for their detection, their contribution to biouptake is poorly understood. Hence, an analytical technique, based on permeation liquid membrane (or supported liquid membrane) (PLM or SLM) has been investigated for the determination of lipophilic metal complexes. For this purpose, key parameters, such as the nature of solvent, diffusion coefficient in the membrane, Dm, partition coefficient between the solution and the membrane, Kp, and permeability coefficient, P, governing the transport of Cu(II)–8-hydroxyquinolinate (image) through a flat sheet PLM comprising toluene/phenylhexane have been evaluated. image was chosen as model lipophilic complex. Copper–8-hydroxyquinolinate is used as a pesticide and may be present in natural waters. The effects of pH, in the range 6–8, and the membrane thickness on the image transport were also studied. The results showed that the neutral species is transported efficiently across the membrane containing toluene/phenylhexane mixture. Values of Dm = 3.0 × 10−7 cm2 s−1 and P = 1.45 × 10−3 cm s−1 were found; P is independent of pH in the studied pH range. The partition coefficient, Kp, of image in phenylhexane/toluene mixture was also determined using the classical liquid/liquid extraction method for comparison. The application of PLM method was tested for the trace level determination of lipophilic complexes using hollow fibre permeation liquid membrane to preconcentrate the analyte. High preconcentration factor for image was achieved using the designed HFPLM device. Finally, the applicability of this method to image was tested in a real water sample by spiking it with 8-hydroxyquinoline (10 μmol L−1). The results showed a quantitative recovery. The theoretically estimated LOD is few pmol L−1.