Effect of ethanol in the organic phase on liquid-liquid extraction in monosegmented flow analysis. Determination of zinc in drugs

摘要

In liquid-liquid extraction performed by monosegmented flow analysis (MSFA), the aqueous sample is introduced between two air bubbles and flows, under restricted dispersion, through a glass extraction tube where the analyte is retained, usually at pH higher than 8. The retained analyte is removed to a small volume of an organic phase containing a ligand which is introduced after the second air bubble. In this work, the effect of the organic phase composition on the extraction of Cu(II), Zn(II) and Cd(II) in MSFA systems was investigated by changing the ethanol content )0.1-4% v/v) in toluene, chloroform and carbon tetrachloride. The extracting effeciency of the organic phase containing ethanol was evaluated by using dithizone (DT), 1-2-pyridyalzo-2 naphthol (PAN) and sodium diethyldithiocarbamate (DDTC) as ligands for the metals. The MSFA extraction system was improved by introducing a new syringe-based device for organic phase delivery. The presence of ethanol in the organic phase shown a remarkable (up to ten times) effect on the extraction efficiency of the flow system when DT is employed. Its presence is mandatory if DDTC is used, as it accounts for ligand solubility in organic phase. The extraction efficiency also increases with the pH of the aqueous phase as a consequence of higher ionisation of the silanols, where the analytes are adsorbed before extraction.T he system has been evaluated for determination of Zn(II) in drugs showing results. Typical sample frequency, sample and organic phase consumption are 30 samples per hour, 200 and 100 #mu#l respectively.