| The extraction characteristics of trivalent lanthanides by three crown ether carboxylic acids of different lipophilicities were investigated. Extraction was found to be independent of anions and strongly dependent on pH. Quantitative extraction of lanthanides was observed in the pH range of 6-8 by all three crown ether carboxylic acids: sym-dibenzo-16-crown-5 oxyacetic acid (I), 2-(sym-dibenzo-16-crown-5-oxy)hexanoic acid (II), and 2-(sym-dibenzo-16-crown-5-oxy)stearic acid (III). Results of competitive experiments indicated that this extraction system was highly selective for lanthanides relative to other major ionic species, such as the alkali metal ions, the alkaline earth metal ions, and transition metal ions. The distribution coefficients of lanthanides were at least two orders of magnitude greater than that of sodium, which has about the same ionic radius as the trivalent lanthanide ions. The crown ether carboxylic acids also showed significant selectivities among different lanthanides. For example, the relative distribution of Lu;The extraction method has been applied to the determination of low levels of lanthanides in natural waters and in biological materials. Sym-dibenzo-16-crown-5-oxyacetic acid had insufficient lipophilicity to remain in the organic phase when the pH of the aqueous phase was high and the organic to aqueous phase ratio was small. Extraction efficiency increased with the increasing lipophilicity of the crown ether carboxylic acids, which followed the order I ;Proton-driven cation transport against the cation concentration gradient was studied using bulk liquid membranes and emulsion liquid membranes containing crown ether carboxylic acids. Both membrane systems acted as efficient lanthanide ion pumps. The rate of transport of lanthanides was found to decrease slightly from Lu;Uranium can also be extracted by the three crown ether carboxylic acids with high efficiency. 2-(Sym-dibenzo-16-crown-5-oxy)hexanoic acid was utilized to extract uranyl ions from seawater and river water samples into chloroform, followed by back-extraction with a pH 2 nitric acid solution prior to NAA. The extraction method combined with NAA provides a sensitive method for the determination of uranium in natural waters. |
