バナジン酸およびヘキサメチレンテトラミンによる希土類元素の間接定量法

概要

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As it was found that rare earth elements formed a precipitate stoichiometrically combining with vanadic acid and hexamethylenetetramine, an indirect determination of rare earths was made by the estimation of vanadium in the precipitate. The composition of the precipitate was considered to be M(VO3)3·8HVO3·2Hexa·4H2O, where M=rare earth elements and Hexa=hexamethylenetetramine. The pH for complete precipitation was 35 for Pr, La and Nd, and 45 for Sm whereas the precipitation of Ce was incomplete. The recommended method is as follows. The solution containing rare earth elements is adjusted to pH4.5 with acetic acid-ammonium acetate and ammonium vanadate about 20moles equivalent against the rare earths is added. After an addition of 10ml of 2% hexamethylenetetramine with stirring, the precipitate was separated and washed with a solution of pH4.5 containing hexamethylenetetramine. It is dissolved in sulfuric acid and the solution is titrated with standard ferrous sulfate using diphenylamine as an indicator. Above 1mg of rare earth element was successfully determined.