Contributions to the basic problems of complexometry-XXV Determination of rare earths and phosphate without separation.
A new method for coraplexometric determination of rare earths (RE) and phosphate without prior separation is described. It is based on indirect determination of RE by back-titration of an excess of DTPA with zinc solution, with Xylenol Orange as indicator. After the titration an excess of La-EDTA complex solution is added and the solution is titrated again with zinc at 40-50 degrees . During this titration lanthanum is displaced from its complex and precipitated as phosphate: LaY(-) + Zn(2+)+ PO(4)(3-) = LaPO(4) + ZnY(2-). The consumption of zinc solution corresponds to the amount of phosphate.
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J. Heyrovský Institute of Physical Chemistry and Electrochemistry, Czechoslovak Academy of Sciences, Prague 1, Jilská 16, Czechoslovakia.