Über fokussierenden Ionenaustausch VII. Quantitative Mikroanalyse von Schwermetallen und seltenen Erden

1 Focusing ion exchange as a method of separation of metal‐ions, taking place in homogeneous solution in the presence of a complex‐formation‐ and an electrical potential‐gradient, is again confronted with heterogeneous ion‐exchange and ionophoresis and the distinctions are stressed. 2 The phenomenon of “double‐focusing”, meaning the stationary existence of two lines of the same metal in the presence of two complexing agents (one of which is an amino‐poly‐acetic acid), offers a possibility for the estimation of μg‐ and ng‐amounts of various metals, incl. Fe 3+ , Cu 2+ , Pb 2+ , Co 2+ , Y 3+ , and heavy rare earths. This can not be realized with ordinary ion‐exchange nor electrophoresis. 3 One of the lines of a double‐focus, being located on the acid side of a pH‐gradient, changes its intensity proportionally to the added amount of a chelating agent (NTA, EDTA, Chel CD). Macro‐chelatometry, using external indicators, direct and substitution titrations of metal‐traces on a filter‐paper strip, are described. The method is more accurate than various micro‐chemical procedures. 4 A phenomenological treatment of double‐focusing is given.