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Photometric microtitrations. VII. Chelatometric determination of scandium and lanthanides by direct and successive titration using Methylxylenol Blue

S. Kotrlý, V. Mach, and K. Vytřas

Department of Analytical Chemistry, University of Chemical Technology\ 532 10 Pardubice


Abstract: The precision and accuracy attainable in direct titrns. of Sc3+, La3+ or Er3+ with 0.001M EDTA di-Na salt (I) by using Methylxylenol Blue as a metallochromic indicator was studied. For linear extrapolation of the endpoint in titrns. of Sc3+ and Er3+ with I it is convenient to measure the titrn. curve at 560 nm (in case of La3+ at 570 nm) and to adjust the concn. of indicator in the titrated soln. to 1-2 × 10-5M. For the microtitration of Sc3+, the pH range 2-3 is obtained by adding chloroacetate buffer while for the titrn. of lanthanides the optimum pH value (pH 5.4 for Er3+ and pH 5.9 for La3+) is adjusted with hexamethylenetetramine buffer. The influence of the blank titrn. on accuracy of results was eliminated by successive titrn.: the analyzed soln. was measured and introduced into a soln. immediately after completing a preliminary titrn. of the ion being detd. In repeated detns. of these metals in very dil. solns. (cM ∼10-5M) the relative random error is ≤1% and the systematic error is 0.8-1.5% (referred to the most accurate visual titrn. performed at concns. higher at least by 1 numerical order). Accurate results can also be achieved by a successive titrn. Sc3+ is titrated at pH 2.5; then the pH value is adjusted to 5.4-5.9 by adding hexamethylenetetramine buffer and La3+ (or Er3+) is titrated.

Full paper in Portable Document Format: 334a499.pdf


Chemical Papers 33 (4) 499–506 (1979)

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