Masking effects on conductimetric titration of lewis acid with EDTA in dimethylformamide

Abstract

This paper discusses the masking action on conductimetric titration of metal chloride with EDTA in DMF. It has been previously reported that several inflection points were observed in conductimetric titration of Lewis acids with EDTA in DMF as a result of chelating and replacement reaction. Then, it was investigated to mask and to decrease the number of inflection points by the addition of proper masking agents. Ammonium perchlorate, oxalic acid, nitric acid and lithium nitrate were used as the above masking agents. In the case of cupper(II), nikel(II) and cobalt(II) the inflection points due to replacement reaction (metal:EDTA=2:1) was disappeared by the addition of the above agents, while the other inflection point corresponding to chelating reaction (metal:EDTA=1:1) was obtained. However, magnesium and strontium chloride titration curves could not be simplified. Proper ratios of additives to metal ions were as follows; 1:1 for nitric acid or lithium nitrate and 1:2 for oxalic acid. Differential titration of mixed solution of metal chlorides which were masked or unmasked by the above agents was carried out and gave satisfatory results. Less than 10% of water gave no influence on the results. © 1977, The Japan Society for Analytical Chemistry. All rights reserved.