�ber die Ausschaltung gr��erer Eisenmengen bei komplexometrischen Titrationen

Determination of Cadmium in Zinc Concentrates and Other Zinc-Rich Materials. Anion Exchange

“…The color change is sharp from purple to blue. In the presence of traces of impurity metalse.g., copper or iron-which might block the action of the Eriochrome Black T indicator, preliminary complexing with cyanide and subsequent liberating with formaldehyde or chloral hydrate may be employed (2,9). Traces of iron can be reduced with ascorbic acid and masked as ferrocyanide (2).…”

“…In the presence of traces of impurity metalse.g., copper or iron-which might block the action of the Eriochrome Black T indicator, preliminary complexing with cyanide and subsequent liberating with formaldehyde or chloral hydrate may be employed (2,9). Traces of iron can be reduced with ascorbic acid and masked as ferrocyanide (2). It should be emphasized, however, that in the work described above these added manipulations were not required because of the effectiveness of the iodide elution step.…”

Micro-EDTA Titration of Calcium. Magnesium Interference

“…The chief difficulties in applying these dyes to the determination of free metal ion concentrations in body fluids are the dependence of the reactions upon pH, necessitating the handling of biological samples without exposure to air, and the interference caused by traces of heavy metals, for which both dyes have great affinity (1)(2)(3)(4)(5)(6)(7)(8).…”

“…However, it is not advisable to use reducing agents in this connection. Although ascorbic acid (3,8) and hydroxylamine hydrochloric acid (8) aid the masking of iron and the heavy metals, manganese, if present, will be reduced. In this case it is not masked by the triethanolamine and will be titrated by the EDTA, resulting in too high calcium recoveries.…”