Rudolf Přibil

Contributions to the basic problems of complexometry-XII: Successive determination of thorium, rare earths and some other elements

Abstract The successive determination of thorium and rare earths with diethylenetriaminepenta-acetic acid (DTPA) and triethylenetri-aminehexa-acetic acid (TTHA) is described. Such a determination cannot be carried out with the commonly used EDTA or diamino-cyclohexanetetraacetic acid (DCTA). By combined titrations with DTPA and TTHA it is possible to determine successively not only thorium and rare earths, but also some bivalent elements which might be present in the material to be analysed.

Extraction with long-chain amines—II: Extraction and colorimetric determination of chromate

Highly selective extraction of chromate from slightly acidic solutions (0.1-0.2M sulphuric acid) with a chloroform solution of trioctylamine (Alamine 336-S) or trioctylmethylammonium chloride Aliquat 336-S) is described. Many metals such as iron, nickel, cobalt, copper, alluminium, zinc, are not extracted, even if present in large concentrations. Coextraction of vanadium(V) and uranium(VI) is prevented by addition of sodium chloride. Traces of extracted molybdenum are scrubbed with ammonium oxalate. Final determination of chromium is based on measurement of the absorbance of the extract at 445-450 nm.

New redox systems—II: Oxidation of cobaltII with ironIII chloride in 1:10-phenanthroline solutions

Abstract The oxidation of cobaltII with ironIII, in the presence of 1:10-phenanthroline, has been studied both potentiometrically and colorimetrically. From these studies it can be deduced that the course of the reaction is [Fe2(Phen)4(OH)2]4+ + 2Co(Phen)32+ + 2HPhen+ ⇌ 2Fe(Phen)32+ + 2Co(Phen)33+ + 2H2O (1) Conditions have been found in which the reaction proceeds quantitatively. Its utilisation in both macro and micro determination of cobalt is discussed.

COLORIMETRIC DETERMINATION OF VANADIUM WITH XYLENOL ORANGE

Abstract A highly selective colorimetric method for vanadium V , based on its colour reaction with Xylenol Orange, is described. In the presence of 1,2-diaminocyclohexanetetra-acetic acid (DCTA) this method is almost specific for vanadium, because other elements are screened, and do not interfere in moderate amounts.

PRESENT STATE OF COMPLEXOMETRY. IV. DETERMINATION OF RARE EARTHS.

A review of the visual complexometric determination of the rare earths, scandium and yttrium with various volumetric reagents is presented. As in previous parts attention is paid to the complexometric behaviour of these metals and to the problems of interferences in their determinations. Methods for the determination of thorium, scandium and some rare earths in mixtures are described in detail. Recent developments and further possibilities in this field are discussed.

Contributions to the basic problems of complexometry-IX: The determination and masking of aluminium

Abstract It has been found that aluminium forms complexes with 1,2-diaminocyclohexane tetraacetic acid(CDTA)almost instantaneously, even at room temperature and m the presence of large excess of neutral salts. Contrary to general opinion, it is also possible to mask aluminium with ammonium fluoride at room temperature. If further determinations are being made with EDTA, a concentration of fluoride equivalent to the molar ratio 1:5 to 1:6 is sufficient for screening of aluminium. If the determinations are with CDTA it is necessary to add 30–50% excess of fluoride, corresponding to the molar ratio Al:F = 1:6. These findings has been utilised to develop a very simple and accurate method for the determination of aluminium and iron in their mixtures. Both determinations are based on the back-titration of an excess of EDTA with lead nitrate using Xylenol Orange as indicator. The further possibility of the determination of tervalent chromium, titanium and manganese in the presence of aluminium and iron has been discussed.

Contributions to the basic problems of complexometry—I: The blocking of indicators and its elimination

Abstract The formation with metallochromic indicators of complexes inert to substitution makes certain complexometric titrations impossible. The cations of bivalent copper, cobalt and nickel, in addition to others, show a tendency to form such complexes with for example Eriochrome Black T, Xylenol Orange, Methylthymol Blue. It has been proved that small quantities of o -phenanthroline entirely suppress this phenomenon, which is undesirable in complexometry. The presence of o -phenanthroline makes it possible reliably to determine copper as well as cobalt complexometrically against Xylenol Orange even at room temperature. The influence of o -phenanthroline is explained by the formation of substitution-labile complexes with copper or cobalt, and by the reaction mechanism at the point of equivalence. The influence of other materials on the colour change of the indicator in these titrations is also discussed.

Analytical use of the selective extraction of copper as its phenylacetate

Chloroform solution of phenylacetic add has been found very suitable for extraction and colorimetric determination of copper. Iron and uranium are the main interferences, which can be overcome by masking with ammonium fluoridc. Under these conditions, only gold(III), platinum(IV) and palladium(II) are co-extracted, but their colour does not interfere with measurement of the green copper extract at 700 nm. The method has been applied to the determination of copper in iron, steels, uranium, lead concentrates and alloys containing nickel, cobalt, etc. The extraction procedure can also be used to remove interference of iron, copper and uranium in the determination of manganese with formaldoxime.

Extraction with long-chain amines—V: Colorimetric determination of cobalt with nitroso-R salt

The colorimetric determination of cobalt with nitroso-R salt (NRS) has been modified and improved by the introduction of extraction of the Co-NRS chelate into a chloroform solution of trioctylmethylammonium chloride. Ammonium phosphate, fluoride and mainly citrate were used for masking iron, nickel, copper and calcium, which under the described conditions do not interfere even in 2000-fold excess. The method is very sensitive and permits determination of about 1 mug of cobalt per ml of the extractant.

1-Hydroxy-ethylidene-1,1-diphosphonic acid as a titrimetric agent.

1-Hydroxy-ethylidene-1,1-diphosphonic acid (HEDPHA) has been proposed as a highly selective titrimetric reagent for thorium. In the presence of 1,2-diaminocyelohexanetetra-acetic acid (DCTA) a soluble binuclear ternary complex, Th(2)(DCTA)(2)(HEDPHA), is formed. The determination of thorium is carried out in a slightly acidic medium, buffered with urotropine, with 0.025M HEDPHA, and Xylenol Orange as indicator. DCTA masks all bivalent metals, rare earths, scandium, yttrium, bismuth, iron, gallium and indium. Only zirconium, titanium, aluminium and large amounts of thallium(III) interfere.