Jiří Adam

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.

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.

Extractions with long-chain amines-VIII Colorimetric determination of chromium(VI) with diphenylcarbazide.

Traces of chromium(VI) are extracted from sulphuric acid solution into a chloroform solution of trioctylmethylammonium chloride. After the addition of solid diphenylcarbazide to the separated organic phase, a red colour is developed and is measured spectrophotometrically at 550 nm. A great number of common metals, including iron and copper, do not interfere when present in ratios up to at least 1:40,000 (chromium: metal).

Determination of thorium and scandium by indirect chronopotentiometric stripping analysis.

A highly sensitive chronopotentiometric determination of thorium or of scandium is described. It is based on the substitution of thorium or scandium for lead (or zinc) in the lead-EDTA complex, and measurement of the liberated lead by deposition on a mercury film electrode, followed by a chemical oxidation stripping process during which the potential of the mercury electrode is monitored. Thorium has been determined at concentrations in the range 10(-5)-10(-7)M by use of deposition times from 1 min to 1 hr.

Extraction of some metal phenylacetates into chloroform.

Phenylacetic acid has been found to be very useful as a reagent in the extraction of large quantities of certain ions, notable iron(III), cobalt(II), copper(II), lead, zinc, cadmium and uranyl. A 1M solution of the reagent in chloroform is used to extract up to 200 mg of certain ions from small volumes of aqueous phase. Selectivity is increased by pH control and masking.

Extractions with long-chain amines—III: Colorimetric determination of molybdenum as thioglycollate

A highly selective and sensitive colorimetric determination of molybdenum(VI) based on its extraction with a chloroform solution of trioctylamine from solutions of acetic and thioglycollic acid (TGA) is described. The yellow chloroform extract containing the molybdenum-TGA complex is measured at 370 nm. With a single extraction it is possible to determine small amounts of molybdenum in the presence of very large concentrations of almost all metals. Only bismuth, mercury and tungsten interfere.

Extraction with long-chain amines—IV: Separation and colorimetric determination of gold

A highly selective method, almost free from interferences, for extraction of gold(III) from sulphuric acid into a chloroform solution of trioctylamine (TOA) is described. The yellow extract is then measured at 325-330 nm. Gold can be determined in the presence of platinum. The method has been applied to the determination of gold in waste dumps. A more sensitive method is based on reaction of the gold with diphenylcarbazide after the separation of the gold from the TOA-chloroform extract. The violet colour is stable and is measured at 560 nm.

Colorimetric determination of thorium with Methylthymol Blue

Thorium forms with Methylthymol Blue (MTB) in alkaline medium (pH 9-10) a complex of the composition Th(MTB)(2), even in the presence of EDTA, which masks almost all metals against the reagent. This can be used for selective determination of traces of thorium (0.5-2.8 ppm) by measurement of the absorbance at 535 nm.

Contributions to the basic problems of complexometry—XXVI determination of calcium in the presence of large amounts of magnesium

Two methods for the determination of calcium in the presence of very large amounts of magnesium are proposed. Both are based on back-titration of excess of EGTA, Thymolphthalexone being used as indicator. In the one method the titrant is a zinc solution, in the other a calcium solution is used, with a small amount of zinc present for end-point indication. Both titrations can be performed either visually or spectrophotometrically.

Extraction with long-chain amines-VIII Extraction of the chromium-DCTA complex and its colorimetric determination.

Chromium(III) is extracted as the DCTA complex by ion-association with trioctylmethylammonium chloride (Aliquat 336-S), into chloroform, and stripped into 1M potassium nitrate for spectrophotometric measurement at 540 nm. Iron(III) copper(II) are removed beforehand by extraction whith phenylacetic acid. High concentrations of nickel or cobalt prevent complete extraction.