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.     

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.     

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-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.     

Extraction with long-chain amines-X Complexometric determination of titanium after extraction of its ascorbate complexes

A highly selective extraction of titanium as its ascorbate complexes from slightly acidic medium into trioctylmethylammonium sulphate is described. After stripping into nitric acid, titanium is determined complexometrically. The method allows separation of titanium from large amounts of iron, aluminium and bivalent metals. The procedure for the determination of iron and aluminium after the titanium extraction is also given. The method has been applied to the determination of titanium in special alloys and minerals.     

Indirect complexometric determination of chromate

Chromate is determined indirectly, by precipitation as silver chromate, dissolution of the precipitate in potassium tetracyanonickelate, and titration of the liberated nickel with EDTA, with Murexide as indicator.     

Direct colorimetric determination of nickel with furildioxime

Summary An extractive method for the rapid colorimetric determination of nickel as the yellow furildioxime complex in chloroform is presented. The development of the method into one based on a single extraction without the need of preliminary separations, pH adjustment, and after-treatment of the extract has been made possible by buffering the aqueous phase, and masking interfering elements. The narrow range in alkalinity essential for quantitative extraction in the acetate-tartrate medium is maintained by the addition of borate. Interference from cobalt in 10-fold, and copper in 100-fold excess of nickel is eliminated by the use of thiosulphate and ethylene diamine as masking agents. Iron may be present in 2000-fold, manganese and titanium in 400-fold, chromium, molybdenum, palladium, tin, vanadium, zinc, and zirconium in 200-fold excess, making the method suitable for determination of nickel in quantities down to 0.5 g in rocks, steels, ores, and other materials.

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Direkte colorimetrische Bestimmung von Nickel mit Furildioxim

Zusammenfassung Das Verfahren beruht auf der Extraktion des gelben Nickel-Furildioxim-Komplexes mit Chloroform. Durch Pufferung der wäßrigen Phase und Maskierung von störenden Fremdionen kann die Bestimmung mit nur einer Extraktion durchgeführt werden, ohne Vortrennungen, pH-Einstellung und Nachbehandlung. Der enge Alkalitätsbereich, der für eine quantitative Extraktion im Acetat-Tartrat-Medium erforderlich ist, wird durch Zusatz von Borat gewährleistet. Störungen durch die 10fache Menge an Kobalt und die 100fache an Kupfer werden durch Thiosulfat und Äthylendiamin beseitigt. Eisen kann in 2000fachem, Mangan und Titan in 400fachem, Chrom, Molybdän, Palladium, Zinn, Vanadium, Zink und Zirkonium in 200fachem Überschuß zugegen sein. Das Verfahren eignet sich zur Nickelbestimmung bis herab zu 0,5 g in Gesteinen, Erzen, Stahl und anderen Materialien.

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The writer would like to express his sincere thanks to Prof. K. von Gehlen for furthering this work by making funds and laboratory facilities available, and to the Deutsche For schungsgemeinschaft for a grant to K. von Gehlen.     

Chromogenic silica nanoparticles for the colorimetric sensing of long-chain carboxylates

Silica nanoparticles functionalized with chromogenic spirobenzopyran and thiourea subunits show selective colour changes in the presence of certain long-chain carboxylates.     

A colorimetric determination of thorium

A colorimetric method for the determination of thorium is proposed. It is based upon the precipitation of thorium with a standard solution of oxalic acid and the subsequent reaction of the excess oxalic acid with a standard solution of potassium permanganate. The absorbancy of the remaining permanganate solution is directly proportional to the thorium present. The variables affecting this method have been critically studied. Reliable determinations can be made in the range of 3 to 30 mg of thorium in 1 cm cells when the colored solution is diluted to 250 ml. Most interfering substances can be removed by electrolysis in a mercury cathode cell or by the precipitation of thorium with potassium iodate.     

Gravimetric determination of silver as silver chromate

Summary Gravimetric estimation of silver, based upon its quantitative precipitation as normal silver chromate, Ag₂CrO₄, is described.     

Chromatographic separation and colorimetric determination of gold

Gold(III) is selectively sorbed from 1M hydrochloric acid by a short column containing a special acrylate resin. Then the gold is eluted from the column with acetone-hydrochloric acid, and the absorbance of the effluent is measured at 340 nm. Gold(III) may be successfully separated and determined in samples containing many other metal ions.     

Nanoscopic hybrid systems with a polarity-controlled gate-like scaffolding for the colorimetric signalling of long-chain carboxylates

Hybrid mesoporous systems containing a gate-like ensemble functionalised with imidazolium groups and a dye are used for the selective colorimetric sensing of long-chain carboxylates.     

Extraction of zinc with tri(iso-octyl)amine in methyl isobutyl ketone and colorimetric determination with zincon in the organic phase

A study was made of the extraction of zinc from hydrochloric acid solutions with solutions of methyldioctylamine and tri(iso-octyl)amine in methyl isobutyl ketone. Quantitative extraction was accomplished from 2 N hydrochloric acid with 5% (w/v) tri(iso-octyl)amine-methyl isobutyl ketone. A procedure was developed for the colorimetric determination of zinc in the organic phase after extraction using 2-carboxy-2'-hydroxy-5'-sulfoformazylbenzene (Zincon).     

Rapid colorimetric determination of indoxyl acetate

A rapid colorimetric method is presented for the determination of submilligram amounts of indoxyl acetate. The method depends upon the conversion of the indoxyl acetate into indigo.     

Extraction—spectrophotometric determination of traces of cadmium with 4-(2-pyridylazo)resorcinol and a long-chain quaternary ammonium salt

A simple and highly sensitive extraction—spectrophotometric determination of cadmium is described. The ion-associate formed between the cadmium-PAR anionic chelate and cetyldimethylbenzylammonium chloride (CDBA) is extracted with chloroform at pH 10. The absorption maximum of the extracted species occurs at 505 nm, the molar absorptivity being (9.82 ± 0.30) × 10⁴ l mol^-1 cm^-1. The optimal concentration range for measurements is 0.2–1.0 μg Cd ml^-1; Beer's law is obeyed. The composition of the ion-associate is estimated to be CdPAR₂-2CDBA. The conditional extraction constant is log K'_ex ≈ 8. The stability constant of the cadmium—PAR chelate in aqueous solution is log β₂ = 17.5 ± 0.3. Extraction with N-benzoyl-N-phenylhydroxylamine is used to avoid several interferences. Moderate amounts of zinc are masked with sodium hydroxide.     

A colorimetric method of determination of Borax

A method is described for the rapid and accurate determination of borax. The principle of this method is to cause the boron of the borax under analysis to form a complex by the addition of an excess of a fluoride , the excess of fluorine ions causes decolourization of the violet compound Fe(III) - sulphosalicylic acid by forming the colourless complex (FeF₆)^-3.The extinction coefficient of the solution, measured in the Pulfrich photometer, decreases with increasing content of this excess of fluorine ions, and consequently can be used as an indirect measure of the borax to be determined.     

Oxidants for the colorimetric determination of pindolol

A simple, sensitive and accurate colorimetric method is described for the quantitative determination of pindolol either in the pure form or in its tablets. The method is based on the oxidation of the indole moiety in pindolol with potassium persulphate or hydrogen peroxide-in acid medium-to give a highly coloured product that exhibits maximum absorption at 535 nm and 570 nm, respectively. Beer's law is obeyed over concentrations ranging from 0.07-0.35 mg/10 ml for potassium persulphate and 0.1-0.5 mg/10 ml for hydrogen peroxide with mean recoveries of 99.6+/-0.6 and 99.8+/-0.9%, respectively. The method is applied for the assay of pindolol tablets without any interference due to tablet fillers.     

Extraction—spectrophotometric determination of copper(II) with 4-(2-pyridylazo)resorcinol and a long-chain quaternary ammonium salt

A simple and highly sensitive extraction—spectrophotometric determination of copper (II) is described. The ion-associate formed between the copper(II)—4-(2-pyridylazo)-resorcinol (PAR) anion and tetradecyldimethylbenzylammonium chloride (TDBA) is extracted with chloroform at pH 9.7. The absorption maximum of the extracted species occurs at 510 nm, the molar absorptivity being 8.05 (± 0.07) × 10⁴ l mol^-1 cm^-1. Beer's Law is obeyed in the concentration range 0.1–0.5 μg Cu ml^-1. The composition of the ion-associate is estimated to be [Cu(PAR)₂(TDBA)₂]. The conditional extraction constant is log K'_ex ≈ 8. The interference of some cations and anions is studied. The method is suitable for analysis of waters.