New spot test for urea based on colorimetric reaction with chloranil

A new spot test for urea is described. It is based on reaction with chloranil, in aqueous solutions, to give a violet color due to the formation of 2,5-dichloro-3-amino-6-hydroxy-p-benzoquinone. The lower limit of identification is 10 μg. Amines, amides, imides, thiourea, urea nitrate, and diphenyl urea do not interfere with the test.     

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.     

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.     

Spectrophotometric flow-injection determination of zinc in plant digests based on a spot test

A spot test was implemented in a flow-injection system for the spectrophotometric determination of zinc in digests of plant materials. It is based on the influence of Zn²⁺ on the oxidation rate of 1-naphthylethylenediamine (NED) by hexacyanoferrate(III) under acidic conditions. In order to control the precipitate formation and to maintain the resulting suspension, a micellar medium was established by adding Triton X-100. The proposed system handles about 65 samples per hour, meaning 72 μg NED and 9.0 mg K₃[Fe(CN)₆] per determination. Baseline drift is usually <0.01 absorbance per hour and the analytical signals for 0.5-2.5 mg l⁻¹ Zn range within ca. 0.07-0.45 absorbance. Linearity of the analytical curve is fair (r>0.999, n=6) and detection limit was estimated as 0.2 mg l⁻¹ Zn. Results are precise (R.S.D.<1%, n=10) and in agreement with flame atomic absorption spectrometry and with certified values of standard reference materials.     

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.     

A spot test for ferricyanide

Summary 0.02 g/0.2 ml of potassium ferricyanide can be detected on a spot plate by utilising its catalytic effect on the reaction of cerium (III) with sulphosalicylic acid. A probable mechanism is discussed.

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Zusammenfassung Die katalytische Wirkung von Hexacyanoferrat(III) auf die Reaktion zwischen Cer(III) und Sulfosalicylsäure wird zur einem empfindlichen Tüpfelnachweis für [Fe(CN)₆]^3– benutzt. Noch 0,02 g/0,2 ml können nachgewiesen werden. Der Reaktionsmechanismus wird diskutiert.

     

Selective spot test for hydrazine

Trinitrobenzene sulphonic acid reacts with hydrazine in dilute aqueous solution to give a violet colour. This reaction is used as the basis of a sensitive spot test for hydrazine.     

A spot test for nitrates

Summary At a dilution of 1:200.000, and in the presence of excess sulfuric acid, as little as 0.2 g nitrate ion forms a yellow color with chroniotropic acid. Interfering colors due to nitrites and oxidizing agents are eliminated by previous treatment of the test sample with sodium sulfite, sulfuric acid, and sulfamic acid.

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Zusammenfassung Bis zu einer Verdünnung von 1 200000 geben noch 0,2 g Nitration bei Gegenwart überschüssiger Schwefelsäure mit Chromotropsäure eine gelbe Farbe. Störende Farbreaktionen durch Nitrit und andere Oxydationsmittel lassen sich durch vorhergehende Behandlung der Probe mit Natriumsulfit, Schwefelsäure und Amidosulfonsäure ausschalten.

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Résumé En quantités de l'ordre de grandeur de 0,2g, à une dilution de 1 200000 et en présence d'un excès d'acide sulfurique, les ions nitrate donnent une coloration jaune avec l'acide chromotropique. Les colorations gênantes dûes aux nitrites et aux réactifs oxydants sont éliminées par un traitement préalable de l'échantillon à examiner à l'aide de sulfite de sodium et des acides sulfurique et sulfamique.

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Dedicated to Prof.Hans Lieb on occasion of his 70th birthday.     

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.     

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.     

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.     

A new colorimetric test for solid-phase amines and thiols

A new, efficient, sensitive, and reliable color test for the visual detection of resin-bound primary and secondary amines is described. The reaction between amines and 1-methyl-2-(4'-nitrophenyl)-imidazo[1,2- a]pyrimidinium perchlorate (DESC) provides the "on-bead generated" colored stable intermediate azadiene. The developed protocols allow detection of resin-bound primary amines in the presence of secondary amines. The test can also be used for the detection of resin bound thiols.     

A new spot test for palladium

A new Spot test foi palladium is based upon the formation of an orange-yellow chelate with phenyl-α-pyridyl ketoxime Interference by the metals usually associated with palladium can be easily and completely prevented. Lumit of identification 0 5μg Pd