Chromatography dichromate

The consumption of the oxime can be checked by thin-layer chromatography on silica gel G with the solvent system chloro-form/methanol (95/5 v/v) and a spray reagent consisting of 5% potassium dichromate in 40% sulfuric acid. The oxime appears as an immediate dark spot and the aziridine as a yellow spot. The checkers observed identical mobilities (Rf 0.8) for both compounds. 

Elemental composition K 28.22%, Cl 25.59%, and 0 46.19%. An aqueous solution is analyzed for potassium by AA, ICP, and other methods (see Potassium). Perchlorate ion may be analyzed by ion chromatography or a liquid-membrane electrode. Iodide, bromide, chlorate, and cyanide ions interfere in the electrode measurement. Alternatively, perchlorate ion may be measured by redox titration. Its solution in 0.5M H2SO4 is treated with a measured excess standard ferrous ammonium sulfate. The excess iron(II) solution is immediately titrated with a standard solution of potassium dichromate. Diphenylamine sulfuric acid may be used as an indicator to detect the end point ... 

In the following experiments cyclohexanol is oxidized to cyclohexanone using pyridinium chlorochromate in dichloromethane. The progress of the reaction can be followed by thin-layer chromatography. On a larger scale this reaction would be carried out using sodium dichromate in acetic acid because the reagents are less expensive, the reaction is faster, and much less solvent is required. 

The method using the picrate [Packer et al. J Am Chem Soc 80 905 1958] is as follows quinoline is added to picric acid dissolved in the minimum volume of 95% EtOH, giving yellow crystals which were washed with EtOH, air-dried and crystaUised from acetonitrile. These were dissolved in dimethyl sulfoxide (previously dried over 4A molecular sieves) and passed through a basic alumina column, onto which the picric acid is adsorbed. The free base in the effluent is extracted with w-pentane and distilled under vacuum. Traces of solvent can be removed by vapour-phase chromatography. [Moonaw Anton / PAyj Chem 80 2243 1976.] The ZnCl2 and dichromate complexes have also been used [Cumper et al. J Chem Soc 1176 1962]. [Beilstein 20 H 339,20 I 134, 20 II 222, 20 III/IV 3334, 20/7 V 276.]... 

Once a sample is in solution, the solution conditions must be adjusted for the next stage of the analysis (separation or measurement step). For example, the pH may have to be adjusted, or a reagent added to react with and mask interference from other constituents. The analyte may have to be reacted with a reagent to convert it to a form suitable for measurement or separation. For example, a colored product may be formed that wUl be measured by spectrometry. Or the analyte will be converted to a form that can be volatilized for measurement by gas chromatography. The gravimetric analysis of iron as FeaOa requires that all the iron be present as iron(in), its usual form. A volumetric determination by reaction with dichromate ion, on the other hand, requires that all the iron be converted to iron(II) before reaction, and the reduction step will have to be included in the sample preparatioii. 

Many chemicals are available that can be used without further purification. Their selection is made on a trial and error basis, and even different lots from the same supplier may differ in purity. Volatile buffers and solvents such as pyridine, acetic acid, formic acid, and n-propanol, which are employed for chromatography, can be purified by distillation over ninhydrin. Constant-boiling hydrochloric acid is rountinely prepared over sodium dichromate (Schwabe and Catlin, 1974), and water of high purity is obtained from a system composed of a 0.2-fim particle filter, an activated charcoal cartridge, and two deionizer cartridges (Hydro Service and Supplies, Durham, North Carolina). The solvents are tested for purity in the following manner. A sample of the solvent is dried in vacuo. The residue is dissolved in pH 2.2 citrate buffer and injected onto the amino acid analyzer column. The distilled solvents are typically found to contain aspartic acid, serine, and glycine at 20-30 pmol/ml as the major contaminants. 

Radhakrishnan and Rao [1] have studied the kinetics and mechanism of the degradation of thiol terminated polysulfide polymers HS(RSS) RSH, R-CH -CH OCH -OCH -CH - which have been cured with ammonium dichromate using pyrolysis-gas chromatography (Py-GC) and isothermal and dynamic thermogravimetric analysis (TGA). 

Some individual substances may however be chemically modified during this test. Nichaman et al. [475] have reported the iodination of polyunsaturated fatty acids and the results of the subsequent gas-liquid chromatography which were thereby rendered inaccurate. Localisation with iodine, extraction and quantitative determination with dichromate solution has been described for lipids [19] the interfering 10 ... 

A solution of potassium dichromate in sulphuric acid has been used for the detection of classes of amines according to the colour changes observed , and in thin-layer chromatography for the identification of arylamines . Ceric sulphate in sulphuric acid can be used for spotting alkaloids and probably other bases in thin-layer chromatography . A standard solution of ceric sulphate was used for determining p-methylaminophenol . 

Radhakrishnan, T. S., and Rama Rao, M., Kinetics and Mechanism of the Thermal Degradation of Polysulfide Polymer Cured with Ammonium Dichromate/Pyrolysis-Gas Chromatography and Thermogravimetric Stxi6aes,J. Anal. Appl. Pyrolysis, 9 309-322 (1986)... 

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