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The characteristic color of a positive biuret test. In chemistry, the biuret test (IPA: / ˌ b aɪ j ə ˈ r ɛ t /, / ˈ b aɪ j ə ˌ r ɛ t / [1]), also known as Piotrowski's test, is a chemical test used for detecting the presence of at least two peptide bonds in a molecule.
Colorimetric assays use reagents that undergo a measurable color change in the presence of the analyte. They are widely used in biochemistry to test for the presence of enzymes, specific compounds, antibodies, hormones and many more analytes. For example, para-Nitrophenylphosphate is converted into a yellow product by alkaline phosphatase enzyme.
It gives a negative test-result for 25I-NBOMe and many other non-indole-related psychoactives. The reagent will also give a positive result for opium, because of the presence of tryptophan in natural opium. [3] Pyridoxine, present in vitamin supplements, can give positive results to the Ehrlich test, showing a pink colour change. [4]
The method combines the reactions of copper ions with the peptide bonds under alkaline conditions (the Biuret test) with the oxidation of aromatic protein residues. The Lowry method is based on the reaction of Cu +, produced by the oxidation of peptide bonds, with Folin–Ciocalteu reagent (a mixture of phosphotungstic acid and phosphomolybdic acid in the Folin–Ciocalteu reaction).
By using the Bradford protein assay, one can avoid all of these complications by simply mixing the protein samples with the Coomassie brilliant blue G-250 dye (Bradford reagent) and measuring their absorbances at 595 nm, which is in the visible range [8] and may be accurately measured by the use of a mobile smartphone camera. [9]
The Adamkiewicz reaction is part of a biochemical test used to detect the presence of the amino acid tryptophan in proteins. When concentrated sulfuric acid is combined with a solution of protein and glyoxylic acid, a red/purple colour is produced. It was named after its discoverer, Albert Wojciech Adamkiewicz.
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Pipetting anti-immunoglobulins to immunofixation panel. The panel simultaneously tests 4 patients (one in each quadrant). Each patient has 6 electrophoresis panels: The left one is a conventional serum protein electrophoresis. The remainder get solutions with anti-IgG, anti-IgA, anti-IgM, anti-kappa light chain and anti-lambda light chain ...