Classification | Colorimetric method |
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Analytes | Cholesterol, other sterols, indoles, terpenoids |
Salkowski's test, [1] also known simply as Salkowski test, is a qualitative chemical test, that is used in chemistry and biochemistry for detecting a presence of cholesterol and other sterols. [2] [3] [4] This biochemical method got its name after German biochemist Ernst Leopold Salkowski, [2] who is known for development of multiple new chemical tests, that are used for detection of different kinds of molecules (besides cholesterol and other sterols also for creatinine, carbon monoxide, glucose and indoles). [5] A solution that has tested positive on the Salkowski's test becomes red and gets yellow glow. [6]
For Salkowski test's procedure one needs a sample, that is to be tested for sterols, as well as chloroform and concentrated sulfuric acid that represent Salkowski's reagent. Usually the solution of chloroform and the sample is prepared first and later treated with concentrated sulfuric (VI) acid. After that the whole solution needs to be shaken well. [2] [6] It is important to use only dried glassware, as dehydration reaction occurs during the test's procedure. [7]
A solution that has tested positive on this qualitative chemical test exhibits two distinct layers in a test tube; the upper layer (chloroform) gets blueish red to violet colour, while the layer of sulfuric acid becomes yellow to green, with greenish glow being visible. If a sample does not contain any cholesterol or other sterols, colour of the tested solution remains unchanged and retains its original colour. [2] [8] [9]
Salkowski test can also be used to test the presence of indoles (crystalline alkaloids that are a degradation products of proteins, containg tryptophan [10] ). In such cases a sample is treated with nitric acid and 2% solution of potassium nitrite, with positive reaction being shown by presence of red colour. [11]
Treating a solution of a sample, containing sterols, with chloroform and highly hygroscopic sulfuric acid, leads to a dehydration reaction (two water molecules are removed from two cholesterol molecules) and formation of new double bonds. During the chemical reaction two sterols bind together and bisterol (bisteroid) is formed; bi-cholestadien (double cholestene with two double bonds) in a case of cholesterol. Red colour of a solution is a consequence of bi-sulfonic acid of a bi-cholestadien, which is a product of sulfuric acid sulfonating bi-cholestadien. [12] [13]
Marquis reagent is used as a simple spot-test to presumptively identify alkaloids as well as other compounds. It is composed of a mixture of formaldehyde and concentrated sulfuric acid, which is dripped onto the substance being tested. The United States Department of Justice method for producing the reagent is the addition of 100 mL of concentrated (95–98%) sulfuric acid to 5 mL of 40% formaldehyde. Different compounds produce different color reactions. Methanol may be added to slow down the reaction process to allow better observation of the colour change.
Chromic acid is jargon for a solution formed by the addition of sulfuric acid to aqueous solutions of dichromate. It consists at least in part of chromium trioxide.
Molisch's test is a sensitive chemical test, named after Austrian botanist Hans Molisch, for the presence of carbohydrates, based on the dehydration of the carbohydrate by sulfuric acid or hydrochloric acid to produce an aldehyde, which condenses with two molecules of a phenol, resulting in a violet ring.
In chemistry, a chemical test is a qualitative or quantitative procedure designed to identify, quantify, or characterise a chemical compound or chemical group.
2,4-Dinitrophenylhydrazine (2,4-DNPH or DNPH) is the organic compound C6H3(NO2)2NHNH2. DNPH is a red to orange solid. It is a substituted hydrazine. The solid is relatively sensitive to shock and friction. For this reason DNPH is usually handled as a wet powder. DNPH is a precursor to the drug Sivifene.
Phosphorus pentoxide is a chemical compound with molecular formula P4O10 (with its common name derived from its empirical formula, P2O5). This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant and dehydrating agent.
Isoamyl alcohol is a colorless liquid with the formula C
5H
12O, specifically (H3C–)2CH–CH2–CH2–OH. It is one of several isomers of amyl alcohol (pentanol). It is also known as isopentyl alcohol, isopentanol, or (in the IUPAC recommended nomenclature) 3-methyl-butan-1-ol. An obsolete name for it was isobutyl carbinol.
In chemistry, the Biuret test, also known as Piotrowski's test, is a chemical test used for detecting the presence of at least two peptide bonds in a molecule. In the presence of peptides, a copper(II) ion forms mauve-colored coordination complexes in an alkaline solution. The reaction was first observed in 1833; In Poland, the biuret test is also known as Piotrowski's test in honor of the Polish physiologist Gustaw Piotrowski who independently rediscovered it in 1857. Several variants on the test have been developed, such as the BCA test and the Modified Lowry test.
Acid guanidinium thiocyanate-phenol-chloroform extraction is a liquid–liquid extraction technique in biochemistry. It is widely used in molecular biology for isolating RNA. This method may take longer than a column-based system such as the silica-based purification, but has higher purity and the advantage of high recovery of RNA: an RNA column is typically unsuitable for purification of short RNA species, such as siRNA, miRNA, gRNA and tRNA.
The Liebermann–Burchard or acetic anhydride test is used for the detection of cholesterol. The formation of a green or green-blue colour after a few minutes is positive.
Reagent testing is one of the processes used to identify substances contained within a pill, usually illicit substances. With the increased prevalence of drugs being available in their pure forms, the terms "drug checking" or "pill testing" may also be used, although these terms usually refer to testing with a wider variety of techniques covered by drug checking.
para-Dimethylaminobenzaldehyde is an organic compound containing amine and aldehyde moieties which is used in Ehrlich's reagent and Kovac's reagent to test for indoles. The carbonyl group typically reacts with the electron rich 2-position of the indole but may also react at the C-3 or N-1 positions. It may also be used for determination of hydrazine.
The IMViC tests are a group of individual tests used in microbiology lab testing to identify an organism in the coliform group. A coliform is a gram negative, aerobic, or facultative anaerobic rod, which produces gas from lactose within 48 hours. The presence of some coliforms indicate fecal contamination.
Ernst Leopold Salkowski was a German biochemist who was a native of Königsberg.
Desmosterol (Cholesta-5,24-dien-3β-ol) is a lipid present in the membrane of phytoplankton and an intermediate product in cholesterol synthesis in mammal cells. Structurally, desmosterol has a similar backbone to cholesterol, with the exception of an additional double bond in the structure of desmosterol.
Ehrlich's reagent or Ehrlich reagent is a reagent containing p-dimethylaminobenzaldehyde (DMAB) and thus can act as an indicator to presumptively identify indoles and urobilinogen. Several Ehrlich tests use the reagent in a medical test; some are drug tests and others contribute to diagnosis of various diseases or adverse drug reactions. It is named after Nobel Prize winner Paul Ehrlich who used it to distinguish typhoid from simple diarrhoea.
Indole is an aromatic, heterocyclic, organic compound with the formula C8H7N. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indole is widely distributed in the natural environment and can be produced by a variety of bacteria. As an intercellular signal molecule, indole regulates various aspects of bacterial physiology, including spore formation, plasmid stability, resistance to drugs, biofilm formation, and virulence. The amino acid tryptophan is an indole derivative and the precursor of the neurotransmitter serotonin.
p-Dimethylaminocinnamaldehyde (DMACA) is an aromatic hydrocarbon. It is used in an acidic solution to detect indoles.
The Hopkins-Cole reaction, also known as the glyoxylic acid reaction, is a chemical test used for detecting the presence of tryptophan in proteins. A protein solution is mixed with Hopkins Cole reagent, which consists of glyoxylic acid. Concentrated sulfuric acid is slowly added to form two layers. A purple ring appears between the two layers if the test is positive for tryptophan. Nitrites, chlorates, nitrates and excess chlorides prevent the reaction from occurring.
A spot test in lichenology is a spot analysis used to help identify lichens. It is performed by placing a drop of a chemical on different parts of the lichen and noting the colour change associated with application of the chemical. The tests are routinely encountered in dichotomous keys for lichen species, and they take advantage of the wide array of lichen products produced by lichens and their uniqueness among taxa. As such, spot tests reveal the presence or absence of chemicals in various parts of a lichen. They were first proposed by the Finnish lichenologist William Nylander in 1866.
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(help)Salkowski test for cholesterol – Its principle and procedure