Colour reaction test

Due to the (often) highly coloured nature of fungi, it is advisable to pre-extract the drugs which might be present, in order that colour reaction tests are not... 

The Burchfield colour reaction test is used to confirm the specific identity of a range of elastomers. The test results in colour changes before and after heating the test mixture (Braun, 1986). 

Colour Reactions. Rochelmeyer (1939) has provided a list of colour reactions given by solasodine and solasodiene (solanosodine), with reagents usually applied to the sterols, and Briggs et al. have found that when concentrated sulphuric acid (1 mil) is carefully added to a solution of solasonine or solasodine in hot alcohol (1 mil) a characteristic, intense, greenish-yellow fluorescence is produced, a reaction which is not given by solanine or solanidine. They have also found that intense colours are formed when solasonine or solasodine is mixed with resorcinol, or one of a variety of aldehydes, and boiled with concentrated hydrochloric acid. Colours are also produced with this test by cholesterol, digitonin, jacobine carbazole, pyrrole, or nicotine, the most intense colours being formed with p-hydroxybenzaldehyde or anisaldehyde. 

Comparisons of the ultra-violet absorption spectra of the four hydrocarbons have been made with those of a series of condensed ring hydrocarbons and it is tentatively concluded that they may be derivatives of either epeiopentenophenanthrene or epeZopentenofluorene. All four hydrocarbons give a colour reaction in the Vanseheidt test. ... 

A solution of iodine in aqueous iodide has an intense yellow to brown colour. One drop of 0.05M iodine solution imparts a perceptible pale yellow colour to 100 mL of water, so that in otherwise colourless solutions iodine can serve as its own indicator. The test is made much more sensitive by the use of a solution of starch as indicator. Starch reacts with iodine in the presence of iodide to form an intensely blue-coloured complex, which is visible at very low concentrations of iodine. The sensitivity of the colour reaction is such that a blue colour is visible when the iodine concentration is 2 x 10 " 5 M and the iodide concentration is greater than 4x 10 4M at 20 °C. The colour sensitivity decreases with increasing temperature of the solution thus at 50 °C it is about ten times less sensitive than at 25 °C. The sensitivity decreases upon the addition of solvents, such as ethanol no colour is obtained in solutions containing 50 per cent ethanol or more. It cannot be used in a strongly acid medium because hydrolysis of the starch occurs. 

Dry the ethereal solution with a small piece of potassium hydroxide and evaporate the ether, when the diamine formed algng with the sulphanilic acid remains it can be recognised by the colour reaction described on p. 319 (Wurster s red). It becomes crystalline on cooling. Its acetyl derivative, which is obtained by warming the crude base on the water bath for a short time with 0-5 c.c. of acetic anhydride (in a test tube,) is also suitable for characterising the diamine. The solution is diluted with water and, since the acetyl... 

The limit test for phosphate is based upon the formation of ayellow colour reaction with molybdovanadic reagent (combination of ammonium vanadate and ammonium molybdate) in an acidic medium. However, the exact composition of the molybdovanadophosphoric acid complex is yet to be established. 

Starch consists of two main components amylose (insoluble in cold water) and amylopectin (soluble in cold water). Amylose, which accounts for about 20 per cent by weight of starch, has an average molecular weight of over 10. It is a polymer of glucopyranose units linked together through a l,4 -linkages in a linear chain. Hydrolysis of amylose produces maltose. Amylose and iodine form a colour complex, which is blue/black. This is the colour reaction of iodine in starch, a confirmatory test for the presence of starch. 

Preparation of Copper(II) Bromide. Introduce 1-2 g of a copper powder into a beaker with 50 ml of water and while stirring the reaction mixture, slowly add 3-6 drops of bromine from a dropping funnel. When the reaction terminates, cool the solution, filter it through ordinary cotton wool inserted into a glass funnel, boil it with charcoal (for what purpose ), and evaporate it in a vacuum desiccator. Filter off the formed crystals on a funnel with a filtering bottom. What is the composition of the product Write the equation of the reaction. Test how the copper bromide crystals behave in water and when heated. To do this, put 5-6 small crystals of the salt into each of two test tubes. Carefully add water dropwise to one of the tubes until the solution acquires a light blue colour, and then introduce about 0.2 g of dry potassium bromide, and heat the second tube. What happens Explain the observed phenomena. 

Against a white surface this colour reaction may be observed even with a 0-00001 per cent, concentration of selenious acid. The reaction is more sensitive with sulphuric acid above 75 per cent, concentration than with dilute acid. The test is not applicable if the sulphuric acid contains iron. Tellurous acid retards the reaction.1... 

If the test for the enzymes gives positive results—the liquid in the tubes being coloured yellowish brown, red or reddish brown—and the colour reactions are given, the product most probably consists of a mixture of natural honey with commercial invert sugar. 

Behaviour towards other Pigments.—Some mineral colours may be mixed to obtain intermediate tints, whereas others cannot be so mixed as reactions would occur altering profoundly their properties and colour. To test if two colours are miscible, they are intimately mixed in a mortar and (if no immediate change occurs) the mixture kept, partly in the light, partly in the dark, and examined from time to time. Change sometimes take place immediately or after a short time, and sometimes only after some years if the mixture is heated with a little water, the reactions occur rapidly. 

Some of the tests involved relatively simple colour reactions such as the Baudouin reaction for sesame oil, and the Halphen test for cottonseed oil. In both cases a compound characteristic to an oil is used to determine the presence of the oil. Here again the test detected a component that today would be detected and quantified by gas chromatography (GC) or high performance liquid chromatography (HPLC). It was even possible to determine the presence of cholesterol or phytosterols, although, after separation, the identification as to which type was present depended on microscopic examination and fractional... 

Pharmacopoeial applications include assays for single drugs and mixtures of drugs, analyses involving colour reactions (colorimetric methods), tests for tablet dissolution, limit tests for impurities, and assays of bulk drugs or an extract thereof. Further applications are for physicochemical measurements, such as pK or velocity constants in enzymatic reactions. The scope of such applications has been significantly extended by methods which can confer additional specificity, namely difference spectrophotometry and derivative spectrophotometry. 

Following the possible identification of the presence of LSD, the next stage in the analysis is the use of thin layer chromatography (TLC). This is employed because although it cannot be used to prove the identity of LSD, it can be used as a rapid, cost-effective method to eliminate those samples which gave a positive colour reaction in the presumptive tests but which do not contain this drug. These will be rarer when blotter acids are suspected, but may be more common where other substrates have been used as the carrier medium for the LSD itself. 

Table 5.1 Colour reactions observed on reacting opiates with common presumptive test reagents (see Appendix 1)...

A number of difficulties are associated with colour tests on fresh and dried plant material, in addition to those associated with analysing a primary amine such as mescaline. These include the fact that the plant material itself may obscure the colour reaction that takes place. Furthermore, a wide range of primary phenethy-lamines and amphetamines may yield similar colour reactions. The presumptive test which can be satisfactorily used is the Marquis test (see Appendix 1). Positive and negative control tests should also be carried out. An orange-red colour will develop if mescaline is present. However, due to the difficulties associated with interpretation of such results, further confirmation of the presence of mescaline, by using chromatographic and spectroscopic techniques, is required. 

This reagent is prepared as a 1% solution of ammonium metavanadate in concentrated sulfuric acid, which is then added directly to the test substrate. Orange colour reactions are observed with cocaine and related compounds, with olive green colours being produced if opiates are present. 

This is prepared by dissolving 5 ml of 40% formaldehyde in 100 ml of concentrated sulfuric acid. The reagent is then added directly to the test substrate. A purple-olive coloration is produced with opiates, and yellow-orange with amphetamine, methylamphetamine, psilocybin and psilocin, among others. A grey-purple colour reaction is obtained with ring-substituted amphetamines. 

Other Colour Reactions. On boiling the substance to be tested with an alcoholic solution of potassium hydroxide and then adding a few ml. of thymol, a yellow colouration appears in the presence of chloropicrin and this changes to reddish-violet on addition of sulphuric acid. 

Colour Reactions of Proteins - The colour reactions of proteins are of importance in the qualitative detection and quantitative estimation of proteins and their constituent amino acids. Biuret test is extensively used as a test to detect proteins in biological materials. 

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