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Fading colourant

The fluorescent alkaloid zones in the R, range 0.15-0.85 respond to DRG reagent with brown, rapidly fading colours (vis.). Papaverine (T2) can serve as reference conipoimd for sanguinarine (Rf 0.4), and methyl red (T3) for the alkaloidal zones at R, -- 0.8. [Pg.41]

The reduction of oxidized quercetin by cephem analogs was used in development of visible spectrophotmetric method for determination of P-lactam analogs. Quercetin is a flavonol (3,5,7,3, 4 - pentahydroxyflavone) which is oxidized by N-bromosuccinimide giving reddish green colour (Xmax = 510 nm). As the result of reduction of oxidized form of quercetin by cephem analog fade colour was observed (Fig. 9). This colour is the result of formation of o-quinone derivative of quercetin under the mild oxidants [34],... [Pg.118]

The position of the spots should be marked in pencil, for the colours fade after some time. [Pg.53]

Dissolve a few drops of nitromethane in 10% sodium hydroxide solution. Add a few crystals of sodium nitrite and shake. Now add dilute sulphuric acid drop by drop. A brownish-red coloration develops, but fades again when an excess of acid is added. The sulphuric acid has thus liberated nitrous acid, which has in turn reacted with the nitromethane to give a nitrolic acid, the sodium salt of which is CH3NO2 + ONOH = CH(N02) N0H + HgO reddish-brown in colour, probably owing to mesomeric ions of the type ... [Pg.134]

Now add more dilute sulphuric acid drop by drop the colour almost completely fades, as salt formation occurs on both nitrogen atoms with suppression of the resonance hybrid formation. [Pg.303]

Hydrolysis of methyl oxalate. The exceptionally rapid hydrolysis of rnethyl oxalate can be followed thus Dissolve 0 2 g. of finely powdered methyl oxalate in 10 ml. of water, and add i drop of phenolphthalein. Then add very dil. NaOH solution (1%) drop by drop until the solution just turns pink it will be noticed that the colour rapidly fades, but is restored on the Further addition of 1-2 drops of NaOH solution. The colour fades again and the addition can be repeated until hydrolysis is complete. Oxalic acid (with which methyl oxalate may be confused) gives a precise end-point when treated with NaOH solution in this way. [Pg.357]

The following simple test distinguishes fructose from all other carbohydrates. Upon heating a little fructose with dilute cobalt chloride solution, cooling and treating with a little ammonia solution, a violet to purple colour is developed, - the colour gradually fades and must be observed immediately after the addition of the ammonia solution. Green cobalt hydroxide is formed with all other carbohydrates. [Pg.456]

The solid is pale blue the liquid is an intense blue at low temperatures but the colour fades and becomes greenish due to the presence of NO2 at higher temperatures. The dissociation also limits the precision with which physical properties of the compound can be determined. At 25°C the dissociative equilibrium in the gas phase is characterized by the following thermodynamic quantities ... [Pg.454]

Pipette 25 mL of the bismuth solution (approx. 0.01 M) into a 500 mL conical flask and dilute with de-ionised water to about 150 mL. If necessary, adjust the pH to about 1 by the cautious addition of dilute aqueous ammonia or of dilute nitric acid use a pH meter. Add 30 mg of the xylenol orange/potassium nitrate mixture (see Section 10.50) and then titrate with standard 0.01 M EDTA solution until the red colour starts to fade. From this point add the titrant slowly until the end point is reached and the indicator changes to yellow. [Pg.324]

The great merit of starch is that it is inexpensive. It possesses the following disadvantages (1) insolubility in cold water (2) instability of suspensions in water (3) it gives a water-insoluble complex with iodine, the formation of which precludes the addition of the indicator early in the titration (for this reason, in titrations of iodine, the starch solution should not be added until just prior to the end point when the colour begins to fade) and (4) there is sometimes a drift end point, which is marked when the solutions are dilute. [Pg.387]

Only freshly prepared starch solution should be used. Two millilitres of a 1 per cent solution per 100 mL of the solution to be titrated is a satisfactory amount the same volume of starch solution should always be added in a titration. In the titration of iodine, starch must not be added until just before the end point is reached. Apart from the fact that the fading of the iodine colour is a good indication of the approach at the end point, if the starch solution is added when the iodine concentration is high, some iodine may remain adsorbed even at the end point. The indicator blank is negligibly small in iodimetric and iodometric titrations of 0.05M solutions with more dilute solutions, it must be determined in a liquid having the same composition as the solution titrated has at the end point. [Pg.388]

After the addition of the potassium iodide solution, run in standard 0.1M sodium thiosulphate until the brown colour of the iodine fades, then add 2 mL of starch solution, and continue the addition of the thiosulphate solution until the blue colour commences to fade. Then add about 1 g of potassium thiocyanate or ammonium thiocyanate, preferably as a 10 per cent aqueous solution the blue colour will instantly become more intense. Complete the titration as quickly as possible. The precipitate possesses a pale pink colour, and a distinct permanent end point is readily obtained. [Pg.394]

Procedure. Weigh out accurately about 10 g of the salt and dissolve it in 250 mL of water in a graduated flask. Pipette 25 mL of this solution into a 250 mL conical flask, add about 20 mL of 10 per cent potassium iodide solution, 2 mL of 1M sulphuric acid, and 15 mL of a solution containing 2.0 g crystallised zinc sulphate. Titrate the liberated iodine immediately with standard 0.1M sodium thiosulphate and starch add the starch solution (2 mL) after the colour has faded to a pale yellow. The titration is complete when the blue colour has just... [Pg.399]

The titrations should be carried out slowly so that the indicator change, which is a time reaction, may be readily detected. If the determinations are to be executed rapidly, the volume of the bromate solution to be used must be known approximately, since ordinarily with irreversible dyestuff indicators there is no simple way of ascertaining when the end point is close at hand. With the highly coloured indicators (xylidine ponceau, fuchsine, or naphthalene black 12B), the colour fades as the end point is approached (owing to local excess of bromate) and another drop of indicator can be added. At the end point the indicator is irreversibly destroyed and the solution becomes colourless or almost so. If the fading of the indicator is confused with the equivalence point, another drop of the indicator may be added. If the indicator has faded, the additional drop will colour the solution if the end point has been reached, the additional drop of indicator will be destroyed by the slight excess of bromate present in the solution. [Pg.405]

To determine the purity of a sample of arsenic(III) oxide follow the general procedure outlined in Section 10.127 but when the 25 mL sample of solution is being prepared for titration, add 25 mL water, 15 mL of concentrated hydrochloric acid and then two drops of indicator solution (xylidine ponceau or naphthalene black 12B see Section 10.125). Titrate slowly with the standard 0.02M potassium bromate with constant swirling of the solution. As the end point approaches, add the bromate solution dropwise with intervals of 2-3 seconds between the drops until the solution is colourless or very pale yellow. If the colour of the indicator fades, add another drop of indicator solution. (The immediate discharge of the colour indicates that the equivalence point has been passed and the titration is of little value.)... [Pg.407]

Molybdenum(VI), vanadium(V), mercury, and iron interfere permanganates, if present, may be removed by boiling with a little ethanol. If the ratio of vanadium to chromium does not exceed 10 1, nearly correct results may be obtained by allowing the solution to stand for 10-15 minutes after the addition of the reagent, since the vanadium-diphenylcarbazide colour fades fairly rapidly. Vanadate can be separated from chromate by adding oxine to the solution and extracting at a pH of about 4 with chloroform chromate remains in the aqueous solution. Vanadium as well as iron can be precipitated in acid solution with cupferron and thus separated from chromium (III). [Pg.687]

Procedure. Dissolve the sample in distilled water and take an aliquot which should contain not more than 50 pg of phenolic compound. Use the aqueous ammonia to adjust the pH of the solution to 9.7-10.3 (pH meter), and then dilute to 500 mL with distilled water. Transfer the solution to a large separatory funnel, add 1.0 mL of solution A followed by 10 mL of solution B. Shake well to ensure thorough mixing, and then carry out three extractions with successive portions of 15 mL, 10 mL and 5 mL of chloroform (trichloromethane). Combine the chloroform extracts and make up the volume to 30 mL. Measure the absorbance of the extract against a blank of chloroform at a wavelength of 460 nm (blue filter), using 1 cm cells. The colour may tend to fade after 10 minutes and so speed is essential. [Pg.708]

Method of Preparation Dissolve 1 g of phenol and 4 mL of liquid Br2 separately in 10-15 mL of glacial acetic acid. Add Br2 solution to phenol solution until the decolourisation of bromine ceases. Allow the mixture to stand for 20 min and add more bromine solution, if the colour faded. Pour the liquor into 70 mL of water and filter the product. Wash with water and recrystallise in ethanol. [Pg.386]

M.P. Colombini, A. Andreotti, C. Baraldi, I. Degano, J.J. tucejko, Colour fading in textiles A model study on the decomposition of natural dyes, Microchemical Journal, 85, 174 182 (2007). [Pg.35]

The other stability problem with curcumin is sulfur dioxide. If the sulfur dioxide level is above 100 ppm then the colour will fade. [Pg.95]

After a while, sodium ions from the salt swap for the iron ion at the centre of the haem ring. There is no longer a couple (one component is lost), and consequently no scope for an MLCT transition, so the red colour of the blood fades. [Pg.462]


See other pages where Fading colourant is mentioned: [Pg.116]    [Pg.261]    [Pg.49]    [Pg.1]    [Pg.116]    [Pg.261]    [Pg.49]    [Pg.1]    [Pg.186]    [Pg.275]    [Pg.449]    [Pg.241]    [Pg.941]    [Pg.599]    [Pg.143]    [Pg.688]    [Pg.373]    [Pg.401]    [Pg.12]    [Pg.165]    [Pg.157]    [Pg.241]    [Pg.456]    [Pg.144]    [Pg.718]    [Pg.75]    [Pg.5]    [Pg.98]    [Pg.347]    [Pg.282]    [Pg.284]    [Pg.161]    [Pg.339]   
See also in sourсe #XX -- [ Pg.304 ]




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