Colour tests methods Sommaire 1 Amalic acid test (test for xanthines) 1.1 Method 1.2 Indications 2 Ammoniacal silver nitrate 2.1 Reagent 2.2 Method 2.3 Indications 3 Antimony pentachloride 3.1 Reagent 3.2 Method 3.3 Indications 4 Aromaticity 4.1 Method 1 4.1.1 Indications 4.2 Method 2 4.2.1 Indications 5 Benedict’s reagent 5.1 Reagent 5.2 Method 5.3 Indications 6 Carbon disulfide 6.1 Method 6.2 Indications 7 Chromotropic acid 7.1 Reagent 7.2 Method 8 Cobalt thiocyanate (see Scott’s test) Analytical Toxicology - Colour tests methods | 1 Colour tests methods 8.1 Reagent 8.2 Method 9 Coniferyl alcohol (primary aromatic amines) 9.1 Reagent 9.2 Method 9.3 Indications 10 Copper sulfate 10.1 Method 1 10.2 Indications 10.3 Method 2 10.4 Indications 11 Cyanogen bromide 11.1 Reagent 11.2 Method 11.3 Indications 12 Diazotisation 12.1 Method 12.2 Indications 13 Dille–Koppanyi reagent modified (a general test for barbiturate–like compounds) 13.1 Reagent 13.2 Method 13.3 Indications 14 p-Dimethylaminobenzaldehyde (Wasicky reagent or Van Urk reagent; a general test for ergot alkaloids) 14.1 Reagent 14.2 Method 14.3 Indications 15 Diphenylamine test 15.1 Reagent Analytical Toxicology - Colour tests methods | 2 Colour tests methods 15.2 Method 15.3 Indications 16 Dragendorff reagent (a general reagent for nitrogenous bases) 16.1 Reagent 16.2 Method 16.3 Indications 17 Duquenois reagent, modified 17.1 Reagent 17.2 Method 17.3 Indications 18 Ferric chloride (general reagent for phenols, e.g. salicylates) 18.1 Reagent 18.2 Method 18.3 Indications 19 Ferrous sulfate A (test for nitrates and nitrites) 19.1 Reagent 19.2 Method 19.3 Indications 20 Ferrous sulfate B (test for cyanide) 20.1 Reagent 20.2 Method 20.3 Indications 21 Folin–Ciocalteu reagent (test for phenolic compounds) 21.1 Reagent 21.2 Method 21.3 Indications 22 Formaldehyde–sulfuric acid 22.1 Reagent 22.2 Method Analytical Toxicology - Colour tests methods | 3 Colour tests methods 22.3 Indications 23 Forrest reagent 23.1 Reagent 23.2 Method 23.3 Indications 24 FPN reagent (general reagent for phenothiazines) 24.1 Reagent 24.2 Method 24.3 Indications 25 Froehde reagent 25.1 Reagent 25.2 Method 26 Fujiwara test (general reagent for halogenated hydrocarbons) 26.1 Reagent 26.2 Method 26.3 Indications 27 Furfuraldehyde (general reagent for carbamates) 27.1 Reagent 27.2 Method 27.3 Indications 28 Iodine test 28.1 Method 28.2 Indications 29 Iodoplatinate test (general test for alkaloids and nitrogenous heterocyclic compounds) 29.1 Reagent 29.2 Method 29.3 Indications 30 Koppanyi–Zwikker test Analytical Toxicology - Colour tests methods | 4 Colour tests methods 30.1 Reagent 30.2 Method 30.3 Indications 31 Liebermann’s reagent 31.1 Reagent 31.2 Method 31.3 Indications 32 Mandelin’s test (useful test for amfetamines and antidepressants) 32.1 Reagent 32.2 Method 32.3 Indications 33 Marquis test 33.1 Reagent 33.2 Method 33.3 Indications 34 McNally’s test 34.1 Reagents 34.2 Method 34.3 Indications 35 Mecke’s reagent (useful test for opium alkaloids) 35.1 Reagent 35.2 Method 35.3 Indications 36 Melzer’s reagent (general reagent for hallucinogenic mushrooms) 36.1 Reagent 36.2 Method 36.3 Indications 37 Mercurous nitrate (general reagent for barbiturate–like compounds) 37.1 Reagent Analytical Toxicology - Colour tests methods | 5 Colour tests methods 37.2 Method 37.3 Indications 38 Methanolic potassium hydroxide 38.1 Reagent 38.2 Method 38.3 Indications 39 Millon’s reagent (general reagent for phenols) 39.1 Reagent 39.2 Method 39.3 Indications 40 Naphthol–sulfuric acid 40.1 Reagent 40.2 Method 40.3 Indications 41 Nessler’s reagent 41.1 Reagent 41.2 Method 41.3 Indications 42 Ninhydrin 42.1 Reagent 42.2 Method 42.3 Indications 43 Nitric acid, fuming 43.1 Method 43.2 Indications 44 Nitric–sulfuric acid (Erdmann’s reagent) 44.1 Reagent 44.2 Method 44.3 Indications Analytical Toxicology - Colour tests methods | 6 Colour tests methods 45 Nitrous acid 45.1 Method 45.2 Indications 46 Palladium chloride 46.1 Reagent 46.2 Method 46.3 Indications 47 Phosphorus test 47.1 Method 47.2 Indications 48 Potassium dichromate 48.1 Method 1 48.1.1 Indications 48.2 Method 2 48.2.1 Indications 49 Schiff’s reagent 49.1 Reagent 49.2 Method 49.3 Indications 50 Scott’s test (see also cobalt thiocyanate test) 50.1 Reagent 50.2 Method 50.3 Indications 51 Simon’s test (modified sodium nitroprusside test): 51.1 Reagent 51.2 Method 51.3 Indications 52 Sodium dithionite 52.1 Reagent Analytical Toxicology - Colour tests methods | 7 Colour tests methods 52.2 Method 52.3 Indications 53 Sodium nitroprusside 53.1 Reagent 53.2 Method 1 53.2.1 Indications 53.3 Method 2 53.3.1 Indications 53.4 Method 3 53.4.1 Indications 54 Sodium nitroprusside–acetone 54.1 Reagents 54.2 Method 1 54.3 Method 2 55 Sodium picrate (Steyn test) 55.1 Reagent 55.2 Method 55.3 Indications 56 Sulfuric acid 56.1 Method 56.2 Indications 57 Sulfuric acid–fuming sulfuric acid 57.1 Reagent 57.2 Method 57.3 Indications 58 Tetrabromophenolphthalein ethyl ester 58.1 Reagent 58.2 Method 58.3 Indications Analytical Toxicology - Colour tests methods | 8 Colour tests methods 59 Thalleioquin test 59.1 Method 59.2 Indications 60 Trinder’s reagent (see ferric chloride) 60.1 Reagent 60.2 Method 61 Vanillin reagent 61.1 Reagent 61.2 Method 61.3 Indications 62 Zwicker reagent (alkaline cobalt test) 62.1 Reagent 62.2 Method 62.3 Indications Amalic acid test (test for xanthines) Method Add to the sample a few drops of 10 M hydrochloric acid followed by a few crystals of potassium chlorate, and evaporate the mixture to dryness. Observe the colour of the residue then add two or three drops of 2 M ammonium hydroxide and again observe the colour. Indications A red, pink, orange or yellow residue, which changes to pink, red or violet after the addition of ammonium hydroxide indicates the presence of a xanthine. Ammoniacal silver nitrate Analytical Toxicology - Colour tests methods | 9 Colour tests methods Reagent To 20 mL of 0.1 M silver nitrate add sufficient strong ammonia solution to dissolve the initial precipitate. Method Dissolve the sample in a minimum amount of water, with the addition of ethanol if necessary, add an equal volume of the reagent and note any colour that develops. Heat the mixture in a water–bath at 100° for 30 s. Indications Red, yellow, brown or black colours (especially at room temperature) indicate potent reducing power, which occurs when adjacent carbon atoms in a ring each bear a hydroxyl group. There is no response when the hydroxyl groups are meta to each other, but there is some restoration of reducing power when they are para to each other. Some colour production is also obtained with ethynyl bonds, but not with ethylenic bonds. Ethchlorvynol and ethinylestradiol both give a white precipitate that turns yellow on heating. Carbidopa gives a silver mirror on heating. Antimony pentachloride Reagent Dry some antimony trichloride over phosphorus pentoxide, melt the dried material (m.p. 73°), and pass dry chlorine gas into the melt until a yellow fuming liquid is obtained. Add this liquid to about ten times its volume of chloroform, filter the solution into a dark glass–stoppered bottle and store in a desiccator. Method Place one drop of an ethanolic solution of the sample on a filter paper, add one drop of the reagent and dry in a current of warm air. Alternatively, the test may be carried out by adding one drop of the reagent to the sample on a white tile. Analytical Toxicology - Colour tests methods | 10 Colour tests methods Indications Various colours are obtained with the cardiac glycosides, their aglycones and certain oestrogens and corticosteroids . No colour is obtained with beclometasone, cortisone, fluocinolone, fludroxycortide, prednisolone, prednisone, progesterone, testosterone or triamcinolone. Aromaticity Method 1 Place a portion of the sample in each of two ignition tubes, and to one tube add some solid sodium hydroxide. Heat both tubes carefully, allow the water vapour to escape, insert into the vapours in each tube an open capillary tube that contains Marquis reagent, and observe the colour of the reagent. Indications Red or orange colours indicate that the sample is aromatic in nature. The colours probably result from the liberation of traces of aromatic hydrocarbons, phenols, etc. Colours obtained after heating with sodium hydroxide generally indicate the presence of aromatic acids. Colours obtained after heating without sodium hydroxide generally indicate the presence of phenols, phenolic acids and aldehydes that contain more than one hydroxyl group. A negative result does not necessarily imply that the substance is non–aromatic. Method 2 Add two or three drops of nitric acid to the sample, heat in a water–bath at 100° for 1 min, cool the mixture, dilute three to four times with water and make the solution alkaline by the addition of a 40% (w/v) solution of sodium hydroxide. Indications A change from colourless or yellow in acid solution to darker colours (e.g. orange or Analytical Toxicology - Colour tests methods | 11 Colour tests methods red–orange) after the addition of sodium hydroxide indicates the presence of a benzene ring in the molecule, probably though the production of a nitrophenol or other nitro compound.