Indigo test

Indigo test A dilute solution of indigo in concentrated sulphuric acid is added to the chlorate solution until the latter has a pale-blue colour. Dilute sulphurous acid or sodium sulphite solution is then added drop by drop the blue colour is discharged. The chlorate is reduced by the sulphurous acid to chlorine or to hypochlorite, and the latter bleaches the indigo. 

Indigo test no decolonization even in the presence of acid (difference from hypochlorite and chlorate). 

Formation of indigo test The test depends upon the conversion of acetone, formed by the dry distillation of acetates (see reaction 10), into indigo. No other fatty acids give this test, but the sensitivity is reduced in their presence. 

Acetate. Mix 20 mg of the substance with 1 ml of ethanol or n-butyl alcohol and 5 drops concentrated H2S04. Heat in the hot water rack for 10 minutes, and pour into 2 ml of Na2C03 solution - characteristic odour of ester (IV.35, 3) OR, better, indigo test (IV.35, 9). Mix 15 mg of the substance with 15 mg of CaC03 in a semimicro test-tube, introduce a pressure-filter tube carrying a strip of filter paper moistened with a solution of 5 mg of o-nitrobenzaldehyde in 1 ml of NaOH solution. Heat the test-tube strongly. Blue or green stain on paper confirms acetate. 

Acetate. Action of ethanol or of n-butyl alcohol and concentrated H2S04 (IV.35, 3) or indigo test (IV.35, 9) using ordinary test-tube or ignition tube. 

Tests using indigo have shown that reduction with alkaline hydroxyacetone is most reproducible when the concentrations are as follows [237] ... 

A simple qualitative test of the purity of the indigo obtained can be carried out as follows A little of the material is heated for some time (with shaking) in a test tube with pyridine and some drops of the liquid are then poured on to a filter paper. If the indigotin is pure the pyridine is not coloured, whereas impurities which may be formed when working on a small scale confer on it a more or less dirty brown colour, as shown by a spot test. If it is desired to purify the whole of the indigo with pyridine, the dye is collected at the pump after boiling with the liquid, washed with pure hot pyridine, boiled once more with hydrochloric acid, collected at the pump, washed with hot water, and dried.2... 

Experiment.1—Heat as much finely powdered indigo as amply covers the tip of a knife with about twice as much lead peroxide, a few granules of calcium chloride, and 5 c.c. of benzene in a test tube held in a boiling water bath for five minutes. Filter the reddish-brown solution obtained and divide the filtrate into two portions in test tubes. To one portion add quinol dissolved in very little alcohol, to the other dilute solution of stannous chloride in hydrochloric acid. The dehydroindigo is converted into the dye which separates in blue flocks. 

Indigo-Carmine Solution To a mixture of 10 ml of HC1 and 990 ml of a 20% w/v soln. of N2-free H2S04 in DW, add sufficient indigo-carmine (about 0.2 g) to produce a solution that complies with the following test Add 10 ml to a soln. of 1.0 mg of KNOs in 10 ml DW, rapidly add 20 ml HjSC and heat to boiling. The blue colour is just discharged in 1 minute. 

A simple spot test was used for the identification of procaine, and other drugs [30], The method uses one or more of the following reagents 0.4% Alizarin red S (C.I. Mordant Red 3) in 20% acetic acid, 0.3% indigo carmine (C.I. Acid Blue 74), 0.4% indigo carmine in 30% acetic acid,... 

Analysis. The colorimetric method for In is capable of a detection limit of 20 ppb. Indium or an In compound in the flame gives an indigo blue color (451.1 nm). This photon line allows for the spectrophotometric determination ofinby AAS (atomic absorption flame spectroscopy). The method is sensitive to about 300 ppb. With ETAAS, this limit drops to 10 ppb, as it does with ICPAES. ICPMS drops the limit to 0.01 ppb. Alizarin detects In, as well as Al, but the reaction with Al can be masked by addition of F to a spot test. The limit of detection is about 1 ppm. 

Chlorine Water and Its Properties. 1. Saturate 5-10 ml of distilled water with chlorine. Note the colour and odour (carefullyl) of the solution obtained. What substances are present in chlorine water Write the equation of the reaction and its equilibrium constant. Test how the obtained chlorine water affects an indigo solution and coloured fabric. What is observed What substance has a bleaching effect ... 

Quantitative Determination of Indigo Blue (Indigotin). — This test is to be carried out as detailed under Synthetic Indigo. 

Extraneous Organic Matter.—The powdered indigo is mixed to a paste with a little water if it gives a gluey or mucilaginous mass, gum or dextrin is present. If a little more water is added and the mass filtered, the filtrate may be tested for these substances. 

A vatted black (indigo and logwood). e> Fibre blue or blue violet, solution crimson. Test for indigo by extraction, evaporation, and sublimation. 

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