Naphthalene black

The presence of free bromine, and consequently the end-point, can be detected by its yellow colour, but it is better to use indicators such as methyl orange, methyl red, naphthalene black 12B, xylidine ponceau, and fuchsine. These indicators have their usual colour in acid solution, but are destroyed by the first excess of bromine. With all irreversible oxidation indicators the destruction of the indicator is often premature to a slight extent a little additional indicator is usually required near the end point. The quantity of bromate solution consumed by the indicator is exceedingly small, and the blank can be neglected for 0.02M solutions. Direct titrations with bromate solution in the presence of irreversible dyestuff indicators are usually made in hydrochloric acid solution, the concentration of which should be at least 1.5-2M. At the end of the titration some chlorine may appear by virtue of the reaction ... 

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. 

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.)... 

Naphthalene black 12B 405 l,2-Naphthaquinone-4-sulphonic acid sodium salt 705... 

Using an acrylamide-gel as support, Coombe- 0 has demonstrated the quantitative assay of neomycin with a recovery of 96% in the presence of bacitracin and polymixin. In this case quantitation was achieved by densitometry after staining the gel with naphthalene black. 

Black smoke Aluminum powder. Smokeless powder. Naphthalene Black powder. Potassium nitrate. Coal tar. Charcoal powder. Black smoke produced, Screening/signaling smoke ... 

A very interesting difficulty is the difference in dye uptake between a concentrated and a diluted protein fraction. Eberhard (El) gave a careful account of naphthalene black evaluation of spots of chemically pure albumin and 7-globulin. He found that, in photometric measurements on the eluates of the stained fractions, those which were distributed over a large area of paper always gave lower values than fractions eluted from a smaller area of paper, although the total amount of protein was actually the same. Difficulties of photometry on paper were excluded by this technique, and Eberhard considered that there is competition between paper and protein for the same dye molecule. It is, perhaps, easier to find the key in the quantity of salt, which is greater in the diluted than in the concentrated fraction. The same phenomenon occurs with bromophenol blue (G25). 

Fig. 37. Relationship between photometer reading and protein concentration. The protein was contained in circular areas approximately 16 mm in diameter and the photometer readings are those corresponding to the central portion of each area. Dyes Curve A, light green Curve B, bromocresol green Curve C, naphthalene black (04).

For naphthalene black there is a perfect eluant, composed of equal parts ethanol and 0.5 N sodium hydroxide. The alkaline pH and the ethanol are required to overcome adsorption of protein to paper, but as alkaline solutions of the dye are very unstable, probably due to the presence of traces of heavy metal ions, the addition of 500 mg of Com-plexon (EDTA) per liter is required (D3 Fig. 26). In this condition an alkaline solution of amido black is stable for indefinite periods of time. 

Figure 2.15. The real form of the four frontier MOs of [10]annulene. The doubleheaded arrows indicate the cross-links that produce naphthalene (black arrows) and azulene (white arrows), respectively. First-order shifts are shown as vertical arrows on the orbital energy levels in the center (by permission from Michl, 1984).

Naphthalene Black D C.I. acid black 7 Coomassie Brilliant Blue R Coomassie Green T Coomassie Fast Grey G Coomassie Navy Blue G Viscolan Black B Sulphonine Red 3B... 

In the dye procedure, the globulin fraction is isolated by ammonium sulfate precipitation, and allowed to react with naphthalene black in a citric acid buffer. The stained globulins are then separated by centrifugation, and the amount of dye in the supernatant fluid is measured in a colorimeter (Pll). The resulting loss of soluble dye is related to the globulin concentration, and the procedure is standardized with pure 7-globulin. 

Amido black lOB (Bayer), or naphthalene black 12B.200 (ICI), or Pontacyl blue black SX (Du Pont), or Buffalo black (National Aniline) are most often used for routine processes. One-half gram of one of these dyes is dissolved in a solution of 5.0 g mercuric chloride and 5.0 ml acetic acid in 100.0 ml distilled water (W4). The solution is filtered before use. The staining of the slides with the agar film is done in the ordinary tray used for microscopy and takes 5 min. For differentiation, the slides are rinsed in a 2 /c solution of acetic acid in distilled water or in a water solution of 50 % methanol and 10 % acetic acid. The bath is renewed until the background is colorless. Often, new lines of precipitate show up at this stage. The slides are finally washed in water and dried within a few minutes. 

Alternatively naphthalene black 1213200 is used. The paper is allowed to dip into a saturated dye solution m methanol and 10% acetic acid. After 10 minutes the paper is washed several times with methanol containing 10% acetic acid. 

The equivalence point may also be detected by using color indicators (methyl orange, methyl red, naphthalene black, xylidine ponceau, and fuchsine), which exhibit their usual color before the equivalence point and after become discolored by an irreversible chemical transformation. The transformation may be an oxidization of the indicator or a fixation of bromine on it, since it is generated once the equivalence point is reached. In hydrochloric acid, which is the most commonly used medium, we may consider that after the equivalence point, bromate ions oxidize chloride ions [ii°(Cl2/Cr) 1.38 V] according to the reaction... 

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