Complexation with cationic dyes

The micro-scale extraction method utilizes the ability of anionic surfactants to form ion-pair complexes with cationic dyes such as methylene blue. These complexes behave as if they are neutral organic molecules. These ion pairs are easily extracted into a nonpolar solvent, thus imparting a color to the extract. The intensity of the color becomes proportional to the concentration of the surfactants in accordance with the Beer-Lambert Law of Spectrophotometry. 

Problems with the compatibility of the dyes can also arise in dyeing mixtures of PA and PAC fibers. Such blends are produced, e.g., for skiwear. The cationic dyes used for the PAC component do not dye normal PA fibers. Acid and metal-complex dyes leave PAC fibers practically white. Sulfo group containing 1 1 metal-complex dyes possess a zwitterionic character and therefore can be applied in low concentration in the same bath with cationic dyes, without the occurrence of precipitation. In this manner, one-bath dyeing can be carried out. The stability of... 

The nitrogen assumes cationic properties and forms a complex with the dye anion. The non-ionic ethylene oxide condensate portion of the molecule keeps the addition product in a state of solution. The wool has no affinity for the dye anion which is comple.xed with the nitrogen atom at low temperatures. As the liquor becomes hotter the dye anions are gradually released. Not only does it follow that the dye becomes available at a steady and slow rate, but also the release takes place at higher temperatures when the fibre is more swollen and the dye aggregates are broken down. 

The same approach was used to increase extraction of ion associates of complex metal anions with cationic dyes as in the case of cadmium iodide complexes Cdls with such dyes, used in photometric analysis. Cdl3(TBP) is extracted readily by benzene (19). 

Flotation reagent can react with dye to form colored complex. Absorbance of colored complex is in proportion to the concentration of reagent. Therefore, dye-reagent complex formation had been widely used for the testing process of alkyl sulfonate, sulfate, fatty acid, and fatty amine. The common color dyes consist of methylene blue, pinacyanol, bromophenol blue, methyl green, and eosin. In general, anionic collector is colored with cationic dye (such as methylene blue and pinacyanol). And anionic collector is colored with cationic dye (such as eosin). 

Cationic groups within a polymer can be quantified by colloid titration. A dye, such as orthotoluidine blue, is added to a dilute solution of the cationic polymer. Upon titration with potassium polyvinyl sulphate the cationic polymer forms a complex until the entire polymer is used up. At this point the additional potassium polyvinyl sulphate forms a complex with the dye and there is a colour change from blue to pink. 

Triphenylformazan behaves as a bidentate ligand forming 2 1 complexes (217) with divalent copper, nickel, and cobalt.377 Formazan metal complexes can be compared to complexes of azo dyes or beta diketones due to structural similarity.301,302 In general, formazan metal complexes have low stability toward acids. However, when electron-donating substituents are added to the aromatic ring, a considerable enhancement in stability is observed. Cationic complexes of type 218 are also known. The complexation of formazan with metal cation can be accompanied by oxidation to the tetrazolium salt and the formation of a complex... 

BASIS OF MANUAL PHOTOMETRIC TITRATION. The determination of anionic surfactants by a photometric titration employs a cationic indicator to form a coloured complex with the surfactant which is insoluble in water but readily soluble in chlorinated solvents (1 ). The end point of the titration occurs when there is a loss of colour from the organic phase. A considerable improvement in this technique is achieved by the use of a mixture of anionic and cationic dyes (4 ), for example disulphine blue and dimidium bromide (Herring s indicator (3)). The sequence of colour changes which occurs during the two phase titration of an anionic surfactant (AS) with a cationic titrant (CT) using a mixed indicator consisting of an anionic indicator (AD) and cationic indicator (CD) is summarised in Scheme 1 ... 

The complexation of neomycin with anionic dyes such as amaranth (F.D. C. Red No.2) is well knownl00,102 and has been made the basis of a quantitative assay for neomycinl°2,25. These complexes are again of the cation/anion type and their formation is dependant on the ionic strength of the solution. 

Dichromate anions are readily absorbed under acidic conditions by wool that has been dyed with chrome dyes. The chromium(VI) on the fibre is then gradually reduced by the cystine residues in wool keratin to chromium(III) cations, which react with the dye ligands to form a stable complex. In this way the cystine disulphide bonds are destroyed, resulting in oxidative degradation of the wool fibres [71]. 

Kimerle [27] reviewed the ecotoxicology of LAS focusing on the results rather than on the method of analysis, for which the author referred to the review undertaken by Painter and Zabel [30], alluding only to two papers on biota sample preparation. Litz et al. [31] determined the concentration of LAS in rye grass by Azure A active substances (AzAAS). AzAAS is a non-specific colorimetric method, which has not been used as frequently as MBAS (see Chapter 3.1). Briefly, it consists of the formation of an ion association complex with a dyed solution of Azure A (cationic). The complex formed is solvent-extractable and is separated from unreacted dye prior to colour measurement. 

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