Direct Dyeing Principle

Conventional directdyes include monoazo, disazo. trisazo. and tetrakisazo dyes. It is advantageous to subdivide them according to the nature of their chemical structure. Disazo dyes, for example, can be divided according to chemical synthesis principles into primary and secondary. Conventional azo direct dyes further include symmetric urea derivatives, dyes obtained by oxidation of amines, and triazinyl and copper-containing dyes. 

In principle the anionic dyes also include direct dyes, but, because of their characteristic structures, these are used to dye cellulose-containing materials and are applied to the fiber from a neutral dye bath (see Section 3.3). 

Although a number of quantitative assays are available for allele frequency estimation, most are difficult and expensive to develop or implement. In this chapter, we describe the most versatile and least expensive assays for allele frequency estimation, namely, the template-directed dye-terminator incorporation assay with fluorescence quenching detection (the FQ-TDI assay [3]). The FQ-TDI assay is a real-time homogeneous primer extension assay based on two principles, namely, that deoxyribonucleic acid (DNA) polymerase catalyzes the allele-specific incorporation of a dye-terminator at the polymorphic site and that the fluorescence intensities of a fluorescent dye decreases significantly when it is incorporated into primers. 

The initial objective of this series of books has been to establish a coherent body of explanatory information on the principles and application technology of relevance for students preparing to take the Associateship examinations of the Society. This particular book has been directed specifically to the subject areas covered by Section A of Paper B the organic chemistry and application of dyes and pigments and of the auxiliaries used with them in textile coloration processes. However, many qualified chemists and colourists interested in the properties of colorants and their auxiliaries have found the First Edition useful as a work of reference. For several reasons it has been convenient to divide the material into two separate volumes 1. Colorants, 2. Auxiliaries. Although fluorescent brighteners share some features in common with colorants, they have been treated as auxiliary products in this book. 

NIR and visible molecular probe dyes utilize the same principle changes in the microenvironment of the probe molecule induced by an analyte can be directly measured by spectral changes. The measured changes are dependent upon the concentration of the analyte and the extent of interaction between the dye and the analyte however, the spectral properties of the dye determine the magnitude of the signal. 

Various phthalein dyes have been proposed for detection and determination of H2O2, with different operating principles, such as direct measurement of the dye and complex formation. The FOX assay is based on the oxidation of Fe(II) to Fe(III), followed by complex formation of the latter ion with Xylenol Orange (71). The concentration of the complex is measured at = 560 nm (e = 4.3 x 10 The linearity... 

Wavelength dependence of detector response can also be compensated by using a fluorescent screen in front of the photocell or photomultiplier. This screen acts as a quantum counter. A concentrated solution of Rhodamin B in glycerol (3g per litre) or fluorescein in 0.01N NajCO, has been used for this purpose. Quantum counters work on the principle that whatever be the wavelength of radiation incident on the screen, if completely absorbed, the photodetector sees only the wavelength distribution of fluorescence from the dye. It requires that the fluorescence yield of the counter material be independent of wavelength of excitation and therefore that its emission intensity is directly proportional to the incident intensity. 

There are a number of yellow substantive dyes synthesized by this principle. Example C. I. Direct Yellow 41, 29005 [8005-53-6] (29) is obtained by phosgene treatment of an equimolar mixture of bases A (sulfanilic acid— cresidine) and B (jt>-nitroaniline—> salicylic acid and reduction of the N02 group). The mixture additionally contains the two corresponding symmetrical dyes. 

Color Strength, Hue, Chroma [20, p. 99-105], The coloring properties of a dye are assessed by preparing a dyed test sample whose color is evaluated. This must, in principle, always be done by the human eye because color perception, being a subjective sense impression, is not accessible to direct measurement. However, with the aid of colorimetry this visual perception can be represented more or less closely by measurable quantities. Since colorimetry is an objective method and is therefore more accurate and reproducible than subjective visual assessment, it is veiy widely used today. Color is a three-dimensional quantity and must therefore be expressed by a set of three numbers (color coordinates). In practice, these are typically the values of color strength, hue, and chroma. 

A limited set of phenylenediamine color developers are used. Kodak s CD-3, CD-4, and CD-6 (26-28) are the principle color developers used today [31], They are directly incorporated into the alkaline processing fluid. The methyl group in the 2-position is important for preventing side reactions and enhancing the formation of the desired dye. The phenylenediamine undergoes a two-electron oxidation to quinonediimine, which then reacts with the color couplers to form the desired chromophores [32],... 

Dyes such as benzidine-based dyes which are classified as carcinogens, mutagens, or teratogens according to the Directive 67/548/EEC (CMR substances, Table 8.3), are subject of the Council Directive 76/769/EEC (Restrictions on the Marketing and Use of Certain Dangerous Substances and Preparations) and must not be marketed as such or in preparations if they contain more than the maximum concentration of 0.1%. In principle, the directive does not ban the import of articles , e.g., textiles dyed with benzidine-based dyes, because articles are not covered by the directive. 

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