Dyes, General Survey

MUS 00] Mustroph H., Dyes general survey , Ullmann s Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH Co. KGaA, pp. 1-38, 2000. 

Time-resolved fluorescence spectroscopy is also a valuable tool in biological and medical research [10.143-147]. Since the lifetimes involved are normally short, picosecond spectroscopy techniques are frequently employed (Sect. 9.4). Examples of fluorescence decay curves for tissue recorded with delayed coincidence techniques employing a frequency-doubled picosecond dye laser are depicted in Fig. 10.42. The decay characteristics allow the discrimination between tumour and normal tissue, and atherosclerotic plaque and normal vessel wall, respectively. General surveys of the use of LIF for medical diagnostics can be found in [10.148,149]. 

According to the 1981-83 National Occupational Exposure Survey (NOES, 1997), approximately 100 000 workers in the United States were potentially exposed to hydroquinone (see General Remarks). Occupational exposures to hydroquinone may occur in its production and use in the production of dyes, paints, motor fuels and oils, and some polymers. Dermal contact with hydroquinone may occur in the development of black-and-white photographs. 

It has been necessary to understand the relationship between molecular fine structure of cyanine dyes and important properties such as colour, dye aggregation, adsorption on silver halide and electrochemical potentials in order to design and prepare sensitizers with optimum performance. For general discussion of these topics and the mechanism of spectral sensitization, the reader is referred to recent surveys on the subject (B-77MI11401, 77HC(30)441). 

The next logical step toward chromophore design was to conduct a spectral survey of commercially available organic compounds in order to learn some general structure-property relationships for minimization of the residual absorbance. As an easily measured figure of merit, the ratio between the minimum and maximum molar absorptivities has been used. In many cases, this ratio (expressed in percent, or more conveniently, as the minimum molar absorptivity per 100,000 L/mol-cm of maximum absorbance) is 5-10% (5000-10,000 per 100,000). (The lower the number the better the dye.) An improved figure of merit would take into account the area under the absorption curve as well as the location of the transparent window relative to the peak in the absorption. This is tantamount to calculating the dispersion from the absorption spectrum, which was too complex for this type of survey. 

This chapter gives a short survey on cationic dyes and shows typical representatives of each class of cationic dyes. In general, the dyes are classified according to their chemical structure. 

In this respect adsorption of dyes has been popular, especially because their colour allows rapid and accurate spectroscopic detection in the supernatant. However, caveats (i) and (il) above also apply to these adsorbates. For a discussion the reader may consult the proceedings of a symposium devoted to surface area determination in general containing a contribution by Padday in which the outcome of a comparative survey over 19 different laboratories was reported, dealing with the adsorption of the dye 1,1 - diethyl-2,2 cyanine on silver bromide and a few other adsorbents. Giles et al. have given a list of recommended a -values ... 

A survey of acute oral toxicity, as measured by the 50% lethal dose (LD j) test, demonstrated that of4461 colorants tested, only 44 had an LD-,j< 250 mg kg and that 3669 exhibited practically no acute toxicity (LD > 5 g kg ). The rest fell somewhere between these two levels. The evaluation of these colorants by chemical classification revealed that the most toxic ones were found among the diazo (mostly benzidine derivatives) and the cationic dyes. It is widely known that some general cationic compounds have toxic properties. Pigments and vat dyes by comparison were discovered to have extremely low acute toxicity - presumably due to their insolubility/very low solubility in water and in lipophilic systems. 

G. While area surveys are generally considered as passive surveys, i.e., actions taken based on survey results may be deferred for hours or days, personnel surveys are active, in that actions taken to remove contaminated materials from body surfaces are usually taken immediately. Because they are active surveys, the locations of the contamination on body surfaces are not usually plotted, as is the case in area surveys. Instead, contaminated areas are identified with tapes, dyes, magic markers, etc., on the body surface itself. 

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