Chromogenic Subject

Abbasi [234] has described a spectrophotometric method employing N-p-methoxyphenyl-2,-furohydroxic acid for the determination of titanium in soils. In this method, the soil sample was subjected to alkali fusion. The ash was treated with nitric acid to adjust it to pH 2.0 and filtered prior to adjustment to 10 pM with respect to hydrochloric acid. Stannous chloride (5M) was added to the filtrate, and the chromogenic reagent was dissolved in chloroform. The chloroform extract was evaluated spectrophotometrically at 385 nm against the reagent solution as blank. Approximately 61 ppm of titanium was found in a soil sample by this method. 

In addition, these chromophores are very delicate molecules from an energy state perspective and should not be subject to detergents and other reactants such as sodium based complex salts. Although, it is possible (and actually easy) to return the chromophores of vision to the liquid crystalline state after extraction and purification, it is not easy to prevent conversion of the chromophores into their chromogens or similar retinoids. These decomposition products do not exhibit the resonance phenomena (and resulting spectral characteristics) no matter what state of matter they are in. 

AEG precipitates as an insoluble color substance when subjected to peroxidase and hydrogen peroxide. The color is a bright red and is often more intense than that achieved with DAB. It does not conflict with any endogenous pigments. The drawback to the use of this chromogen is that it is soluble in alcohol. This means that the tissue sections cannot be... 

Thus, the subject index for these 150 entries shows nothing of the kind of analytical method used. The titles are adequate for 92, and the abstracts for 122, papers. This means that one must examine the 28 papers for which no information is given. It is significant, too, that one fourth of the abstracts for the 24 photometric methods do not give the chromogenic reagent used. Consequently, if concerned with this detail, one must look up at least six more papers. 

Another interesting development has been the efforts to measure these serine proteases by electrochemical activity principals. A. B. Kabi has made available modified chromogenic substrates for this application. This subject will not be covered in this review but the reader is referred to the series of papers on this topic (C12). 

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