Amino acid specific color formation

In spite of the lack of specificity of the method, it is obvious that amines which give a color by Richter s method (48) are usually increased in chronic hypertension, especially in the more severe forms. Because the more highly active phenolic amines are not measured by this method, and others might be present in too small amounts to measure, these results may be taken as a manifestation of a general disturbance of amino acid metabolism in chronic hypertension which may include the formation of pressor amines it does not prove their presence. 

Selective reagents form colored or fluorescent compounds on a group- or substance-specific basis and aid in compound identification. They also allow the use of a thin-layer chromatography (TLC) system with less resolution because interfering zones will not be detected. Examples include the formation of red to purple zones by reaction of a-amino acids with ninhy-drin, detection of acidic and/or basic analytes with the... 

The thiobarbituric acid (TBA) value test is a popular way of measuring rancidity in certain foods and oxidation products in biological systems. It is based on the formation of a colored complex between two molecules of TBA and one molecule of malonaldehyde resulting from thermal decomposition of polyunsaturated peroxides. This reaction is not specific due to the presence of many TBA-reactive substances (TBARS), such as browning reaction products, protein and sugar decomposition products, amino acids, nucleic acids and nitrite. 

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