Adsorption-bonded azo reagents in chemical tests based on the principles of precipitation paper chromatography

The possibility of using three groups of azo compounds in chemical tests based on the principles of precipitation paper chromatography is considered. The first group consists of the reagents showing the highest affinity to cellulose (Congo Red, Brilliant Yellow, Stilbazo, Cadion IREA, Sulfarsazen, and Titan Yellow). These reagents are immobilized on paper and are not washed out of it in acidic, alkaline, and neutral solutions. The immobilization of the reagents results in a bathochromic shift of their absorption bands with respect to their solutions and enhances the acidic properties of the reagents. The second group comprises compounds that are immobilized on paper only in acidic solutions (mono- and bisazo derivatives of chromotropic acid: Arsenazo II, Arsenazo III, Orthanilic K, Sulfochlorophenol S, Chlorophosphonazo III, and Carboxyarsenazo). Their immobilization on paper does not lead to a shift in the absorption spectra and acidic properties. The third group consists of compounds that are immobilized on paper either in acidic or in alkaline solutions (Acid Chrome Dark Blue, Eriochrome Black T, Magneson KhS, and Eriochrome Blue Black R). They are absorbed by cellulose as free acids in acidic solutions and as sodium salts in alkaline solutions. Test procedures have been developed for the determination of acids; alkalis (0.1-100 mM); the total alkalinity of water (0.2-35 mM); the total acidity. of water (0.2-20 mM); Cd, Al, and Pb (1-200 mg/L); Al, Th, U, and Zr (0.5-200 mg/L); and the total hardness of water (0.05-40 mM). The length of the colored zone in test strips laminated into a polymer film and contacting the test solution through a narrow edge is the analytical signal. The relative standard deviation does not exceed 30%; the analysis time is 10-15 min.