Synthesis and spectrophotometric studies of some benzothiazolylazo dyes - determination of copper, zinc, cadmium, cobalt and nickel

4-(2-Benzothiazolylazo)-2-amino-3-hydroxypyridine and its derivatives 4-(4-methyl-2-benzothiazolylazo), 4-(6-chloro-2-benzothiazolylazo) and 4-(6-bromo-2-benzothiazolyl-azo)-2-amino-3-hydroxypyridines have been synthesized. All these dyes are very sensitive chromogenic reagents for the determination of copper, cadmium, zinc, cobalt and nickel. The reagents react with the metal ions to form purple-coloured complexes (lambda(max) 540-570 nm) in aqueous acetone solution within the pH range 2.8 to 4.6. Copper can be selectively determined at pH 2.8 and most of the metal ions do not interfere except for nickel and cobalt. Cadmium, zinc, cobalt and nickel can be determined at pH 4-5. Their mutual interference can be eliminated using suitable masking reagents. A further advantage of this method is that an extraction procedure is not required and therefore the analytical procedure is very simple.