Synthesis of 3,5-bis(4-phenylazophenylaminodiazo) benzoic acid and its colour reaction with nickel

A new chromogenic reagent 3,5-bis(4-phenylazophenylaminodiazo) benzoic acid(BPAAD) is synthesized and its color reaction conditions with Ni(Ⅱ) are studied.In the buffer solution of Na2B4O7-NaOH at pH 10.0 and in the presence of TritonX-100,the chromogenic reagent reacts with nickel(Ⅱ) to form a red complex(2∶1).The maximum absorption wavelength of the complex is at 500 nm,and the apparent molar absorptivity is 1.46×105 L·mol-1·cm-1.Beer's law is obeyed in the range of 0～0.8 μg for nickel(Ⅱ) in 25 mL.The conditions for determining nickel and the effects of coexistent ions on the determination are examined.Adding masking reagent,the allowable amounts of Al3+,Fe3+,Cu2+,Hg2+,Cd2+ are increased.This method has been used for the determination of nickel in aluminum alloy samples with RSD of 2.5%-3.8%(n=5) and the results are agreement with those obtained by atomic absorption spectrometry.