Spectrophotometric determination of tin in steels with 2-(5-nitro-2-pyridylazo)-5-[N-n-propyl-N-(3sulfopropyl)amino]phenol

A highly sensitive azo dye, 2-(5-nitro-2-pyridylazo)-5-[N-n-propyl-N-(3-sul fopropyl)amino]phenol (Nitrro-PAPS), is used as a colorimetric reagent for the determination of tin(IV) content. Nitro-PAPS reacts with tin(IV) to for m a water-soluble complex in 1.0 M acetic acid. Full color development is a ttained within 5 minutes, and maintains constant absorbance for at least 24 hours. The apparent molar absorptivity is 7.7 x 10(4) dm(3) mol(-1) cm(-1) at a maximum wavelength of 580 nm. Beer's law is obeyed for tin(IV) in the range of 0-1.2 mug ml(-1). The proposed method is successfully applied to the determination of trace amounts of tin in steels.