The hydroxytriazenes 1-2 are used for the determination of transition metals. We report here application of a similar compound, phenylazo-bis- acetoxime (PABA) for spectrophotometric determination of iron(III). Phenylazo-bis-acetoxime was prepared by reported method 3 Stock Solution A 1.0 ×10 -2 M ferric nitrate nonahydrate (BDH) was prepared in distilled water and to prevent hydrolysis few drops of ( 1 M) concentrated nitric acid were added to it. The solution was standardized with EDTA. A 1x 10 -2 M solution of the reagent PABA was prepared in acetone. Tris- buffer (2%, v/v) was prepared. A UV./VIS. Systronic 108 Spectrophotometer and a Systronic 324 pH meter were used. Method Spectrum of phenylazo-bis-acetoxime was measured in the wavelength region 360-460nm against solvent blank. Iron and PABA solutions were taken in 1:5 ratio and the spectrum of iron complex was recorded against reagent blank in the range 360-460 nm. The working wavelength was found to be 362 nm. A set of solutions containing Fe(III) and Oriental Journal of Chemistry Vol. 24(3), 1161-1162 (2008) Analytical application of phenylazo-bis-acetoxime in the spectrophotometric determination of Iron (III) SABA KHAN* and REHANA KHANAM Department of Chemistry, M. L. Sukhadia University, Udaipur - 313 001 (India) (Received: August 18, 2008; Accepted: September 24, 2008) ABSTRACT Phenylazo-bis-acetoxime has been used for spectrophotometric determination of Iron (III) at 362nm, keeping the pH at 3.5-4.0. Beer’s law is obeyed in the range (4 to 24)x10 -5 M. The molar absorptivity and Sandell’s sensitivity values are 1,852 dm 3 mol -1 cm -1 and 30.15 ng cm –2 , respectively. Key words: Arylazo-bis-acetoxime, spectrophotometric determination, Iron (III). PABA reagent in ratio 1:5 was prepared and pH was varied between 2 to 6. The pH range of constant maximum absorbance was found to be between 3.5 to 4.0. Composition of the complex was determined by Job’s method and moles ratio method of Yoe and Jones. The study revealed that composition of iron(III) complex is 1:2 (M:R). Absorbance of set of six solutions containing Fe(III) to PABA in ratio 1:5 was measured at corresponding working wavelength against reagent blank. Beer’s law was obeyed in concentration range 4x10 -5 to 24x10 -5 M. Interference of 23 cations and anions in the determination of iron was studied. To the set of solutions containing iron to reagent 1:5 ratio, 10 ppm of different foreign ions were added at optimum conditions. Absorbance was measured against reagent blank. Those ions, which did not interfere at 10 ppm level their interference was again studied at 50 ppm level. In case no or little change in absorbance was seen as compared to the absorbance without any foreign ion, then for those ions interference was studied again at 100 ppm level. However tolerance of still higher concentration was not studied.