Spectrophotometric determination of a small amounts of iron(II) using α, β, γ, δ-tetraphenylporphine trisulfonate

Abstract

α, β, γ, δ-Tetraphenylporphine trisulfonate (TPPS) reacts with iron(II) to form complex of the 1 : 1 molar ratio between TPPS and iron(II). The complex is stable in the pH range of 3.9 to 4.2 and the apparent stability constant is 7.2 as logK at pH 4.0 and ionic strength 0.010. Iron(II) in the range of (1.09.0) μg/50 ml is determined and the sensitivity is 0.48 ngFe(II) cm^-2 for 0.001 absorbance, and the molar absorption coefficient is 1.4 ×10⁵ dm³ mol^-1 cm^-1. Because iron(III) reacts with TPPS in the presence of L-ascorbic acid as a reductant, iron (II) and (III) are successively determined using L-ascorbic acid. Many cations, such as Mn(II), Co(II), Cu(II), Zn(II), Pd(II), Sn(II), etc. interfere on the equivalent mole of iron(II). Take 10 ml of the sample solution containing (1.09.0) μg of iron(II) into a 50-ml Erlenmeyer flask, and add 5 ml of 0.1 M acetate buffer solution to adjust pH to 3.94.2, and 5 ml of 5×10^-5 M TPPS solution. Immerse the flask in a boiling water bath for 150 min and cool to room temperature. Transfer the solution in the flask into a 50-ml measuring flask and dilute to the mark with water. Measure the absorbance at 395 nm against water.