Spectrophotometric determination of iron in highly alkaline solution with 4-hydroxy-1,10-phenanthroline

4-Hydroxy-1,10-phenanthroline forms a stable tris-chelate with iron(II) in the range of alkalinity from pH 10 to 2M sodium hydroxide, with molar absorptivity 1.19 x 10(4) l.mole(-1).cm(-1) at 545 nm. The determination of iron is performed by adding the phenanthroline, stannous chloride, and iron-free sodium hydroxide to the sample to give pH > 13; stannite is the active reductant. Beer's law is obeyed over the iron concentration range from 1 x 10(-5) to 8 x 10(-5)M. Advantages over existing methods are the use of stannous chloride instead of sodium dithionite, which avoids the problem of turbidity, and the stability of the iron(II) chelate towards oxidation by air. The conditional reduction potential at pH 11 for the iron(III)/iron(II) complex couple is 0.39 V.