Spectrophotometric determination of dissolved oxygen with tris(4,7-dihydroxy-1,10-phenanthroline)iron(II)

Tris(4,7-dihydroxy-1,10-phenanthroline)iron(II) reacts rapidly and quantitatively with dissolved oxygen in alkaline aqueous solution. In ammoniacal solution, the reaction is accompanied by the disappearance of the intense red colour of the iron(II) compound, which gives way to the pale gray, slightly-dissociated ion tris(4,7-dihydroxy-1,10-phenanthrolinefiron)(III). By measurement of the absorbance of a solution containing the ferrous compound before and after the injection of an oxygen-containing solution, the concentration of dissolved oxygen in the sample can be accurately determined in the range 1-20 ppm.