DETERMINATION OF IRON BY FLOW-INJECTION BASED ON THE CATALYTIC EFFECT OF THE IRON(III) ETHYLENEDIAMINETETRAACETIC ACID COMPLEX ON THE OXIDATION OF HYDROXYLAMINE BY DISSOLVED-OXYGEN

A flow injection (Fl) spectrophotometric method for the determination of Fe based on the catalytic effect of the Fe(III)-ethylenediaminetetraacetic acid-complex on the oxidation of hydroxylamine by dissolved oxygen in a basic medium is described. The Fl manifold used was interfaced to a personal computer provided with appropriate software for automatic commanding of sample injection and data acquisition and processing. The absorbance response provided by the spectrophotometer was linear over the range 3.5-150 ng ml-1 of Fe, and the detection limit achieved was 2 ng ml-1, with a relative standard deviation of 2.4% for 50 ng ml-1 of Fe(III) (n = 11) and 6.7% for 5 ng ml-1 of Fe(III) (n = 11). The only serious interferences with the determination were those of Co(II), Cr(III) and Cu(II), but these could be reduced such that at 40, 40 and 10 times the Fe concentration they had no effect. The results provided by a normal and a reversed Fl configuration were compared and the method was satisfactorily applied to the determination of Fe in natural waters and white wine at a sampling rate of 60 samples h-1.