Indirect determination of iodine by cold vapour atomic-absorption spectrophotometry utilising the interfering effect of iodine against mercury. Part I. General study and application to the determination of iodine in seaweed

Abstract

A simple and rapid method is described for the indirect determination of iodine as an interferent against mercury in cold vapour atomic-absorption spectrophotometry. The interference effect is due to the formation of mercury(II) iodide complexes, which in highly acidic solutions cause a decrease in absorbance for mercury(II) proportional to the amount of iodine present. Within certain concentration limits a straight-line calibration graph is obtained, making the determination of small amounts of iodine possible. The detection limit is 2.5 ± 0.7 µg of iodine if it is allowed to interfere (as iodide or iodate) against 100 ng of mercury(II) in 3.0 M nitric acid solution. Interferences for the method are, in general, the same as in the cold vapour atomic-absorption determination of mercury. Chloride and moderate amounts of bromide do not interfere. The possible interference of certain metals, especially the noble metals, is discussed. The proposed method has been used with satisfactory results in the determination of iodine in a seaweed sample (Ascophyllum nodosum) that had been analysed earlier by neutron activation analysis.