Photometric Determination of Traces of Iron by Color-fading Reaction of Rhodamine 6G

In dil.H2SO4 solution,iodide ion was oxidized to iodine(present as I-3 in excess of iodide) by ferric ion.The anionic complex,I-3 in turn was reacted with color reagent rhodamine 6G,to form an ion association complex of RD6G+·I-3,leading to decoloration of the color reagent.Linear relationship between the magnitude of decrease in absorbance(ΔA) and the concentration of Fe(Ⅲ) was obtained in the range from 20 to 200 μg·L-1,when measured at the wavelength of 526 nm,which is the absorption maximum of rhodamine 6G in the reaction medium.Detection limit(3s/k) of the method was found to be 16.6 μg·L-1.Based on these findings,a new photometric method for determination of trace amounts of iron was proposed.In its application to the determination of iron in samples of Chinese harbal medicines,values of recovery and RSD′s(n=5) found were in the ranges of 96.7%-103.0% and 2.2%-4.7% respectively.