在稀硫酸介质中,Fe3+氧化I-成I2,I2与过量的I-结合生成I-3阴离子,I-3阴离子与罗丹明6G形成离子缔合物,导致罗丹明6G吸光度降低.在罗丹明6G的吸收峰526 nm波长下测定时,Fe3+的质量浓度在20~200 μg·L-1范围内,反应体系吸光度的降低值与Fe3+的质量浓度呈线性关系,方法的检出限(3s/k)为16.6 μg·L-1.据此建立了褪色光度法测定Fe3+的方法.用于中草药中微量铁的测定,回收率在96.7%~103.0%之间,相对标准偏差(n=5)在2.2%~4.7%之间.

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.