SOLID-PHASE EXTRACTION-PHOTOMETRIC DETERMINATION OF IRON(Ⅲ)IN WATER SAMPLES USING THE REAGENT 5,7-DIBROMO-8-HYDROXYQUINOLINE (DBHQ)

In an NH4OAc buffer medium of pH 7.0 and in the presence of CTMAB,DBHQ reacts with Fe(Ⅲ) to form a stable coordination complex with mole ratio (R∶Co) of 3 to 1.The colored complex was concentrated on Waters Sep-Park C18 solid-phase extraction column by passing the sample solution through the column at a flow-rate of 10 mL·min-1.The solution remained in the column was removed by centrifuging the extraction column.The Fe(Ⅲ)-DBHQ complex was then eluted from the column with 2.0 mL of ethanol at a flow-rate of 5 mL·min-1.The eluate was transferred to an absorption cell with appropriate light-path,and the absorbance was measured at 610 nm,the λmax of the colored complex,using reagent blank as reference solution.It was found that most of the common co-existing ions in water sample have no absorption at this wavelength,hence do not interfere with the determination of Fe(Ⅲ).Beer′s law holds in the range of 0-5 μg per mL of solution,with a molar absorptvity of 7.24×103L·mol-1·cm-1.In its application to the analysis of water samples,RSD′s of less than 3% were obtained.Recoveries were found in the range of 97%-103%.