Simple and selective spectrophotometric method for the determination of iron (III) and total iron content, based on the reaction of Fe(III) with 1,2-dihydroxy-3,4-diketocyclo-butene (squaric acid)

Squaric acid (1,2-dihydroxy-3,4-diketo-cyclobutene) is used in a specific reaction with Fe(III) for the spectrophotometric determination of Fe(III) and total iron content. The optimization of the experimental parameters leads to the establishment of a simple, fast and accurate analytical method. The analytical procedure includes mixing ammonium squarate (40 mM), prepared in a phthalate buffer solution of pH 2.7, with the sample and measuring the absorbance at 515 nm. The molar absorptivity of the colored product is 3.95x10(3) L.mol(-1).cm(-1), at 515 nm. Calibration graphs for Fe(III) are rectilinear for 0.5-20 mgL(-1), with a detection limit of 0.3 mgL(-1) and r.s.d. not exceeding 2.5%, for five replicates of a 3.0 mgL(-1) standard solution. The method has been successfully applied to the determination of iron (III) and the total iron content after quantitative oxidation of iron (II). The results for several analyzed samples when compared with those acquired by using the FAAS technique, were found to be in satisfactory agreement. Microchimica Acta