Dual energy computed tomography (CT) has been previously shown to be capable of quantifying iron concentration in a phantom model. In this work, a commercial three material decomposition algorithm was investigated with the aim of quantifying iron concentration in vivo with dual energy CT. Iron (III) nitrate solutions of five/seven different concentrations were placed in syringes of two different cross-sectional areas within anthropomorphic phantoms of three different sizes and scanned using various x-ray tube potentials and beam filtration levels. A commercial three material decomposition software package was used to measure iron concentration values in specified regions of interest. These data were used to assess the effects of tube potential, beam filtration, phantom size, and object size on the ability of dual energy CT to accurately quantify iron concentration. The object's cross sectional area (diameter of syringe containing the iron solution) affected the accuracy of the iron quantification, with measurements averaged over a larger region of interest having improved accuracy. In most cases, the greater spectral separation afforded by the tin filtration improved the accuracy of the iron quantification. Using the larger syringes (approximately 100 mm2 cross sectional area) and small phantom size, dual energy CT measurements of the three highest iron concentrations (approximately 10-18 mg/ml) had a maximum percent difference from the known value of 21%.