Preparation and characterization of iron(iii) nitrilotriacetate complex in aqueous solutions for quantitative protein binding experiments

Various preparations of iron(III) nitrilotriacetate (FeNTA) solution reported in the literature lack a comprehensive method for accurate determination of FeNTA concentration and often result in unstable solutions. A detailed procedure for the preparation of FeNTA solution is presented that includes the standardization of both components of the chelate. The standardization of the components allowed the accurate determination of the molar absorption coefficients for the calculation of the FeNTA concentration in two different buffers at pH 5.6 and 7.4. The variation of pH in this range or ionic strength in the range from 0 M to 3 M (KCl) has little effect on the value of the molar absorption coefficient. The precise concentrations of all species involved in the equilibria between Fe and NTA were determined in the pH range 2-12 using the Jenkins–Traub algorithm to solve the 5th-order polynomial in Microsoft Excel. In view of the experimental observations and the calculated distribution of species, the stability of FeNTA solutions may be affected by the Fe : NTA ratio and the total concentrations, with dilute solutions and those with an excess of NTA over Fe showing higher stability.