Simplex optimisation of a flow injection analysis (FIA) system to determine Rare Earth Elements (REE) with Arsenazo III

A Flow Injection Method (FIA) for the determination of Rare Earth Elements (REE) in mixed solutions is described and the parameters involved are optimised mathematically by a modified simplex method (MSM). The performance of the system permits the determination of REE from solutions with pH's ranging from 0 to 6. A linear calibration range of up to ca. 30 mg L-1 for an injection volume of 70 μL and a concentration of Arsenazo III equal to 1.22 mM is achieved representing a tenfold increase over previously reported values. The detection limit of the method is 0.70 mg L-1 for all the elements studied except Yb which is less sensitive (1.27 mg L-1). In the case of Yb, an increase in the linear range of up to ca. 40 mg L-1 is achieve. The FIA method can be applied in the analysis of mixtures containing different pairs of REE elements with a relative error of less than 5%.