The main parameters that affect CPE and signal measurements were evaluated by using an iron(III) reference solution (Fig. 2) and the evaluated intervals and selected values are shown in Table 2. Triton X-114 concentration is a critical parameter because both blank and analytical signals increased with the surfactant amount (Fig. 2a). While low Triton X-114 concentrations hindered the extraction efficiency, high amounts caused dilution of the SRP and increased the blank values due to light scattering. The analytical response was not significantly different from 1.5 to 3.0% Triton X-114 and the lowest value was selected to minimize the blank values and waste generation. The optimized concentration is 26-fold higher than the critical micelle concentration (0.35 mmol L−1) [22], then assuring the surfactant excess required for CPE. In the proposed procedure, the surfactant was added to the reagent solution to avoid the additional sample treatment required in previous works [4], [5] and [7].