Optimized Ultrasound-Assisted Emulsification-Microextraction Followed by ICP-OES for Simultaneous Determination of Lanthanum and Cerium in Urine and Water Samples

In this study, optimized ultrasound-assisted emulsification–microextraction (USAEME) combined with inductively coupled plasma-optical emission spectrometry (ICP-OES) was applied to simultaneous determination of trace levels of lanthanum (La) and cerium (Ce) in water and biological samples. 5,6,14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadecane (a dioxa-diazamacrocycle) was used as chelating agent. Tetrachloroethylene was selected as extraction solvent. The effective parameters of USAEME including pH, salt effect, ultrasonic time, temperature, volume of extraction solvent, and concentration of the chelating agent were studied by a fractional factorial design to identify the significant parameters and their interactions. The results showed that pH and concentration of chelating agent were significant. In the next step, to optimize important parameters, a central composite design was performed. Under the optimal conditions (5.5 for pH and 180 mg L−1 for concentration of chelating agent) the calibration graphs were linear in the range of 0.1–1000 for La and 1–1000 µ g L−1 for Ce. The determination coefficients (R2) were 0.999 and 0.998 for La and Ce, respectively. The limits of detection were 0.012 for La and 0.61 µ g L−1 for Ce. The relative standard deviations (RSD %, n = 7) at 200 µ g L−1 were 3.5% for La and 3.1% for Ce. The method was successfully applied to the analysis of La and Ce in real water samples with the recoveries in the range of 93–99%