Optimized Ultrasound-Assisted Emulsification-Microextraction Followed by ICP-OES for Simultaneous Determination of Ytterbium and Holmium in Natural Water

In this study, the optimized ultrasound-assisted emulsification-microextraction followed by inductively coupled plasma-optical emission spectrometry was applied to simultaneous extraction and determination of holmium (Ho3+) and ytterbium (Yb3+) in water samples. 1-(2-Pyridylazo)-2-naphthol was used as chelating agent to form extractable complexes. Volume of extraction solvent, concentration of chelating agent, pH, ultrasonic time, temperature, and concentration of salt were considered as the variables of the method. To evaluate the results, extraction recovery was selected as the response. Significance of the variables was investigated by using a half-fraction factorial design (2(f-1)) and the optimization was performed by applying a central composite design. The calibration graphs were linear in the range of 4-200 mu g L-1 for Ho3+ and 3-500 mu g L-1 for Yb3+ with determination coefficients (R-2) of 0.988 and 0.997 for Ho3+ and Yb3+, respectively. Limit of detection was 0.364 mu g L-1 for Ho3+ and 0.252 mu g L-1 for Yb3+. The relative standard deviations (C = 200 mu g L-1, n = 6) were in the range of 4.2-4.5%. The method was successfully applied to the analysis of real water samples with the recoveries in the range of 80-95%.