Determination of melamine in soil samples using surfactant-enhanced hollow fiber liquid phase microextraction followed by HPLC-UV using experimental design

Surfactant-enhanced hollow fiber liquid phase (SE-HF-LPME) microextraction was applied for the extraction of melamine in conjunction with high performance liquid chromatography with UV detection (HPLC-UV). Sodium dodecyl sulfate (SDS) was added firstly to the sample solution at pH 1.9 to form hydrophobic ion-pair with protonated melamine. Then the protonated melamine-dodecyl sulfate ion-pair (Mel-DS) was extracted from aqueous phase into organic phase immobilized in the pores and lumen of the hollow fiber. After extraction, the analyte-enriched 1-octanol was withdrawn into the syringe and injected into the HPLC. Preliminary, one variable at a time method was applied to select the type of extraction solvent. Then, in screening step, the other variables that may affect the extraction efficiency of the analyte were studied using a fractional factorial design. In the next step, a central composite design was applied for optimization of the significant factors having positive effects on extraction efficiency. The optimum operational conditions included: sample volume, 5 mL; surfactant concentration, 1.5 mM; pH 1.9; stirring rate, 1500 rpm and extraction time, 60 min. Using the optimum conditions, the method was analytically evaluated. The detection limit, relative standard deviation and linear range were 0.005 mu g mL(-1), 4.0% (3 mu g mL(-1), n=5) and 0.01-8 mu g mL(-1), respectively. The performance of the procedure in extraction of melamine from the soil samples was good according to its relative recoveries in different spiking levels (95-109%). (C) 2014 Production and hosting by Elsevier B.V. on behalf of Cairo University.