To study the effect of extraction solvent volume on the extraction efficiency in DLLME-SFO method, different volumes of 1-undecanol (30, 40, 50, 60 and 70 l) containing 300 l of acetonitrile were tested to select the optimum volume of extraction solvent to be applied in subsequent experiments. All experiments were performed in triplicates (n = 3). According to the results in Fig. 2, the extraction recoveries decreased when the volume of 1-undecanol was increased from 30 to 70 l. However, the floated phase volume increased from 26 to 60 l, therefore decreasing the concentration of analytes in extraction solvent due to the dilution effect. As a result, the extraction efficiency decreased. A volume of less than 30 l of 1-undecanol resulted in a sediment volume less 20 l which was insufficient for determination by the HPLC system with a 20 l injection loop. Thus, in order to have a high enrichment factor and good repeatability, 30 l of
1-undecanol was selected as the optimum volume of the extracting solvent.