For obtaining optimized volume of acetonitrile, various experiments were used by using different volumes of acetonitrile (100, 200, 300, 400 and 500 l) containing different volumes of 1-undecanol and all experiments were performed in triplicates. Variation of the volume of acetonitrile causes changes in the volume of the floated phase; hence, it is impossible to consider the influence of acetonitrile volume on the extraction efficiency. In order to avoid this and also to achieve a constant volume of the floated phase, the volume of acetonitrile and 1-undecanol were changed simultaneously. According to the results in Fig. 3