The stock standard solution of 2-naphthol and 4-nitrophenol
were prepared in methanol of HPLC grade with concentration of
0.35 and 0.10 mgmL1, respectively,and stored at 4 1C before use.
Then the working solutions were prepared freshly by diluting the
stock solution with ultrapure water and used immediately for the
optimization of IL/ILDLLME procedure and the method validation.
Calibration standard solutions containing 2-nathphol and 4-nitrophenol were prepared by ultrapure water over the concentration
rangeof28–336 and24–384 μg L1.