For preparation of the standard solutions, 1000 μg of pureHMPHA powder was diluted in 1 mL of HPLC mobilephase solvent to prepare the stock solution of 1000 μg/mL.Different standard solutions at concentrations of 4.5, 6, 8,10, 12.5, and 15 μg/mL were prepared by serially dilutingthe stock solution.