Intra- and interday variability were utilized to evaluate precision. The mixed standard solution at low, medium, and high concentrations in one day (n = 3) and on three consecutive days was analyzed, respectively. The results (Table 4) indicated that the mean intraday R. S. D. values of compounds 4 and 7 were less than 3.97% and the mean interday R. S. D. values of compounds 4 and 7 were less than 6.99%.