The precision was evaluated over the sample
preparation step of the proposed methodology. The precision was
determined at each concentration level, and did not exceed 15% of
the percent relative standard deviation (%RSD) except for the LOQ,
which it did not exceed 20% of the RSD [31,32]. The resulting RSDs
values in the LOQ level ranged from 0.10 to 19%, and 1.0e15% for the
remaining concentration level.