By using the previously selected
variables, the concentration of nanoparticles was studied
from 1.25 to 8.0 lmol L1. It was observed that the DF increased
initially, with increasing nanoparticles concentration, reaching
the maximum value for 2.3 lmol L1 and decreasing for higher values
(Fig. 3). This could be explained by the occurrence of inner filter
effects due to re-absorption of emitted radiation [31]. A
concentration of 2.3 lmol L1 was selected for the determination