the experimental sensitivities
for each element were estimated. The results obtained are expressed
as the mean values and associated standard deviations of six
independent measurements using increasing standard volumes of
1 mL (from 1 mL to 6 mL), and they are displayed in Fig. 3. As shown,
no significant variations in terms of sensitivitywere found when using
different initial standard solution volumes to perform the WDXRF
analysis. This fact proves that the sample preparation based on the
dried residue method is repeatable and that the use of an internal
standard to check for any inhomogeneities in the prepared samples
was not required.