The need of sample pre-treatment was also evaluated, comparing
the microwave-assisted acid digestion procedure described in
Section 2.3 with the results obtained by direct sample analysis.
There were no significant differences in the results obtained with
direct analysis and microwave-assisted digestion; the results were
identical, within 95% of confidence. Hence, direct analysis was used
for the following experiments, resulting in lower reagent consumption,
lower risk of contamination and shorter total analysis time.