Ca determination was performed to count the reference values
for all samples. For this task, the 0.1 g sample was placed in a Teflon
microwave vial. Next, 1.0 mL of nitric acid 14 mol L1
, 1.0 mL of
hydrogen peroxide 30% (v/v) and 1.0 mL of ultra pure water were
added to the sample.