This view of a signal is caused by an increase in the concentration of
mercury in the vaporwhen the samplewas heated, but then Hg amount
drops down and the signal decreases. As seen in Fig. 1 for a sample of
SiO2, where only the ionic species of Hg are presented, the peak has a
unimodal shape. The same reproducible results were observed for the
majority of ND samples but several samples like UDD-Alit or UDDNanoGroup
had bimodal peak shapes. This did not affect the Hg determination
as the total area is used for calculations. The peaks for some
of the test samples are shown in Fig. 3.