Two experimental procedures were used for the gas effect
studies. The first procedure discussed above is relatively long,
and the study of all gas pairs takes several days to complete. To
determine the effect of drift in the ICP and laser power on these
measurements, a second procedure was used to complement the
data from the first experimental procedure. For the second
procedure, approximately six laser power densities were used for
each gas pair combination. The ICP was kept operative when
the gases were changed. There was only one sample change,
and the measurements were carried out in a relatively short period
of time (6 h); changes in instrumental conditions were determined
to be minimal compared to the first experimental procedure.
By using the second procedure, direct comparison of ICP
emission intensity was possible. In addition, the trends in data
from both experimental procedures were found to agree.