Gschwend%20thesis.pdf

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purchased them. Tenax may be more inert than charcoal in terms of degrading
the volatiles. Thermal desorption of Tenax is efficient. On the other
hand, charcoal traps desorb only about 35% of naphthalene and about 60% of
l-octanol. The Tenax method may allow for greater sensitivity as the entire
sample is introduced into the GC? while the Grob technique limits this to
about 10-20% of the sample. If good storage methods are devised, Tenax
may allow the analysis of very low-boiling compounds. This is impossible
with the Grob method due to solvent interference.
On the other hand? the Grob procedures offer certain advantages.
Relatively involatile compounds are recovered more efficiently.. This,
in turn, facilitates greater reproducibility (1 sigma about 10% compared to
20% observed for Tenax). The gas recirculation method tends to maintain
the chemical character of the seawater sample (e.g., oxygen content). This
may help preserve the organisms in unfiltered samples. Helium? on the
other hand, would strip oxygen~ which may be useful for inhibiting oxidation
reactions during stripping. Methods for the introduction of internal stan-
dards are easier for Grob techniques and enable monitoring of two separate
steps in the procedure. Probably the most important advantage of the Grob
system is that multiple GC or GCMS analyses of the volatile concentrate
are possible. This allows analysis on more than one type of column.
Stream splitting of the purging gas onto several Tenax traps could poten-
tially provide similar multiple-analysis capability, but this has proved to
be an irreproducible procedure.
Both methods allow for good sample storage. In this work, Tenax
traps have retained their volatiles for many months; the problem we have
experienced with these traps is that, unless they are adequately isolated,
they will acquire high contamination levels, Grobmicrovialscan retain