Gschwend%20thesis.pdf

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Briefly, the method involves bubbling a warmed seawater sample
with helium and passing the effluent gas stream through a trap loaded
with a solid adsorbent, Tenax. The volatiles, which are concentrated
on this trap, are transferred by thermal desorption within a gas
chromatograph injection port into a cryogenic loop which was made by
reshaping the front end of the glass capillary gas chromatography
column. After this transfer, the loop is warmed and chromatography
is performed.
The method determined those compounds of sufficient volatility
and low solubility to be stripped (hence the term "stripability")
and not interfered with by the variable contamination (presumably
o
atmospheriq by compounds boiling below 100 C. The lower limit of
detection for nonpolar compounds was about i ng/kg seawater.
Precision, as determined by the recovery of l-chloro-n-decane added
to the seawater at 10 ng/kg, was + 20%. Compound recoveries varied,
but were better than 80% for nonpolar volatile compounds, about 50%
for slightly polar compounds such as alkylated benzenes, and less
than 20% for more polar compounds such as the aldehydes.
The Peru seawater samples were analyzed using the "Grob" method
(Grob, 1973; Grob and Zürcher, 1976; Schwarzenbach et al., 1978;
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Appendix I). Just before analysis, 200 m1 of water was poured off
at a nearby beach to provide a clean-air headspace. At the lab,
samples were stripped for 2 hours at 35 C using the recycled head-
space air. Volatile compounds were collected on a charcoal trap
placed in the recycling vapor path. After the water was stripped,
the trap was extracted with l5 l11 CS2. GC and GCMS analyses were
performed on aliquots of this extract.