Gschwend%20thesis.pdf

Grob Methodology
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The methods of Grob (1973), Grob and ZUrcher (1976) and Schwarzenbach
et al. (1978) were used to analyze seawater samples from the Peru upwelling
region. Briefly ~ this involved stripping a 2-1i ter seawater sample in a
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recirculating fashion for 2 hours at 35 C and 1.5 literslminute flow.
Purged volatiles were trapped on a charcoal trap consisting of i mg charcoal
sandwiched between 2 stainless steel screens. After stripping, 20 ng l-
chloro-n-oc tane in 2 ~ i CS 2. was added to the trap and then the trap was
extracted w.ith is ~l CSZ' Further analysis was by GC or GCMS,
Method Tests
In order to investigate the effects of filtering and poisoning on the
Peru upwelling region samples~ 6 samples were drawn in replicate and
subj ected to different combinations of these treatments (Table 1-3). The
two deepest samples (6/1000 m and 5/900 m) suggest that the treatments do
not add significant volatile compound concentrations (i.e., less than about
2 ng/kg).
Shallow control samples suggest that filtering may remove some volatiles.
This was particularly evident for the aldehydes in the 5~meter samples.
Filtered samples contained 40 to 70% lower aldehyde concentrations than did
unfiltered ones. Filtering experiments on coastal seawater samples conducted
before the cruise, indicated that only high~boiling nonpolar compounds such
as pentadecane and naphthalene were removed by filtration (about 50% removal).
Therefore, some volatiles may be associated with particles in seawater,
and caution must be exercised in comparing filtered and nonfil tered samples.
In an. experiment to assess the effects of seawater storage on the
volatiles, 30 liters of coastal seawater were collected in a Niskin sampler,
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