Gschwend%20thesis.pdf

-ZIO-
ionization spectra were acquired using CH4 as the reactant gas at 950 ~
o
pressure, with the ionization chamber at about 180 C and 130 eV ionization
potentiaL.
Evalua tion of the Method
Blanks were determined throughout the cruises. Precleaned Tenax
traps were placed on the helium~flushed empty stripper. Helium purging
was begun, as if the seawater sample were in place, and continued for
5 minutes. At the end of this time the trap was removed -to a screw-
cap vial and stored in the freezer along with other sample traps until
GC analysis. Typical gas chromatograms for blanks (no standards added)
and open ocean seawater samples are shown in figure i-Z. The blank
chromatogram was very similar to that shown previously by May et al.
(1975) . Contamination peaks were present in the "solvent regionll
(pentan~ acetone, methylene chloride) and for this reason, and because
the resolution in this region of the chromatogram was poor, this part
of the gas chromatograms was subsequently ignored.
Peaks were also
present near the high-boiling end of the chromatogram, but these elute
beyond the volatile compounds Qoncentrated by stripping.
A large and variable blank was found for the western Equatorial
Atlantic samples. Identification
of the compounds found in this contam-
ination showed the presence of several unusual compounds which were
stored in the same refrigerator as the Tenax traps. Traps stored in
more than one refrigerator before GC analysis showed contamination from
compounds unique to each refrigerator. Thus f Tenax trap storage in the
screw-cap vials was not always adequate for the prevention of large
blanks.