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13
and exposure of the analytes, such as endrin, to the metal surfaces outside
the glass liner. During injection, the vapor cloud expands outside the glass
liner, exposing reactive analytes tometal surfaces. Endrin and 4,4'-DDT are
usedas indicator compounds for active sites. Themost commonactivearea in
the injectionport is thebottomof the injectionport, below the liner. The vapor
cloud expands past the column and comes in contact with the metal disk
(inlet seal) below the liner. These inlet seals should be cleaned or replaced
during routinemaintenance. Theuse of a gold or Silcosteel
®
-treated inlet seal
will provide greater inertness.
Resolution Discussion
Formany years, environmental laboratorieshave struggledwith various chlo-
rinated pesticide analytical methods. Not only do the labs keep track of reso-
lution requirements and breakdown performance criteria, but they also ana-
lyzeextracts thatusuallycontainhigh-boilingcontaminants.While thesecon-
taminantsdon’t alwaysappear in theGC/ECDchromatogram, theycancause
shifts in retention time, elevatedbaselines, and target compoundbreakdown.
Many laboratorieshaveused cyanopropyl capillary column stationary phases
(1701 columns), whichmay provide the best resolution between target com-
pounds, but have several limitations:
1.1701-typecolumnsareprone toon-columnbreakdownofDDTandmeth-
oxychlor as a result of degradation of the stationary phase. While each
column can be tested for this before leaving the manufacturer, it is no
guarantee that this problem will not arise after the column has been
subjected to sample analyses. The problem seems to be related to the
basicnatureof the cyanogroup, anddoesnot appear tobe easily solved.
2. 1701-type columns have relatively low maximum operating tempera-
tures, which prohibit final oven temperature ramps high enough to re-
move the higher-boiling oils commonly found in pesticide and PCB ex-
tracts. This procedure, commonly referred to as baking out, is used by
many laboratories to eliminate or reduce the levels of heavier hydrocar-
bons at the end of each analysis, providing that the columns can be
heated to higher levels than those used in the analysis itself.
Several phenyl/methyl phases have also been used for this analysis, includ-
ing a 5% phenyl/35% phenyl/50% phenyl phase.While each of these phases
has a highermaximum temperature and is less reactive, as compared to the
cyanopropyl phases, they all have target compounds that coelute to some
extent. The specific compounds that coelute vary based on the percent of
phenyl composition, but each columnhas at least one coelution. This results
in additional work for the laboratory, and in some cases, requires that both
compounds be reported, even though only onemay be present.
While using two phenyl-phase columns in a dual-column system allows bak-
ing-out of the system between analyses, the phenyl-phase columns aremore
prone to coelution of the chlorinated pesticides than the cyanopropyl-phase
columns. This has kept the cyanopropyl-phase columns in demand for pesti-
cide analysis, despite their limitations—until now.
The development of the Rtx
®
-CLPesticides and the Rtx
®
-CLPesticides2 col-
umns has simplified the choice. These columns are capable of baseline reso-
lution of the 22 common chlorinated pesticides as listed inUS EPAMethods
8081, CLP, and 608. Each column is available in 0.25mm, 0.32mm, and
0.53mm IDs, and has been optimized for ECD analysis. Both feature almost
zero bleed after conditioning. In addition to their separating ability, the Rtx
®
-
CLPesticides columns can be heated to temperatures previously only toler-
ated by phenyl-phase columns. The maximum temperature of the Rtx
®
-
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