environmental
Applications
note
RestekCorporation • (800) 356-1688 • (814)353-1300 •
#59111
environmental
MinimizingBreakdownof ChlorinatedPesticidesUsingSiltek
™
-Deactivated
GCAccessories
Gas chromatographic (GC) analysis of chlorinatedpesticides
presentsuniquechallenges toenvironmental laboratoriesbecause
these compounds often are at trace levels and susceptible to
decomposition. Some analyses, such as theUSEnvironmental
ProtectionAgency (EPA)Methods 8081 and608, have stringent
breakdownand reproducibilitycriteria.Breakdownoccurswhen
a compounddecomposes into related compounds, generally
because a thermal or chemical reactionhas occurred. Two
compoundsnotorious for exhibitingbreakdownareendrin,which
breaks down into endrin aldehyde and endrinketone, andDDT,
whichbreaks down intoDDE andDDD. The sourceof break-
down canbe aged samples and standards, theGC columnor,
most commonly, active sites in theGC injectionport. Routine
maintenanceof the injectionport, preventionof sample flash-
back, and thoroughdeactivationof the inlet liner andGC
columns are essential tominimize compoundbreakdown.
We chose apesticide analysis to compareSiltek
™
-deactivated
products against undeactivatedproducts.Toevaluate inlet liner
effects on endrin andDDTbreakdown, anHP5890GC equipped
with anRtx
®
-CLPesticides2 column and an electron capture
detector (ECD)was used.A50pg/µL standardof tetrachloro-
m
-
xylene, endrin, 4,4'-DDT,methoxychlor, anddecachlorobiphenyl
was injecteddirectlyonto the column andonto several different
liners.The areaof thebreakdownproductswas thenmeasured.
Heliumwas used as the carrier gas and the followingoven
programwas used: 120°C (hold1min.), to300°C at 9°C/min.
(hold10min.).The injectorwas set at 250°C and theECD at
300°C.
Tomeasure the column (i.e., “system”) breakdown, anon-
column injectionwasmade.This eliminated the effects of the
injectionport.Using this technique, endrinbreakdownwas 1%
andDDTbreakdownwas belowdetection limits (Figure1).
Asamplewas then introducedbydirect injection into an
untreatedglassUniliner
®
sleeve. The advantageof using a
Uniliner
®
sleeve
for adirect injection is that theGC column
forms apress-tight sealwith the liner, allowing thevaporized
sample todeposit onto the columnwithminimal injectionport
contact.Deactivation is critical for this techniquebecause a
direct injectionmaximizes contact of the samplevaporwith the
liner. The injection resulted in62% endrinbreakdownwithno
DDTbreakdown (Figure2).
1
2
3
4
5
Figure1
An on-column injection demonstrates system breakdown
of less than 1% for endrin andDDT using a
Siltek
™
-deactivated inlet liner.
0
10
Figure2
A chromatographic system that is inadequately
deactivatedwill cause poor linearity, poor reproducibility,
as demonstrated by 62% endrin breakdown.
30m, 0.53mm ID, 0.42µmRtx
®
-CLPesticides2 (cat.# 11340).
Inj.:
1µL of 50pg/µL standard.
Oven temp.:
120°C (hold 1min.)
to 300°C@ 9°C/min. (hold 10min.);
Inj. temp.:
250°C;
Det.:
ECD, 300°C;
Carrier gas:
helium.
1. 2,4,5,6-tetrachloro-
m
-xylene
2. endrin
3. 4,4'-DDT
4. endrin aldehyde
5. methoxychlor
6. endrinketone
7. decachlorobiphenyl
1
2
3
4
5
7
6
min. 0
10
20
30
20
30
40 min.
30m, 0.53mm ID, 0.42µmRtx
®
-CLPesticides2 (cat.# 11340).
Inj.:
1µLof 50pg/µL standard.
Oven temp.:
40°C (hold 1min.)
to 300°C@ 9°C/min. (hold 10min.);
Inj. temp.:
250°C;
Det.:
ECD, 300°C;
Carrier gas:
helium.
1. 2,4,5,6-tetrachloro-
m
-xylene
2. endrin
3. 4,4'-DDT
4. methoxychlor
5. decachlorobiphenyl
