environmental
Applications
note
Restek Corporation • (800)356-1688 • (814)353-1300 •
#59131
environmental
PID
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TheRtx
®
-5Sil MSColumnProvides theBest Resolution for GasolineRange
Organic (GRO) Compounds Listed inAlaskaMethodAK101AA
Figure1
TheRtx
®
-5SilMS column resolves the alkyl benzenes and
all the branched aromatic compounds listed in theAlaska
GROMethodAK101AA providingmore accurate
identification and quantitation.
TheAlaskaDepartment ofEnvironmentalConservation (ADEC)
developed anew technique for thegas chromatographic (GC)
analysis of gasoline rangeorganic (GRO) compounds in soil,
water, andwastewater—MethodAK101AA. Thismethod
quantitates aromatic and aliphatic compounds fromC6 (hexane)
toC10 (decane), and is capable of a higher level of accuracyover
existingGROmethods. Restek’sRtx
®
-5SilMS column is ideal
for the analysis ofGRO compounds, and specificallymeets the
requirements ofMethodAK101AA.
ThekeydifferencebetweenAK101AA andotherGROmethods
that usephotoionizationdetection/flame ionizationdetection
(PID/FID) for differentiationof aliphatic and aromatic com-
pounds, is thatAK101AAuses theC9 alkyl benzenes (e.g.,
methyl ethylbenzenes) as target compounds in the calibration
mixture.Using specific compound identification reduces error
over otherGROmethods that relyonlyonPID ranges for the
determinationof aromatic compounds.This canhelpdetermine
thedifferencebetweenhighlydegradedgasoline and light
components of diesel fuels, such as kerosene and arctic fuel.
MethodAK101AAprevents a highbias in reportingof aromatic
compoundswhen they are in the presence of alkenes and
alkynes.These are straight-chainunsaturated compounds that
cangive a false positive on thePID. Because all gasoline
compounds respondon theFID, the total quantitationof gasoline
is achievedwith this detector, and the identificationof single
compounds areperformedwith themore selectivePIDdetector.
MethodAK101AA alsodisregards analytes elutingbeforeC6
because thesepentanes andoxygenates have similar retention
and arepoorly resolved.
1. hexane
2. benzene
3.
α
,
α
,
α
-trifluorotoluene (ss)
4. toluene
5. ethylbenzene
6.
m
-xylene
7.
p
-xylene
8.
o
-xylene
9. isopropylbenzene
40m, 0.45mm ID, 1.50µmRtx
®
-5Sil MS (cat.# 12798). Injection of
4-bromofluorobenzene (cat.# 30026);
α
,
α
,
α
-trifluorotoluene
(cat.# 30048), decane, hexane, andAlaska aliphatic/aromatic GROmix
(cat.# 30461).
GC:
Finnigan 9001;
Column flow:
9mL/min.;
Concen-
trator:
Tekmar LSC-3000 Purge&Trap, BTEX trap;
Interface:
direct
with Siltek
™
transfer line;
Oven temp.:
40°C (hold 2min.) to 85°C@
4°C/min. (hold 1min.) to 225°C@ 40°C/min. (hold 2min.);
Det.:
FID (280°C)/PID (200°C);
Make-up flow rate:
15mL/min.
10. 4-bromo-fluorobenzene (ss)
11.
n
-propylbenzene
12. 1-ethyl-3-methylbenzene
13. 1-ethyl-4-methylbenzene
14. 1,3,5-trimethylbenzene
15. 1-ethyl-2-methylbenzene
16. 1,2,4-trimethylbenzene
17. decane
18. 1,2,3-trimethylbenzene
min. 2
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PeakList andConditions for Figure 1
FID
min. 2
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