RestekCorporation • (800)356-1688 •
PeakList andConditions for Figure 2
Figure2
Comparing patterns and elution can help determine un-
weathered gasoline, kerosene, and diesel fuel.
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).
Injections of gasoline, kerosene, and diesel.
Column flow:
9mL/min.;
Concentrator:
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.:
GC/MSTIC.
TheRtx
®
-5SilMS column is capable of resolving all 13 aromatic
compounds listed in themethod.Columns commonlyused for
GRO analysis, such as theRtx
®
-5 andRtx
®
-502.2 columns,
cannot adequately resolve theC9 alkyl benzenes.TheRtx
®
-5Sil
MSphasedesign, columndimensions, and suggestedGC
conditions areoptimized toprovide thebest possible resolution
of the alkyl benzenes and all the branched aromatics listed in the
Alaskamethod (Figure 1).Additionally, the 40m length and a
0.45mm internal diameter (ID) results in fasterGC run-times,
reduced cost, and lower columnbleed. Bleed levels are excep-
tionally low even at temperatures up to300°C.
TheFID chromatogram inFigure 1 shows the elutionof the
AK101AA target compoundswith the additionof two surrogates
and twowindowmarkers—
α
,
α
,
α
-trifluorotolueneand
4-bromofluorobenzene, andC6 andC10 , respectively. Twoof
theeight aromaticC9compounds—1,2,4-trimethylbenzeneand
1,2,3-trimethylbenzene—have longer retention timeson the
Rtx
®
-5SilMS column than theC10marker, thus these two
analytes elute after decane.All theC9 aromatic compounds are
included for analyte quantitationon thePID,whereas theFID
uses the total gasoline range quantitation,which endswithC10.
Unweatheredgasoline, kerosene, anddiesel fuelwere analyzed
under the same conditions to illustrate the differences in their
patterns and elution (Figure2). These threedifferent fractions of
petroleumwere analyzedusingGC/mass spectrometry (MS),
with theC9 aromatic compounds labeled. Thedistribution and
concentrationof theC9 aromatics is different dependingon the
following: degreeofweathering, typeof fuel, and sourceof the
petroleum. It is important to runbothweathered andunweath-
ered fuels usingPID/FID andyour conditions to assist in
determining the types of petroleum anddegrees ofweathering.
Figure3 shows examples of theC9 aromatic compounds found
ingasoline andkerosene, analyzedusingGC/MS in selected ion
monitoring (SIM)mode and scanning forM/Z120.These alkyl-
benzenes are theonly compounds that share ions 105 and120 in
this regionof the chromatogram. Concentrations ofC9 com-
pounds found inkerosene andgasolinediffer by anorder of
magnitude; therefore, the standardsweremade in twodifferent
concentrations toproduce a similar signal intensityon theMS
system.The areaof eachC9 aromatichydrocarbonwas com-
pared relative to the total area of all eight of these compounds in
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
Unweathered gasoline
min. 2
4
6
8 10 12 14 16
11
9
12
13 15
14
16
18
18 20 22
Unweatheredkerosene
min. 2
4
6
8 10 12 14 16 18 20 22
16
13
14 12
11 9
18
15
Unweathereddiesel fuel
16 13
14 12
11 9
18
15
min. 2
4
6
8 10 12 14 16 18 20 22
