environmental
Applications
note
Restek Corporation • (800) 356-1688 • (814) 353-1300 •
#59196A
Analysisof PolycyclicAromaticHydrocarbons (PAHs) UsingRtx
®
-5SilMSand
Rtx
®
-CLPesticides2CapillaryColumns
environmental
Analysis of polycyclic aromatic hydrocarbons (PAHs) is a
very commonmethod in environmental laboratories. US
Environmental ProtectionAgency (EPA)Method 8100 requires
gas chromatograph/flame ionization detection (GC/FID) to
quantitate PAHs found in extracts fromsoil, water, or biologi-
cal samples. Thismethod requires the use of a dual-column
system, becausemost samples often contain hydrocarbon inter-
ferences. Confirmational analysis increases the confidence of
proper identification and quantitation of the PAHs. Good reso-
lution is necessary for proper quantitation; themost difficult
compound pairs to resolve are benzo(b)/benzo(k)fluoranthene
and indeno(1,2,3-cd)pyrene/dibenzo(a,h)anthracene. Short anal-
ysis time is another key consideration formost laboratories. By
decreasing analysis time, sample throughput is increased and
the lab benefits froma cost savings.
PrimaryAnalysis
For this analysis, the primary analytical stationary phase is a
5%diphenyl/95%dimethyl-polysiloxane polymer. TheRestek
Rtx
®
-5SilMS column is an equivalent phase and is recom-
mended for this analysis (Fig. 1).While selectivity is similar to
5%diphenyl/95%dimethyl-polysiloxane columns, the propri-
etary silarylene stationary phase of theRtx
®
-5SilMS column is
designed to produce very lowbleed.
Confirmational Analysis
Confirmational analysis is a technique that requires two analyti-
cal columns of different selectivities, resulting in different reten-
tion times of target or interfering compounds. These differences
can improve quantitative and qualitative reliability through peak
verification. The confirmational column recommended by
Restek for this analysis is theRtx
®
-CLPesticides2 column (Fig.
2). Quantitative reliability for this analysis ismaintained
because the stationary phases differ in selectivity, resulting in
retention time shifts of both PAHs and interference compounds.
Resolution of PAHs
Resolution between benzo(b)fluoranthene and benzo(k)fluoran-
thene and indeno(1,2,3,-cd)pyrene and dibenzo(a,h)anthracene
is essential for quantitationwhen using an FID. To achieve
excellent resolution of these peak pairs, the carrier gas, column
flow rate, and temperature programmust all be optimized.And,
to achieve even better quantitative reliability, it is recommended
to clean sample extracts followingEPAMethod 3630 (silica
gel) prior to analysis.
OptimizingCarrier Gas Flows
The resolution of PAHs can be increased and the overall analy-
sis time reduced by using hydrogen carrier gas at high flow
rates. For this application hydrogen is a better choice than heli-
umbecause it ismore efficient at higher flow rates.And, if used
in the constant flowmode, the best separation and fastest analy-
sis time can be achieved. (Constant pressuremode is not recom-
mended because the flow ratewill decrease as the oven temper-
ature is increased. This could result in a loss of resolution for
the later eluting PAHs and a longer analysis time.)
The optimumcarrier gas flow rate for the 30m, 0.25mmID,
0.25µmRtx
®
-5SilMS column is less than 1mL/min. However,
by increasing the flow rate to 4mL/min. for the analysis of
PAHs, the separation of the isomer pairs is increased and the
analysis time is reduced to less than 17minutes (Figure 1). The
Rtx
®
-CLPesticides2 confirmation column can separate these
compounds under identical conditions (Figure 2).Again, the
faster flow rate (4mL/min.) improves separation and reduces
analysis time to less than 18minutes.
Figure 1–TheRtx
®
-5Sil MS column exhibits
excellent resolution of polycyclic aromatic
hydrocarbons including benzo(b)/benzo(k)fluoran-
thene in less than 16minutes.
Rtx
®
-5SilMS 30m, 0.25mm ID, 0.25µm (cat.# 12723)
Sample:
50µg/mL610 PAHMix standard (cat.# 31011)
in carbon disulfide
Inj.:
1.0µLsplitless (hold 2min.),
2mm splitlessw/ wool inlet liner (cat.# 20829)
Inj. temp.:
330°C
Carrier gas: hydrogen, 4mL/min constant flow
Oven temp.: 40°C (hold 2min.) to 250°C@25°C/min. to 265°C
@5°C/min. to 300°C (hold 4min.)@25°C/min.
Det.:
FID@350°C
5. phenanthrene
6. anthracene
7. fluoranthene
8. pyrene
GC_EV00595
1. naphthalene
2. acenaphthylene
3. acenaphthene
4. fluorene
9. benzo(a)anthracene
10. chrysene
11. benzo(b)fluoranthene
12. benzo(k)fluoranthene
13. benzo(a)pyrene
14. indeno(1,2,3-cd)pyrene
15. dibenzo(a,h)anthracene
16. benzo(ghi)perylene
