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By Chris Rattray
• Accurately quantify active semivolatiles down to 0.5 ng on-column using GC-MS.
• Extended linear range allows lower detection limits to be met, while minimizing dilution and
reanalysis of high concentrations samples.
• Maintain critical separations with a fast 17 min analysis time.
Customers and regulatory agencies are increasingly requiring lower
GC-MS detection limits for semivolatile organic pollutants. Extending
the linear calibration range down below typical levels is the best way
to accomplish this, while still minimizing the dilution and reanalysis of
heavily contaminated samples. Analyzing semivolatiles, particularly
active compounds, at sub nanogram on-column levels requires a highly
inert GC system. First, an inert sample pathway results in tall, narrow
peaks that improve detectability by maximizing signal-to-noise ratios.
Second, the lack of reactivity reduces adsorptive losses of active ana-
lytes, which minimizes variation of the relative response factor (RRF) at
low levels. As shown in the data reported here, lower detection limits
for active semivolatile compounds can be achieved when the entire
gas chromatographic system (liner, seal, and column) is highly inert.
Inert System Improves Response at Trace Levels
For this work, 143 semivolatiles listed in the extended EPA Method
8270, including Appendix IX compounds, were calibrated across a
concentration range of 0.5-120 ng/µL. The 17-minute analysis shown
in Figure 1 used an Agilent GC-MS (7890-5975C) equipped with a
Siltek® deactivated EZ Twist Top® split/splitless inlet (cat.# 22178). A
Sky™ inlet liner with wool (cat.# 23303), a Flip Seal™ inlet seal (cat.#
23411), and an Rxi®-5Sil MS column (30 m x 0.25 mm ID x 0.25 µm,
cat.# 13623) were also used to ensure an inert sample path. The
selectivity of the Rxi®-5Sil MS column separated critical isobaric pairs,
such as the benzo[b]- and benzo[k]fluoranthenes, as well as aniline
and bis(2-chloroethyl)ether.
The inertness of this system produces good peak shapes and respons-
es even at 0.5 ng on-column for active compounds. This is particularly
evident in a comparison of the responses of 2,4-dinitrophenol and
4-nitrophenol at different concentrations (Figure 2). While the relative
decrease in 2,4-dinitrophenol response at lower concentration indi-
cates some adsorptive loss is occurring, the peak response still exceeds
method criteria by a factor of 5 (Table I).
Quantify Semivolatiles Down to 0.5 ng On-Column by GC-MS
Using an Inert Inlet Systemand an Rxi®-5Sil MS Column to Extend the Calibration Range
Lower Detection Limits for Active Compounds
Chloro- and nitro- anilines and phenols are good indicators of system
performance. They are highly reactive and the minimum performance
criteria in the method are difficult to meet with a poorly deactivated
column and liner. Tables I and II show the performance of these trou-
RRF
(0 .5 ng) Minimum RF Average RRF(0.5–120ng/µL)
RRF
RSD Linear R
2
2-Nitrophenol 0.710 0.100 0.770 6.9% 0.9999
2-Nitroaniline 0.204 0.010 0.226 5.4% 0.9999
3-Nitroaniline 0.218 0.010 0.226 3.5% 0.9997
2,4-Dinitrophenol 0.055 0.010 0.176 42% 0.9992
4-Nitrophenol 0.234 0.010 0.254 8.0% 0.9914
4-Nitroaniline 0.433 0.010 0.424 3.9% 0.9995
4,6-Dinitro-2-methylphenol 0.119 0.010 0.237 28% 0.9999
Table I: Nitroanilines and nitrophenols performance summary.
RRF
(0 .5 ng)
Minimum
RRF
Average RRF
(0.5–120ng/µL)
RRF
RSD Linear R
2
2-Chlorophenol 1.606 0.800 1.512 3.2% 0.9998
2,4-Dichlorophenol 1.157 0.200 1.155 2.9% 0.9995
4-Chloroaniline 0.468 0.010 0.456 6.3% 0.9971
4-Chloro-3-methylphenol 0.284 0.200 0.289 2.1% 0.9998
2,4,6-Trichlorophenol 0.400 0.200 0.415 4.4% 0.9999
2,4,5-Trichlorophenol 0.435 0.200 0.442 2.9% 0.9997
2,3,5,6-Tetrachlorophenol 0.327 0.010 0.377 9.3% 0.9987
2,3,4,6-Tetrachlorophenol 0.357 N/A 0.372 3.9% 0.9984
Pentachlorophenol 0.238 0.050 0.311 14% 0.9999
Table II: Chloroaniline and chlorophenols performance summary.
Semivolatiles