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2007 vol. 3
Sample Preparation
Superior Fractionation of Extractable PetroleumHydrocarbons
Get More Accurate Results Using Restek SPE Tubes
By Lydia Nolan, Innovations Chemist
• Easier quantitation; lower background & less interference.
• Reliable, reproducible results.
• Unique packaging designed for convenience and storage stability.
There is an increasing public awareness of the
threat to public health from leaking underground
storage tanks. Both federal and state agencies have
developed methods to address the testing of
potential problem sites. The Massachusetts
Department of Environmental Protection’s “Method
for the Determination of Extractable Petroleum
Hydrocarbons (EPH)” has recently been updated
and is based on solvent extraction of water and
soil/sediment matrices, followed by silica gel SPE
fractionation of aliphatics and aromatics from C9
through C36 hydrocarbon ranges.
The quality and conformation of the silica SPE
clean-up column is essential to acceptable frac-
tionation and recovery results. Commercial silica
SPE products streamline this process, but it is
important to understand the quality and perform-
ance differences among the available products, and
the impact they have on your results. The activity
level and capacity of the silica, the compression of
the bed, and the quality of the constituents and
packaging are all critical to getting accurate and
reliable results. The data in Table I show how even
very minor amounts of excess moisture (known
amounts added for experimental purposes during
the first conditioning step) or long-term storage
without desiccation can produce early break-
through of the sensitive analytes from the aromatic
fraction into the aliphatic fraction.
To ensure maximum shelf-life and minimum envi-
ronmental exposure after opening these cartridges,
Restek packages them into 5 smaller packs of 4 SPE
tubes each—the fewest cartridges per pack avail-
able. We also provide an additional outer, reseal-
able barrier bag, making successful short- and
long-term product storage easier for the user.
Activity level of the silica and consistency of the
cartridge packing are essential for reliable fraction-
ation recovery and reproducibility. The recovery
and reproducibility of results for the fractionation
surrogates (2-fluorobiphenyl, 2-bromonaphtha-
lene and naphthalene) are critical to determining if
breakthrough is occurring. Again, in comparing
several commercial sources, using optimized con-
ditions for each vendor, results show that the
Restek Massachusetts EPH cartridges are capable
of quantitative (greater than 97%) and reliable
(RSDs less than 7.3) recoveries for these critical
markers (Table II).
Figure 1
Restek Massachusetts EPH SPE tubes show the lowest
overall level of background response.
* Total area counts exclude response for solvent front and surrogate peaks
1.
o
-terphenyl (surrogate) 10ng on-column
2. 1-chlorooctadecane (surrogate) 10ng on-column
All cartridges were extracted with 15mL hexane, without prior conditioning. Extract blanks were then
spiked with the 50µL of MA EPH Surrogate Spike mix, cat#31479 (diluted to 400µg/mL with hexane), and
dried down to 1mL with gentle nitrogen purge.
GC_EV00929
GC_EV00928
GC_EV00927
GC_EV00926
Column: Rtx
®
-5, 30m, 0.32mm ID, 0.25µm (cat.# 10224)
Sample: Massachusetts EPH Surrogate Spike Mix (4000µg/mL each component) diluted to 400µg/mL in hexane.
Spiking standard: 50µL Inj.: 0.5µL, splitless (hold 0.5 min.), PSS split/splitless inlet liner (cat.#21717)
Inj. temp.: 280°C; Carrier gas: helium, constant velocity; Pressure pulse program: 50cm/sec @ -0.71 min.,
split ratio = 0 @ -0.70 min., split ratio = 20:1 @ 0.75 min., 35cm/sec @ 0.8 min.; Linear velocity: 35cm/sec
Oven temp.: 60°C (hold 1 min.) to 310°C @ 8°C/min. (hold 12 min.), Det.: FID @ 330°C
Peak List
1.
o
-terphenyl (surrogate, 10µg/mL)
2. 1-chlorooctadecane (surrogate, 10µg/mL)
Restek
Total Area: 392766
Vendor A
Total Area: 450293
Vendor B
Total Area: 645985
Vendor C
Total Area: 442163
Minimize background
with Restek SPE tubes!