Geology Reference
In-Depth Information
calibrated volumetric (Class A). The extract is spiked with surrogate and brought up to 10mL volume. A small
aliquot is removed to determine the TEM.
Cleanup
P
ure coal and coal-tar samples may not require cleanups due to the relative hydrocarbon purity. If the sample
contains high concentrations of interferences, like polar (NSO-bearing) compounds or elemental sulfur, then one or
more cleanups are recommended. The isolation of geochemical biomarkers is always recommended for coal-tar
samples.
Alumina Solid Phase Cleanup of Polar Organics
Alumina solid phase cleanup is used to remove polar organic compounds from the sample extract. The reference
method is EPA Method 3611B (USEPA, 2008). A chromatography column is fitted with a Teflon stop cock.
A glass wool plug is placed inside the column, on top of the stop cock. The column is packed with a 10 g bed of
alumina (solvent rinsed and oven dried granular aluminum oxide) topped with 1 cm of anhydrous Na
2
SO
4
. The
column is rinsed with three bore volumes of DCM. A suitable volume of extract containing 10mg of TEM is
transferred to the top of the column and drawn into the solid-phase packing by opening the stop cock. The column
is then eluted with 30mL DCM and collected into a concentrator tube. The extract is evaporated with a stream of
high-purity nitrogen gas to less than 1 mL. The extract is quantitatively transferred with rinses to a GC autosampler
vial and brought up to 1mL with DCM.
Copper Solid-Phase Cleanup of Sulfur
Elemental sulfur and sulfide can interfere with the measurement of hydrocarbons. High-sulfur coal and coal-tar
samples collected near sulfur crystals benefit from this cleanup step. The reference method is EPA Method 3660B
(USEPA, 2008) or NOAA Status and Trends Program methods (NOAA, 1998). The granular copper (99% purity)
is activated by suspension in 6N hydrochloric acid. While preventing exposure to air, the copper granules are rinsed
with deionized water and stored in DCM. Approximately 2 g of activated copper powder are placed in a 10 mL
scintillation vial that contains the sample extract. The Teflon-lined cap is closed and the sample is mixed by hand,
vortex, or sonicator. If the copper turns black, the cleanup is repeated with a fresh aliquot of activated copper
powder.
Silica Gel Solid Phase Purification of Aliphatic Hydrocarbons
The presence of PAHs interferes with the detection of selected saturated hydrocarbons and geochemical
biomarkers. The aromatic interferences are removed by fractionation with silica gel. The reference method is
EPA Method 3630C (USEPA, 2008). Silica gel is made from sodium silicate and sulfuric acid (100/200 mesh).
The silica gel is purified by extraction with DCM and oven drying overnight at 130°C. A chromatography
column fitted with a Teflon stop cock and glass wool plug is loaded with a bed of silica gel (5 g) topped with
1 cm of anhydrous Na
2
SO
4
. The column is rinsed with three bore volumes of pentane. A suitable volume of
extract containing 25mg of TEM is solvent exchanged to hexane under a stream of nitrogen. The extract is
transferred to the top of the column and drawn into the solid-phase packing by opening the stop cock. The
column is then eluted with 20 mL pentane and collected into a concentrator tube. The extract is evaporated in a
stream of nitrogen to less than 1mL. The extract is quantitatively transferred with rinses to a GC autosampler vial
and brought up to 1mL with hexane.
