Sampling and Laboratory Analysis for Solvent Stabilizers - Environmental Investigation and Remediation - page 218

4.5.5 E NVIRONMENTAL P ROTECTION A GENCY M ETHOD 8270C—E XTRACTED S EMIVOLATILE
O RGANIC C OMPOUNDS BY G AS C HROMATOGRAPHY -M ASS S PECTROSCOPY
EPA Method 8270C is a GC-MS method designed to analyze for semivolatile organic compounds on
extracted samples. This method targets compounds that are soluble in methylene chloride and capable
of being eluted as sharp peaks from a gas chromatographic fused-silica capillary column coated with
a slightly polar grade of silicone (USEPA, 1996c). Sample-preparation methods for EPA Method
8270C include LLE. EPA Method 8270C uses a single-column coni guration, 30-m-long silicone-
coated fused-silica capillary column (J&W Scientii c DB-5 or equivalent) with a 0.25 or 0.32 mm
internal diameter and a 1 m i lm thickness (USEPA, 1996c). 1,4-Dioxane is not a listed analyte in

EPA Method 8270C; however, the method can be adapted for compound-specii c analysis with isotope
dilution to quantify 1,4-dioxane with reporting limits as low as 0.5

μ

g/L (Weck Laboratories, 2006).
In analyses using extractable sample-preparation methods, 1,4-dioxane elutes immediately after
the solvent front, * which reduces interference from other compounds. In isotope dilution, samples
are spiked with 1,4-dioxane-d 8 and then subjected to routine sample extraction procedures. For
improved resolution, the sample extract can be reanalyzed with the mass spectrometer in SIM mode.
Isotope dilution in MS analysis involves comparing the mass differences between 1,4-dioxane and
its deuterated analog, 1,4-dioxane-d 8 . 1,4-Dioxane-d 8 is the ideal internal standard for 1,4-dioxane
because it has similar chemical properties as 1,4-dioxane, but its mass spectra are distinctly different
(Linton and Alonso, 2006). Samples can be analyzed for 1,4-dioxane by using the full-scan method
with other semivolatile analytes, but with higher detection limits (Strout et al., 2004b).
Isotope dilution improves precision and accuracy by reducing the problems with calibration and
sample-preparation matrix effects. Some analytes are not easily recovered during chromatography or
sample extraction. Calibration problems and matrix effects are usually compensated for in part by
using internal standards and surrogate analytes. In 1,4-dioxane-d 8 , hydrogen atoms on the 1,4-diox-
ane molecule are replaced with deuterium atoms. † The 1,4-dioxane-d 8 is available as “99 atom%
deuterium,” meaning that 99% of the sites on the 1,4-dioxane ether ring normally occupied by 1 H are
occupied by deuterium in the standard. In GC analyses, the error from methods used to inject the
sample can be approximately 5%. By adding an internal standard, the error can be reduced by half to
approximately 2-3%. With isotope dilution, the error should be half of that again, approximately 1%
(Lindsay, 2000).
To achieve low-level reporting limits by EPA Method 8270C, commercial laboratories have
adjusted the method by adding a salting-out step that uses large-volume injection of sodium chloride
or sodium sulfate and by running the mass spectrometer in single ion mode. For example, a method
use d by Colu mbia A na ly t ica l Ser v ices i nvolves sepa r ator y f u n nel ext r a ct ion usi ng d ich loromet ha ne
on a 100 mL sample spiked with 1,4-dioxane-d 8 and prepared with NaCl. The extract is dried and
reduced to a i nal volume of 5 mL. A large-volume injector is used to introduce the sample to the
GC-MS, which is run in SIM mode. Columbia Analytical Services reports that a method reporting
limit of 0.1

μ

μ g/L is routinely achievable through the use of this approach (Grindstaff, 2004).

4.5.6 E NVIRONMENTAL P ROTECTION A GENCY M ETHOD 1624 —I SOTOPE -D ILUTION
G AS C HROMATOGRAPHY -M ASS S PECTROSCOPY
EPA Method 1624 is a modii cation of Method 8270C. Method 1624 also adds 1,4-dioxane-d 8 to the
sample as an internal standard prior to extraction. Losses of the target analyte that may occur during the

* The solvent front is the chromatographic peak corresponding to the carrier solvent, usually dichloromethane, used to
extract the analyte from the sample.
† Deuterium, written as 2 H or D, is the naturally occurring stable isotope of hydrogen. It has one extra neutron and is there-
fore heavier than hydrogen. Deuterium has the same chemical properties as hydrogen. A “deuterated” standard is pre-
pared so that molecular sites normally occupied by 1 H are replaced with deuterium.