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Introduction
This technical guide addresses thepreparation andgas chromatographic (GC) analysis of
semivolatileorganic compounds such as those listed inUSEnvironmental ProtectionAgency
(EPA)Methods 8270, 525, and625; andpolycyclic aromatic hydrocarbons (PAHs) such as
those listed inUSEPAMethods 610 and8100. These analyses are some of themost common
tests performedby environmental laboratories, yet there aremany analytical challenges of
which the analyst needs tobe aware. For example, the samples often are highly contaminated
withnon-target compounds (e.g., hydrocarbons) andquality assurance/control (QA/QC) of
themethods is rigorous. There are several procedures and techniques that canbe employed,
however, tomake these analyses simpler toperform. Review this guide to learn these
techniques and to troubleshoot analytical problems associatedwith themethods.
The compounds addressed in this guide are listed inTable I, butmany additional compounds
are also amenable to these semivolatilemethods. Table I includes the compounds cited in the
USEPAMethods, aswell as some other compounds typically analyzed in environmental
samples.
Extraction
The compounds listed inTable Imaybe difficult to extract because they fall intodifferent
chemical classes (i.e., acidic, basic, neutral, halogenated, oxygenated, polar, non-polar, low-
boiling, andhigh-boiling compounds). Therefore, the extractionmethodwill need to solvate a
wide varietyof compounds. It alsomust recover the analytes of interestwhile removing the
interferingnon-target contaminants. This limits the choices of cleanupoptions.Anumber of
sample extractionmethods canbe applied to these compounds, but only themost common
will be addressed in this guide.
LiquidSamples
For liquid samples, either separatory funnel extraction (USEPAMethod3510) or automated
liquid-liquid extraction (USEPAMethod3520)maybe used. Separatory funnel extraction is
faster and less expensive to set up than the othermethods, but it requires continuous operator
attention.Automated liquid-liquid extractors rununattended, but aremore expensive and, if
analyte recovery is lower than allowed, re-extractionby separatory funnelmaybe required.
Alternatively, if the sample forms an emulsion to thedegree that acceptable solvent recovery
is not possible using a separatory funnel, then some sampleswill require automated liquid-
liquid extraction. Solidphase extraction (USEPAMethod3535) also is anoption for aqueous
samples.
For
separatory funnel extraction
,measure up to1Lofwater into a 2L separatory funnel and
adjust the pH to>11using10MNaOH; be careful not to add toomuchbase. Then extract the
sampleby adding60mLof dichloromethane and shaking for twominutes. It is critical to
shake all samples consistentlyor variations in extraction efficiencywill be observed.The best
way to ensure consistency is touse amechanical separatory funnel shaker, as there often is
considerablevariationwithmanual extractions.Allow thedichloromethane layer to settle to
the bottomof the funnel and thendecant that layer into a collectionvessel (i.e., aKurdena
Danish [KD] concentrator, or aTurbovaporRapidvap
®
container if using automated
concentrators). This extraction
step is repeated twicemore toget quantitative recoveryof all
analytes. Collect all three extractions into the same collectionvessel and label as base/neutral.
Then adjust thewater sample to a pHof slightly less than2using sulfuric acid (1:1, v/v).
Avoidover-acidificationbecause it can result in an acidic extract. Repeat extractionprocedure
on thewater sample as described above, collecting extracts in a separate collectionvessel and
labeling it as acid fraction.
It is critical to removewater from the dichloromethane before you concentrate the extract to
final volume.Dichloromethane canhold approximately11mLofwater per liter of
dichloromethane. If thiswater remains in the extract, itwill partitionoutwhen the volume is
reduced. Thiswill result in the dichloromethane boilingoff first, leavingwater in the
collectionvessel, and the formationof a two-layer extract. The analyte recoverieswill be
lower thandesired, and the presence ofwaterwill interferewith theGC analysis.
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