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LCGC VOLUME 19 NUMBER 11 NOVEMBER 2001
Sample Prep
Perspectives
Guest Author
Greg LeBlanc
Collecting, preserving,
and preparing samples
are critical to producing
accurate and reliable
results in the analysis of
organic compounds. This
“Sample Prep
Perspectives” column
reviews sample
preparation techniques
that are available to
organic laboratories
under SW-846 regulations
for the analysis of nonand semivolatile
compounds from
environmental samples.
Ronald E. Majors
Sample Prep Perspectives Editor
www.chromatographyonline.com
A Review of EPA
Sample Preparation
Techniques for
Organic Compound Analysis
of Liquid and Solid Samples
E
nvironmental analysis often involves
analytes in a wide variety of matrices,
ranging from air to sewage water to
polluted soil samples. Proper sample preparation procedures are necessary to achieve
optimum analytical results. The U.S. Environmental Protection Agency (EPA) is the
government body responsible for the definition, development, and enforcement of
analytical measurements for specific pollutants that are deemed to be harmful to the
environment. The EPA’s Test Methods for
Evaluating Solid Waste — SW-846 — provides a comprehensive source of information about sampling, sample preparation,
analysis, and reporting for compliance with
the Resource Conservation and Recovery
Act. Furthermore, SW-846 outlines test
procedures used to characterize solid waste
in accordance with 40 Code of Federal Regulations (CFR) Part 261, Identification and
Listing of Hazardous Waste. The sample
preparation and analytical procedures or
determinative steps are categorized by the
analyte, either inorganic or organic.
Inorganic analyte procedures are characterized by acid digestion steps using conventional or microwave heating (3000
series methods), followed by atomic absorption or emission spectroscopy (6000 and
7000 series methods). Inorganic analysts are
concerned with approximately 30 analytes
or elements for environmental analysis.
Organic analyte procedures are characterized by solvent extraction steps for
nonvolatile and semivolatile analytes (3500
series methods) and postextraction cleanup
(3600 series methods). Sample preparation
methods for volatile compounds define
methodologies such as purge-and-trap, distillation, headspace, or dilution in the 5000
series methods. The analytical steps are gas
chromatography (GC) (8000–8200 series
methods), high performance liquid chromatography (HPLC) (8300 series methods), and GC–Fourier transform infrared
(8400 series methods). Organic analysts are
concerned with more than 450 analytes.
Compared with inorganic analytical laboratories, organic laboratories face a major
challenge to cost-effectively prepare and
analyze the wide variety of analytes from
environmental samples. As with any
process, the primary focus is on the determinative step that produces the result.
However, the front-end work of sampling,
preservation, and sample preparation is critical to producing accurate and reliable
results. In this report, I will review the sample preparation techniques — 3500 and
3600 series methods — that are available to
organic laboratories under SW-846 for the
analysis of non- and semivolatile compounds from environmental samples. The
3500 series methods cover the extraction
steps, and the 3600 series methods include
the cleanup steps.
Extraction Techniques
The sample matrix and analytes define
the 3500 series sample extraction methods.
The matrix is aqueous, solid, an air sampling train, or nonaqueous soluble. The
analytes are characterized as either non- or
semivolatile organic compounds. All samples analyzed for nonvolatile or semivolatile
organic compounds require a solvent
extraction step, with the exception of
nonaqueous solvent–soluble samples. The
solvent-soluble samples use a simple solvent
dilution step, a so-called dilute-and-shoot
method. Because both solid and liquid
samples are injected as an extracted liquid,
I first will discuss sample preparation techniques for solid samples and later those for
aqueous samples.
NOVEMBER 2001 LCGC VOLUME 19 NUMBER 11
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Solid samples: The technologies used
for the extraction of non- and semivolatile
organic compounds from solid samples are
more diverse than for water and other liquid samples. The techniques vary by the
(a)
(b)
(c)
Figure 1: Three-step extraction procedure
using the Foss-Tecator Soxtec Avanti automated extraction system. Shown are (a) the solubilization of extractable matter from sample
immersed in boiling solvent, (b) rinsing of
extracted solvent (similar to conventional Soxhlet extraction), and (c) concentration of the
extracted sample by evaporation and collection
of distilled solvent for reuse or disposal. During
evaporation, solvent is blocked from returning
to the extraction cup and flows into a collection tank. (Courtesy of Foss North America,
Eden Prairie, Minnesota.)
method used to enhance the action of the
solvent for the extraction. They range from
classic Soxhlet extraction to modern microwave extraction. For this discussion, I will
define a solid sample as clay, soil, sludge,
sediment, or waste.
Soxhlet extraction (EPA Method 3540C):
Analytical chemists have used Soxhlet
extraction for more than 100 years (1).
This method is the classic approach to
extracting solid samples for a spectrum of
non- and semivolatile organic compounds.
It works in a manner analogous to continuous liquid–liquid extraction, except the
sample is solid instead of liquid. The sample, held in a porous cellulose thimble, is
extracted continuously with a fresh aliquot
of distilled and condensed solvent. Thus,
the extraction is performed at temperatures
below the solvent’s boiling point. In practice, the method is simple to perform. The
technique is time consuming but can be
automated, and it has a low acquisition
cost. Typically, the extraction step requires
16–24 h at 4–6 cycles/h.
Automated Soxhlet extraction (EPA
Method 3541): This technique is an automated version of the classic Soxhlet
approach to extracting solid samples, with
two modifications (Figure 1). This
approach initially immerses the thimble
that contains the sample directly into the
boiling solvent. Then, the thimble is
moved above the solvent to mimic the
rinse-extraction step of Soxhlet extraction.
Finally, a concentration step using modern
automated equipment reduces the final vol-
Load sample
into cell
Fill cell
with solvent
Pump
Heat and
pressurize cell
Hold sample at pressure and temperature
Pump clean solvent
into sample cell
Purge solvent from
cell with nitrogen gas
Solvent
Oven
Extraction
cell
Vent
Nitrogen
Collection vial
Extract ready
for analysis
Figure 2: Schematic diagram of a pressurized-fluid extraction system. (Courtesy of Dionex Corp.,
Sunnyvale, California.)
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ume to 1–2 mL. This three-stage approach
shortens the extraction step to 2 h, because
it provides direct contact between the sample and solvent at the solvent’s boiling
point. It also reduces the consumption of
solvent. For more details about automated
Soxhlet extraction, please see Arment’s
review (1).
Pressurized-fluid extraction (EPA Method
3545A): Pressurized-fluid extraction is one
of the latest technologies to be approved for
solid-sample extraction. The method performs extractions at elevated solvent temperatures and pressures to achieve performance comparable to the Soxhlet technique
with a significant reduction in time and solvent consumption. The instrumentation to
perform pressurized-fluid extraction, more
commonly known by its trade name of
accelerated solvent extraction, is semiautomated (see Figure 2). After loading a sample into the extraction cell and sealing it,
the instrument performs the extraction,
separation, and collection steps automatically. Samples are processed sequentially in
batches of as many as 24 samples. Equipment is available that will perform the
extraction of six samples simultaneously
(2).
The principle of pressurized-fluid extraction is simple. The sample (or a sample
mixed with a drying agent) is loaded into a
high-pressure, high-temperature extraction
cell, which is sealed. The cell is heated to
the extraction temperature, which often is
two- to threefold the atmospheric boiling
point of the solvent; the extracting solvent
is added and held in contact with the sample for 5–10 min; the extract then is
flushed from the cell into the collection
vessel with a volume equal to 60–75% of
the cell volume; and finally the extract is
purged with nitrogen. In pressurized-fluid
extraction, the sample is diluted by the volume of extraction solvent and must be concentrated before analysis. For more details
about the pressurized-fluid extraction technique, please see the review by Richter (3).
Microwave extraction (EPA Method
3546): Microwave extraction is the latest
technique to be included in SW-846. The
microwave extraction method is the process
of heating solid sample-solvent mixtures in
a sealed (closed) vessel with microwave
energy under temperature-controlled conditions. Although used less frequently, the
extraction also can be performed in an
open vessel at atmospheric pressure. Figure
3 depicts a typical microwave extraction cell
used in a closed extraction system. This system provides significant temperature elevation above the atmospheric boiling point of
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LCGC VOLUME 19 NUMBER 11 NOVEMBER 2001
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the solvent, accelerates the extraction
process, and yields performance comparable to the standard Soxhlet method. Samples are processed in batches of as many as
14 samples per run. The microwave energy
provides very rapid heating of the sample
batch to the elevated temperatures, which
shortens the extraction time to 10–20 min
per batch. Solvent consumption is only
25–50 mL per sample. After the heating
cycle is complete, the samples are cooled
and the sample is filtered to separate the
sample from the extract for the analytical
step. The technique was reviewed in
LCGC (4).
Ultrasonic extraction (EPA Method
3550C): This method uses mechanical
energy in the form of a shearing action,
which is produced by a low-frequency
sound wave. The sample is immersed in an
ultrasonic bath with solvent and subjected
to ultrasonic radiation for 2–3 min. The
sample is separated from the extract by
vacuum filtration or centrifugation. The
process is repeated 2–3 times, and the
extracts are combined for the analytical
step. This technique has the benefit of
shortened extraction times, but it sacrifices
performance relative to the Soxhlet technique. The solvent receives only minor
heating of a few degrees above room temperature and, thus, cannot provide as thorough extraction of difficult matrices such
as aged soil samples.
Supercritical fluid extraction (EPA Methods 3560, 3561, and 3562): These three
methods use supercritical carbon dioxide
or carbon dioxide with a modifier to
extract total recoverable hydrocarbons,
polycyclic aromatic hydrocarbons (PAHs),
polychlorinated biphenyls (PCBs), and
organochlorine pesticides. Supercritical carbon dioxide or carbon dioxide–organic
modifier extracts the sample, which is held
in an extraction vessel within a closed system. Supercritical fluids such as carbon
dioxide have properties of both liquids and
gases, which make them desirable for
extraction. When its temperature and pressure are controlled, carbon dioxide has the
penetrating characteristics of gases and the
solvating properties of liquids. An organic
modifier such as methanol, acetonitrile,
or isopropanol can be used to assist the
extraction of polar analytes. The primary
operating parameters are the carbon dioxide or carbon dioxide–modifier flow rates,
temperature, pressure, and dynamic or static mode of extraction.
Figure 4 shows a schematic of a typical
supercritical fluid extraction (SFE) system.
In the static mode, the extraction cell fills
the extraction vessel with the supercritical
fluid and holds it in the vessel for a specified period of time. In the dynamic mode,
the supercritical fluid passes through the
extraction vessel continuously. The depressurized carbon dioxide or carbon dioxide–
modifier exits the system, and the target
compounds are collected in a vessel that
contains a suitable solvent or sorbent material. For more information about SFE,
consult reference 5.
Comparison of solid sample extraction
techniques: Table I compares the EPA sample preparation methods for solid samples.
It compares the above techniques with
regard to solvent use, extraction time,
acquisition costs, and operating costs.
Clearly, the modern techniques provide
more rapid extraction with a minimal
amount of organic solvent required. However, some of them are expensive compared
with the classic methods.
Aqueous samples: Several solvent
extraction techniques for the analysis of
non- and semivolatile organic compounds
in a liquid state are available under SW846. Separatory funnel liquid–liquid
extraction, continuous liquid–liquid
extraction, and solid-phase extraction
(SPE) techniques most often are used for
liquid matrices. The solvents used for
liquid–liquid extraction techniques are
insoluble in the aqueous sample. The techniques are applicable for the extraction of
water-insoluble and slightly water-soluble
organic compounds.
Separatory funnel liquid–liquid extraction
(EPA Method 3510C): This technique is a
classic approach to extraction for liquid
samples for a spectrum of non- and semi-
Temperature probe
Cryogenic zone 4
Cryogenic zone 3
Restrictor
Seal
cover
Liner
Chamber
with
sample
Cryogenic
zone 2
Cryogenic zone 1
Impinged surface
or region
Preheat
Microwave
energy
Carbon
dioxide pump
Sample
and
solvent
Liquid carbon dioxide
Vessel support
module
Extraction
Figure 3: Sample and solvent in a
GreenChem extraction vessel. Contents are
rapidly heated to elevated temperatures and
pressures using microwave energy. (Courtesy of
CEM Corp., Matthews, North Carolina.)
Expansion Collection
Reconstitution
Figure 4: Schematic diagram of a generic SFE system showing four cryogenic zones. (Courtesy
of Agilent Technologies, Wilmington, Delaware.)
NOVEMBER 2001 LCGC VOLUME 19 NUMBER 11
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Table I: Comparison of 3500 series extraction techniques for solid samples*
EPA Method Number
Extraction Technique
3540B
3541
3545A
3546
3550C
3560, 3561, and 3562†
Soxhlet
Automated Soxhlet
Pressurized-fluid extraction
Microwave-accelerated extraction
Ultrasonic nebulization
SFE
Average Solvent Use
(mL/sample)
Average Extraction
Time (min/sample)
300
50
10–30
25–40
300
10
960–1440
120
10–15
10–20
30
20–50
Acquisition Cost
Operating Cost
per Sample
Very low
Very high
Moderate
Low to moderate
High
Low
Moderate
Low
Low
High
Moderate to high Moderate to high
* Examples of solid samples include soils, sediments, fly ashes, sludges, and solid wastes that are amenable to extraction with conventional solvents.
† SFE is limited to the analysis of total recoverable hydrocarbons, PAHs, organochlorine pesticides, and PCBs.
volatile organic compounds. An aqueous
sample is mixed in a separatory funnel
with an immiscible organic solvent that is
denser than water. After standing, the mixture will separate into two phases with the
analytes partitioning toward the organic
phase. The solvent is drawn off and saved,
and the extraction step is repeated multiple
times. The solvent extracts are combined
for the analytical step. For a basic discussion of liquid–liquid extraction, please see
reference 6.
Continuous liquid–liquid extraction (EPA
Method 3520C): This technique is an automated version of the separatory funnel
technique for a spectrum of non- and
semivolatile organic compounds. Figure 5
illustrates the construction principles of
two types of continuous liquid–liquid
extraction systems. The solvent is added to
the top of a liquid–liquid extractor, which
contains the aqueous sample. The solvent
extracts the analytes as it passes through
the sample. The extract is collected in a
boiling flask and distilled, and fresh solvent
is sent to the top of the extractor to create
a continuous process. This process runs for
12–24 h, and it is used in situations in
which large sample sizes with low analyte
concentrations are needed. The extract
contained in the boiling flask is used for
the analytical step.
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Solid-phase extraction (EPA Method
3535C): This extraction technique for
aqueous samples is the latest to be added
to the SW-846 manual, and it involves the
most recent advances in technology. SPE
isolates analytes using the same principles
as those used in liquid chromatography,
though much less efficiently. As Figure 6
depicts, in SPE, compounds are retained
and eluted as a mobile phase transports
them over a stationary phase (sorbent) that
has been conditioned with an organic solvent to activate it. In the most common
use of SPE, the mobile phase is the aqueous sample to retain the analytes onto the
sorbent. This step is followed with a solu-
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LCGC VOLUME 19 NUMBER 11 NOVEMBER 2001
bilizing solvent as the mobile phase to
elute the analytes, which are collected for
analysis.
The SPE packing is housed in a cartridge or disk. The cartridge is a disposable
syringe with a frit on each end of the packing, and the disk is a membrane filter. The
smaller length-to-diameter ratio of a disk
allows greater flow and extraction rates relative to the cartridges.
www.chromatographyonline.com
This technique’s benefits are that it significantly reduces extraction times and solvent consumption and has a concentration
step. With automated filtering systems,
multiple samples can be processed simultaneously. The downside of SPE is the cost
of the cartridges and disks. For a series of
reviews of various aspects of SPE, please
see reference 7.
Postextraction Handling
and Cleanup
(a)
Condenser
Condensed
solvent
Concentrated
solutes
Solute solution
Heating mantle
(b)
Condenser
Condensed
solvent
After the extraction step, chemists rarely
perform analysis directly without further
sample handling. Postextraction handling
includes steps as simple as sample–extract
separation, water removal, and solvent
exchange or a more involved, multiplestep cleanup. The cleanup methods are
designed to remove interferences that cause
poor analytical results and increased analytical instrument downtime. Postextraction
handling steps are dependent upon the
matrix, the analytes of interest, and the
solvent.
Sample–extract separation: The objective is to separate the original matrix from
the extract. Two approaches are available:
filtration and centrifugation.
Filtration: The sample–extract mixture is
passed through a filter to remove the solid
sample from the solvent. Fresh solvent
washes the solid sample on the filter to
ensure all the analyte goes into the collected solvent. Two or three wash steps can
be used with minimal solvent to prevent
further dilution.
Centrifugation: The sample–extract
mixture is centrifuged, and the extract is
decanted and removed. The residual sample is washed two or three times with minimal solvent to prevent further dilution.
Water removal: Water is extremely polar
and will adversely affect most column
packing materials, especially GC stationary
phases and some normal-phase HPLC
packings. Therefore, analysts should
remove water from the extract before
injecting it into the analyzer. A common
technique to remove any water from the
sample or extract is to pass it over anhydrous sodium sulfate. The sodium sulfate
is a water scavenger, and it will dry the
sample solvent without absorbing any of
the analyte of interest. Sodium sulfate
water removal usually is performed in conjunction with a filtration step. The sodium
sulfate is added to the filter before filtering
the sample–extract mixture. Another
approach is to mix and swirl the sodium
sulfate with the mixture solution before filtration.
Solvent concentration: This technique
concentrates the analyte of interest, so the
analytical signal intensity is increased. This
task is performed by evaporating the solvent to a 1–2 mL volume and then making
it up to a 5-mL volume in a volumetric
flask or GC–HPLC vials. Automatic solvent concentration systems are commercially available.
Solvent exchange: This technique separates the extracted molecules by their
polarity to eliminate extraneous peaks in
subsequent analysis or to move the analytes
to a different solvent that is more compatible with the subsequent analytical technique. Solvent exchange is performed as a
liquid–liquid extraction in a separatory
funnel. This step is one most analysts
would prefer to avoid. However, they may
need an aggressive solvent to extract the
analytes from the matrix and remove extraneous analytes. Sometimes, a polar solvent
Solute
solution
(a)
Conditioning
solvent
Concentrated
solutes
A A A
I I A I IA
I A I AI I
I IA I IAA IA
I AI A I A
A AA
(c)
Collection
reservoir
(d)
Sample
Washing
solvent
Analytes
SPE
cartridge
Heating mantle
(b)
A A AA
A
A
AA A
A A AAA
A A AA
I II I
II I
I II I I I I
I
I II II I
I I I
Interference
Figure 5: Schematics of a continuous liquid–
liquid extraction system in which the extraction
solvent is (a) less dense and (b) more dense
than the solution from which the solute is
being extracted.
Eluting
solvent
A A A AA
A
A
AAAA A A
Analytes
Figure 6: Steps in an SPE experiment: (a) sorbent conditioning; (b) sample loading; (c) washing,
in which the analytes are retained and the interferences are washed into the collection reservoir;
and (d) elution, in which the analytes are eluted with a strong solvent.
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LCGC VOLUME 19 NUMBER 11 NOVEMBER 2001
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is necessary to remove the analytes of interest that can not be used in the chromatographic analysis.
The cleanup methods are covered by the
3600 series methods of SW-846 (see Table
II). They include adsorption chromatography to separate compounds based on differences in polarity, gel-permeation chromatography to remove interferences with
high molecular weights or high boiling
points, acid–base partitioning to separate
acidic or basic organic compounds from
neutral ones, and oxidation of interfering
components with acids, alkalis, and oxidizing agents.
Adsorption chromatography: This technique is used to separate analytes of a relatively narrow polarity range from interfering peaks of different polarity. Adsorption
chromatography is used primarily for the
cleanup of nonpolar compounds such as
organochlorine pesticides and PAHs. In
addition to removing interferences, adsorption chromatography can be used to fractionate complex mixtures of analytes.
Gel-permeation chromatography: This
technique is used to remove high molecular weight or high-boiling-point interferences from the target compounds. High
molecular weight compounds can contami-
Table II: 3600 series cleanup method summary
EPA Method Method Name
Number
(Technique)
Objective
Procedure
Comments
3610B
Alumina cleanup
(adsorption
chromatography)
To separate analytes from
interfering compounds of
different polarity
Elute sample through basic- to
neutral-pH alumina with
suitable solvents to leave
interfering compounds on the
column
Suitable for extracts that contain
nitrosamines and phthalate
esters
3611B
Alumina column
cleanup and separation
of petroleum wastes
(adsorption
chromatography)
To separate petroleum
waste extracts into base–
neutral aliphatic,
aromatic, and polar
fractions
Elute sample through neutral-pH
alumina with suitable solvents
to leave interfering compounds
on the column
Not recommended for extracting
petroleum wastes with
predominantly polar solvents;
perform acid–base partition
cleanup on extract before
alumina cleanup
3620C
Florisil cleanup*
(adsorption
chromatography)
To separate analytes from
interfering compounds of
different polarity or
fractionate groups of
target compounds
Elute extract through Florisil to
leave interfering compounds on
the column or cartridge or to
fractionate target compounds
Suitable for extracts that contain
aniline and its derivatives,
chlorinated hydrocarbons,
haloethers, nitroaromatics,
nitrosamines, organochlorine
and organophosphorus pesticides,
organophosphates, PCBs, and
phthalate esters
3630C
Silica-gel cleanup†
(adsorption
chromatography)
To separate analytes from
interfering compounds of
different polarity
Elute extract through silica gel to
leave interfering compounds on
the column or cartridge
Primary use is for extracts that
contain PAHs, derivatized
phenolic compounds,
organochlorine pesticides, and
PCBs
3640A
Size separation (sizeexclusion
chromatography)
To remove high molecular
weight, high-boiling-point
materials from target
analytes
Elute extract through column
packed with hydrophobic gels of
varying pore sizes to separate its
components by molecular weight
Universal technique for
semivolatile organic compounds
and pesticides
3650B
Acid–base partition
cleanup (liquid–liquid
partitioning)
To separate acid analytes
from base to neutral
analytes in petroleum
waste extracts
Mix extract with methylene
chloride and water at pH 12–13
in separatory funnel; separate
aqueous (acidic) and organic
(base to neutral) fractions
Useful for separating neutral PAHs
from acidic phenols; base–neutral
fraction may require an alumina
column cleanup before analysis
3660B
Sulfur cleanup
(oxidation and
reduction)
To eliminate sulfur from an
extract and prevent the
masking of organochlorine
pesticides and organophosphorus pesticides in
GC analysis
Mix sample with either copper or
tetrabutylammonium sulfite,
shake, and separate the sample
from the sulfur cleanup reagent
Sulfur has solubility characteristics
similar to organochlorine and
organophosphorus pesticides;
typically used for sediment,
marine algae, and industrial
waste samples
3665A
Sulfuric acid–
permanganate cleanup
(oxidation and
reduction)
To decompose organic
compounds that cause
baseline elevation or
complex chromatograms
and prevent the accurate
quantitation of PCBs
Exchange extracting solvent with
hexane, sequentially treat with
98% sulfuric acid and, if
necessary, 5% potassium
permanganate
Decomposes most other organic
chemicals, so it is not applicable
for other target analytes
* Florisil is magnesium silicate with basic properties.
† Sulfuric acid with sodium silicate.
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nate HPLC columns and be difficult to
remove by washing. High-boiling-point
compounds can contaminate GC injection
ports and column heads, thus requiring
more instrument maintenance. Gelpermeation chromatography, also known
as size-exclusion chromatography, is the
most universal cleanup method for semivolatile organic compounds and pesticides.
Acid–base partitioning: This technique
is used to separate neutral PAHs from the
acidic PAHs that can appear in petroleum
waste samples. Acid–base partitioning also
can be used to fractionate base–neutral
compounds.
Oxidation of interfering components:
Copper or tetrabutylammonium sulfite is
used to eliminate the sulfur contamination
that can mask pesticide peaks in certain
GC detectors. Sulfuric acid and potassium
permanganate are used to oxidize organic
compounds that cause interferences for
PCB analysis. Oxidation is a very rigorous
but nonspecific technique.
Summary
Sample preparation is a critical step in the
overall process of obtaining reliable and
accurate data, especially in the environmental analysis of nonvolatile and semivolatile organic compounds. Extraction
techniques are devised to remove a spectrum of compounds. This removal requires
subsequent handling and cleanup of the
extract before analytical measurement.
In this “Sample Prep Perspectives” column, I attempted to review the extraction
and cleanup techniques available to analysts according to SW-846 requirements for
nonvolatile and semivolatile organic compounds. I have observed a noticeable
improvement in sample preparation capabilities with SW-846’s inclusion of extraction techniques such as SPE for aqueous
samples and pressurized-fluid extraction,
SFE, and microwave extraction for solid
samples. These newer methods reduce
extraction times and solvent consumption.
References
(1) S. Arment, Current Trends and Developments in
Sample Preparation, LCGC 17(6S), S38–S42
(1999).
(2) R.E. Majors, Current Trends and Developments
in Sample Preparation, LCGC 17(6S), S8–S13
(1999).
(3) B.E. Richter, Current Trends and Developments
in Sample Preparation, LCGC 17(6S), S22–S28
(1999).
(4) G. LeBlanc, Current Trends and Developments
in Sample Preparation, LCGC 17(6S), S30–S37
(1999).
(5) J.M. Levy, Current Trends and Developments in
Sample Preparation, LCGC 17(6S), S14–S21
(1999).
(6) R.E. Majors, LCGC 14(11), 936–943 (1996).
(7) R.E. Majors, Current Trends and Developments
in Sample Preparation, LCGC May 1998,
S8–S15 (1998).
Greg LeBlanc is the new business development manager at CEM Corp., P.O. Box 200,
Matthews, NC 28106-0200, e-mail
[email protected].
Ronald E. Majors
“Sample Prep Perspectives” editor
Ronald E. Majors is
business development manager, consumables and accessories business unit,
Agilent Technologies,
Wilmington, Delaware, and is a member of LCGC’s editorial advisory board. Direct
correspondence about this column to “Sample
Prep Perspectives,” LCGC, 859 Willamette
Street, Eugene, OR 97401, e-mail lcgcedit@
lcgcmag.com.
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