Researchers
need better tools
to get to the bottom
of the contamination
mystery.
KURUNTHACHALAM KANNAN
STATE UNIVERSITY OF NEW YORK
AT ALBANY
URS BERGER
NORWEGIAN INSTITUTE FOR
AIR RESEARCH
PIM DE VOOGT
UNIVERSITY OF AMSTERDAM
(THE NETHERLANDS)
JENNIFER FIELD
OREGON STATE UNIVERSITY
JAMES FRANKLIN
SOLVAY
J O H N P. G I E S Y
MICHIGAN STATE UNIVERSITY
TOM HARNER
DEREK C. G. MUIR
BRIAN SCOTT
ENVIRONMENT CANADA
MARY KAISER
DUPONT
ULF JÄRNBERG
STOCKHOLM UNIVERSITY
(SWEDEN)
KEVIN C. JONES
LANCASTER UNIVERSITY (U.K.)
SCOTT A. MABURY
UNIVERSITY OF TORONTO
(CANADA)
HORST SCHROEDER
RWTH AACHEN (GERMANY)
M AT T S I M C I K
UNIVERSITY OF MINNESOTA
C H R I S T I N A S OT TA N I
SALVATORE MAUGERI
FOUNDATION (ITALY)
B E RT VA N B AV E L
ANNA KÄRRMAN
GUNILLA LINDSTRÖM
ÖREBRO UNIVERSITY (SWEDEN)
S T E FA N VA N L E E U W E N
NETHERLANDS INSTITUTE FOR
FISHERIES RESEARCH
© 2004 American Chemical Society
ore than three decades ago, Taves and
co-workers first postulated that perfluoroalkyl substances were widespread environmental contaminants
(1, 2). They used arduous, yet elegant,
methods to extract, clean up, and detect organic fluorine in human serum with nuclear
magnetic resonance (NMR) spectroscopy. These first
studies revealed compounds that resembled perfluorooctanoic acid (PFOA), but the inherent ambiguity
of the detection system prevented definitive identification. In addition, the low concentration, lack of
authentic standards, and unusual physical and chemical properties of perfluoroalkyl chemicals made it
difficult to confirm their identity by traditional techniques, such as gas chromatography/mass spectrometry (GC/MS).
Researchers remained uncertain until 2001, when
a new method confirmed that humans indeed had
PFOA and other perfluoroalkyl substances in their
blood. When other groups applied these analytical
methods to monitoring global wildlife samples a short
time later, they determined that many of the compounds had become globally distributed (4, 5). For example, in the blood of Arctic animals, perfluorooctane
sulfonate (PFOS) ranked among the most prominent
organohalogen contaminants (5 ).
Given that existing and future data are likely to be
used as a basis for regulatory decisions that could impact the economy, industry, and the general health of
humans and ecosystems, researchers have the responsibility to ensure that the published data are accurate,
precise, and reproducible. Standard reference materials (SRMs) and standardized analytical methods exist
for many organochlorine compounds but, unfortunately, few cover perfluoroalkyl substances. In the interest of future data quality and sound regulatory
decisions, many of the world’s scientists researching
perfluoroalkyl substances met in Hamburg, Germany,
in May 2003 to openly discuss and share information
on the current approaches and perceived problems
with analytical techniques. This article summarizes the
main recommendations derived from that workshop.
M
Perfluoroalkyls persist worldwide
Much of what we know about perfluoroalkyl compounds should be credited to advances in liquid chromatography–electrospray tandem mass spectrometry
(HPLC/MS/MS). Using this approach, Hansen et al.
confirmed Taves and co-workers’ speculation—that
human blood indeed contained nanogram-per-milliliter concentrations of PFOA. They also found similar
concentrations of PFOS, perfluorohexane sulfonate,
and perfluorooctane sulfonamide in these samples (3).
Perfluoroalkyl substances include a broad range of
ionic and neutral compounds that contain a perfluorinated alkyl moiety. These compounds have many
uses but have primarily been manufactured as the
surface active ingredients for soil and liquid repellents that coat paper, textiles, leather, and carpeting
PHOTODISC
J O N AT H A N W. M A R T I N
UNIVERSITY OF TORONTO
(CANADA)
JULY 1, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 249A
FIGURE 1
Perfluoroalkyl literature publications skyrocket
The peer-reviewed, open-literature publications that report the fate,
toxicological effects, and environmental concentrations of perfluoroalkyl and polyfluoroalkyl substances increased rapidly in the past few
years, according to keyword searches in CAplus and MEDLINE for C8,
C10, PFOS, PFOA, perfluorinated, and perfluoroalkyl.
50
Number of publications
45
40
35
30
25
20
15
10
2002
2000
1998
1996
1994
1992
1990
1988
1986
1984
1982
0
1980
5
Year
(6). Widespread detection of PFOS quickly prompted
the manufacturer 3M to voluntarily phase out production of perfluorooctyl sulfonyl surfactant chemistries in 2001. More recently, agencies in several
countries that regulate the manufacture and use of
chemicals and international institutions such as the
U.S. EPA, Environment Canada, and the European
community have begun inventorying the use of perfluoroalkyl substances, assessing their potential risks,
and considering regulations or bans on the future use
of these compounds.
For example, suspecting that PFOS may represent
a significant hazard to human and environmental
health, EPA imposed a Significant New Use Rule controlling the import and domestic manufacture of PFOS
and perfluorooctanyl sulfonamides (7). However, despite detection in human serum and wildlife tissues,
PFOA and longer-chain perfluoroalkyl carboxylates
(PFCAs; 3, 5, 8) continue to be manufactured as polymer additives. Industry cites a lack of suitable replacements as the reason (9).
Such uses have recently come under scrutiny because of concern that PFOA was found in maternal
blood and in children (10). EPA has appealed to the
research community for more data regarding the effects and sources of PFOA in humans (10). Given that
perfluorinated acids have no known mode of environmental degradation and are bioaccumulative
when the perfluoroalkyl chain exceeds six carbons
(11), a genuine demand exists for more research on
their thresholds and mechanisms of toxicity, the magnitude and extent of human and environmental exposure, and their sources to the environment.
In the past three years, the number of peer-reviewed publications reporting the fate, toxicological
effects, and environmental concentrations of perfluoroalkyl substances increased 10-fold (Figure 1). These
crucial early reports have proven exceedingly valuable in highlighting the need for more research.
However, the existing literature is not sufficient to accurately evaluate the environmental and human
health risks of perfluoroalkyl substances. Although
the science continues to rush forward, many experts
have acknowledged that the current analytical methods and tools for quantification of perfluoroalkyl substances are limited or only in their infancy, which
restricts further research aimed at understanding their
sources and environmental dynamics.
Needed: Good chemical standards
FIGURE 2
Short-chain perfluorinated acid impurities detected
in a commercial standard of PFTA by HPLC/MS/MS
Percentages represent the area counts of the integrated peak area
relative to the sum of all three peak areas. Such impurities result in a
negative bias of unknown proportion in quantitation when mixed
standard solutions are used without correction.
9000
8000
7000
94% PFTA
(m/z 713, C13F27COO–)
6000
5000
3% PFDoA
(m/z 13, C11F23COO–)
4000
3000
3% PFDA
(m/z 513, C9F19COO–)
2000
1000
0
15
15.5
16
16.5
17
17.5
18
18.5
19
19.5
Retention time (min)
250A ■ ENVIRONMENTAL SCIENCE & TECHNOLOGY / JULY 1, 2004
20
The demand is greater than ever for laboratories reporting measurements or effects of perfluoroalkyl
substances to provide accurate, precise, and reproducible data. This is a challenge because, although
chemical standards are available from several manufacturers, the products have variable purity and isomer profiles and many standards do not exist or are
difficult to obtain.
Ideally, the impurities in all perfluoroalkyl standards would be characterized centrally before they are
distributed. For example, a number of commercial
suppliers sell PFOS standards but industry has also
given some as gifts. In the published literature, the
purity of PFOS standards ranges from 86% to more than
98% or may even be unreported. The impurities are not
well documented, but perfluoroalkyl standards commonly contain various short-chain analogues. For example, a standard of perfluorotetradecanoic acid (PFTA)
(ABCR, Karlsruhe, Germany, 96%) contained significant quantities of both perfluorododecanoic (PFDoA)
and perfluorodecanoic acid (PFDA, 3% impurity on
the basis of area count; Figure 2). Such impurities are
problematic because they contribute to a negative bias
when mixed standard solutions are used in quantitation. Fluorochemical standards manufacturers are ad-
FIGURE 3
HPLC/MS chromatograms of a PFOS
standard
(a) This mass chromatogram of PFOS (Fluka, Buchs,
Switzerland, K+ salt, 98% purity; m/z 499) from a selected ion-monitoring (SIM) experiment shows nine distinct
structural isomers. (b–e) Extracted mass chromatograms from a full-scan product ion MS/MS experiment
(i.e., m/z 499 → scan) demonstrate that the fragmentation of different isomers, produced by collision-induced
dissociation, differs significantly and would introduce a
bias in routine PFOS analyses. Chromatography was
performed on a C18 reversed-phase column at 0.2 mL
min–1 using a water:methanol (2 mM ammonium acetate) linear gradient elution program: 0 min, 50:50; 12
min, 15:85; 20 min, 15:85.
–
(e) m/z 169 (CF3CF2CF )
2
–
(d) m/z 130 (CF2SO )
3
–
(c) m/z 99 (FSO )
3
–
(b) m/z 80 (SO )
3
(a) SIM m/z 499
13.0
13.5
14.0
14.5
15.0
Retention time (min)
vised to use methods for purity determination that
differentiate impurities of differing chain-length (e.g.,
such as HPLC/MS/MS), because traditional methods
for distinguishing them, such as infrared absorption,
may be inadequate.
Perfluoroalkyl chains can be manufactured by two
processes—electrochemical fluorination and telomerization—which result in significantly different isomeric profiles and contribute further to the variability
of authentic standards (6, 12). Electrochemical fluorination yields many branched isomers (e.g., 70% normal chain PFOS; 13), whereas telomerized products
are predominantly linear (more than 98%). It is widely assumed that electrochemical processes generate
perfluoroalkyl sulfonyl-based chemicals such as
PFOS. However, the process leading to all other perfluoroalkyl standards remains largely ambiguous, and
chemical suppliers do not provide this information.
Slight modification to the chromatographic conditions commonly used in routine analysis of perfluorinated acids will reveal the structural isomers of PFOS
(m/z 499, Figure 3a). Isomers respond to electrospray
ionization (ESI) differently, and thus the relative areas
in the chromatogram do not necessarily reflect the relative amounts in the standard. However, the major
peak is presumed to be the normal-chain isomer.
Although which peak corresponds to which structural isomer is unknown, the type of branching patterns
present in a typical batch of PFOS was identified by
using NMR analysis (Figure 4; 13).
In the interest of analytical precision, such chromatographic separation is commonly avoided so that
all isomers will elute simultaneously and a total concentration can be reported by integrating a single
chromatographic peak. Although this approach may
be convenient, it imposes a systematic bias of unknown proportions on the accuracy, unless the relative amounts of branched isomers in the sample are
identical to the analytical standard. For example, in
routine PFOS analysis using HPLC/MS/MS, it is common to quantify on the basis of the m/z 499 → 99
mass transition. However, not all PFOS isomers actually yield a product ion at m/z 99 (Figure 3c). The
total analytical bias would presumably be a combination of differential isomeric ESI efficiencies and
fragmentation patterns. Thus, this hidden systematic error contributes to a lack of accuracy in either
HPLC/MS or HPLC/MS/MS modes of analysis if the
isomer-specific data are undetermined.
Even in MS/MS mode, the potential exists for mass
interference. Although m/z 80 is the most abundant
product ion formed from the fragmentation of PFOS,
m/z 99 has always been used for quantitation. This
fact is due to a reported mass interference in some
animal species (particularly birds), whose retention
time is indistinguishable from PFOS. The interference
has a m/z of 499 and a common product ion at m/z
80 (3). Researchers should be aware of similar interferences for other perfluoroalkyl substances and take
steps to identify them. For example, more than one
product ion should be monitored per analyte to avoid
false-positive detection or overestimated concentrations and so that the relative response can be compared with an authentic standard. In the case of PFOS,
both the 499 → 99 m/z and 499 → 80 m/z transitions
are suggested.
Improving chromatographic separation and
quantitation
Perfluoroalkyl isomers may also be important from a
toxicological and environmental fate perspective. Like
the estrogenic activity of branched versus linear isomers of nonylphenol (14), perfluoroalkyl isomers may
have different toxicological profiles. Furthermore,
many environmentally relevant physical and chemical properties, including bioaccumulation potential,
octanol–water partition coefficient (Kow), vapor pressure, and water solubility, are expected to be affected by perfluoroalkyl branching and could lead to
significantly different transport and partitioning behavior in the environment. For these reasons, future
efforts must aim at improving chromatographic
resolution of perfluoroalkyl isomers, producing pure
perfluoroalkyl isomer standards, and/or further characterizing the isomer content of existing standards.
Such advancements would allow for true analytical
accuracy while simultaneously providing the tools
with which to resolve many uncertainties related to
environmental behavior and toxicology of perfluoroalkyl substances.
JULY 1, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 251A
FIGURE 4
Structures of the impurities
These normal-chain and branched isomers were present in a typical batch of the potassium salt of PFOS and were
identified by using 19F-NMR analysis.
ESI is currently indispensable for identifying and
quantifying perfluorinated acids; however, this
method has some inherent limitations. In particular,
coeluting matrix components can either suppress or
enhance ionization, which must be controlled to
achieve maximum accuracy. Matrix-matched standards are one possible control measure but become
impractical when an appropriate “clean” matrix cannot be found. In biota analysis, using a matrix from
a different species may not be valid and could introduce further variability to the data.
Standard addition quantitation, which involves
spiking successive known quantities of a standard
into the sample and reanalyzing, is common in atomic absorption spectroscopy and an acceptable technique to use when matrix effects are unavoidable.
Successive spiking has already proven necessary for
perfluorinated acid quantitation by direct-inject MS
analysis (15). No comprehensive study has demonstrated that ionization is suppressed during chromatographic analysis of perfluorinated acids by
HPLC/MS/MS, but researchers should be wary of this
possibility. Unfortunately, standard addition quantitation can place further demands on instrument and
sample preparation time but should be used for ac252A ■ ENVIRONMENTAL SCIENCE & TECHNOLOGY / JULY 1, 2004
curacy when spike/recovery experiments indicate a
problem. The poor recoveries reported in past analyses may reflect ionization suppression rather than
problems with the extraction method.
Current sample preparation methods do not include a cleanup step (e.g., for removing lipids), thus
the potential for ionization suppression remains very
high in complex environmental and biological samples. Therefore, an effective cleanup method that
would selectively remove interferences from perfluoroalkyl substances is desirable. Solid-phase extraction methods with C18 or fluorous silica adsorbent
show some promise and should be explored further.
Isotopically labeled perfluoroalkyl internal standards (isotope dilution) are probably the most appropriate approach for negating ionization effects
because they will have the same retention times as
their natural analogues (excluding any isomeric separation). The only potential problem is that the overall method sensitivity may be reduced by ionization
suppression caused by the internal standard, but limiting the amount used can presumably control this.
The most immediate and urgent research need is
availability of one or more mass-enriched perfluorinated acids (i.e., 13C and/or 18O PFOS or PFOA) to
A general paucity of
chemical standards
limits the feasibility
and breadth of many
investigations.
may be used as an internal standard for the analysis
of another perfluorinated acid. For environmental
biota samples, short perfluorinated acids, such as perfluoroheptanoic acid (5), are suitable because they
do not bioconcentrate (11) and are not prominent
contaminants in the food web. Analysts should prescreen their samples for traces of their internal standard to ensure it is not a contaminant itself.
QA and QC
Contamination or analyte loss at all stages of collecserve as a common internal standard among all labtion and analysis can make analyzing perfluoroalkyl
oratories currently measuring perfluorinated acids.
compounds difficult; thus field blanks, matrix blanks,
Perfluorooctanoic acid [1,2-13C] is now available from
and reagent blanks are highly recommended. AlPerkinElmer Life Sciences, Inc (Boston, MA). Ideally,
though perfluorinated acids will not degrade under
the mass enrichment should be more than 1 amu to
any reasonable storage conditions, samples should
minimize overlap with natural isotopes. Toxicological
always remain refrigerated or frozen to avoid degraand environmental fate studies and extraction
dation of molecules that may be precursors to permethod validation also require radioactive perfluorifluorinated acids. For example, telomer alcohols can
nated acid standards (e.g., 14C PFOS). Overall, a genbiodegrade to PFCAs (17 ), and perfluorooctanyl suleral paucity of chemical standards limits the feasibility
fonamides can biodegrade to PFOS (18). Some reand breadth of many investigations. Table 1 lists prisearchers suggest using clean room conditions to
ority fluorochemical standards required for analyzing
analyze neutral polyfluorinated alcohols because they
perfluoroalkyl substances.
exist in the open atmosphere (19). However, perfluoAlthough many researchers continue to quantify
rinated acid can be successfully analyzed in a conperfluoroalkyl substances by external calibration,
ventional laboratory by taking certain precautions.
analysts should use the most appropriate internal
For example, because some perfluorinated acids such
standard available, which may depend
on the application. Ideally, the internal
TA B L E 1
standard should respond at a reasonably constant ratio to the analyte across
Priority list of needed perfluoroalkyl standards
a wide concentration range. With elecDots indicate that the native or isotopically labeled form is currently unavailable.
trospray analysis, in which response
can be highly dependent on chemical
Remarks
properties, another perfluoroalkyl inCompound
Native Labeled (References)
ternal standard is warranted because
Perfluorinated acids
of the many unique physical and chemPFOS (C8F17SO–3 )
•
Internal standard
ical properties imparted by perfluorina*
PFOA
(CF
(CF
)
CO
H)
•
Internal standard
tion. Published reports have relied on
3
26
2
PFNA (CF3(CF2)7CO2H)
•
Internal standard
hydrocarbon acids (15) and polyfluoriPerfluorohexane sulfonate (C6F13SO–3 )
•
Contaminant (3)
nated internal standards for quantitaPerfluorodecane sulfonate (C10F21SO–3 )
•
Contaminant (27 )
tion (3), including the telomer sulfonate
Perfluorotridecanoate
(CF
(CF
)
CO
H)
•
Contaminant (5 )
1-H,1-H,2-H,2-H-tetrahydroperfluo3
2 11
2
Perfluoropentadecanoate (CF3(CF2)13CO2H)
•
Contaminant (5 )
rooctane sulfonate (THPFOS). However,
Perfluoroalkyl sulfonamides
these standards are currently recognized
Perfluorooctane sulfonamide (C8F17SO2NH2)
•
Contaminant (3)
as poor choices because of their low
N-methyl
perfluorooctane
sulfonamidoethanol
acidity and surface activity relative to
(C8F17SO2N(CH3)CH2CH2OH)
•
Contaminant (19)
perfluorinated acids, and THPFOS is
N-ethyl perfluorooctane sulfonamidoethanol
also an environmental contaminant
(C8F17SO2N(C2H5)CH2CH2OH)
•
Contaminant (19)
(16). Short-chain perfluorinated dicarPerfluorooctane
sulfonamido
boxylic acids are useful in water sample
acetic acid (C8F17SO2N(H)CH2CO2H)
•
Metabolite (28)
analysis but are presumably less hydroN-methyl perfluorooctane sulfonamido
phobic and surface-active than most
acetic acid (C8F17SO2N(CH3)CH2CO2H)
•
Metabolite (29)
perfluoroalkyl analytes of interest (16).
N-ethyl
perfluorooctane
sulfonamido
A better alternative may be 7H-dodecacetic acid (C8F17SO2N(C2H5)CH2CO2H)
•
Metabolite (28)
afluoroheptanoic acid because the
Telomerized products
hydrogen is not adjacent to the acid
Fluorotelomer acids
function. Its only drawback is that the
(Cx F2x+1CH2CO2H; x = 6, 8, 10)
•
•
Metabolite (30 )
compound fragments differently from
Fluorotelomer aldehydes
other perfluorinated carboxylic acids
(Cx F2x+1CH2CHO; x = 6, 8, 10)
•
•
Biodegradation
(i.e., loss of hydrofluoric acid, in addiproduct
(5, 31)
tion to decarboxylation).
For non-environmental monitoring
applications, one perfluorinated acid
* Perfluorooctanoic acid [1,2-13C] is available from PerkinElmer Life Sciences, Inc. (Boston, MA).
JULY 1, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 253A
as PFOS irreversibly adsorb to glass, most laboratories have switched to using polypropylene. No consensus has been reached on the behavior of PFOA,
PFCAs, or neutral polyfluorinated substances, but analysts should test for adsorption to containers.
Contamination sources of perfluoroalkyl substances in the laboratory are not well characterized
but presumably are numerous given their current use
in many retail products and common laboratory consumables. One known source of contamination is
fluoropolymers, such as poly(tetrafluoroethylene),
which are present in various laboratory products.
Wherever possible, contact with fluoropolymers during analysis should be avoided because PFCAs are
used as polymerization aids in their manufacture.
Even vial caps contain perfluorinated acid contamination from fluoropolymer (e.g., Teflon) and fluoroelastomer septa (e.g., Viton; 20). Analysts must also
be aware of post-injection contamination on HPLC
systems, which has been consistently reported and
presumably is caused by internal fluoropolymer parts.
Various techniques minimize this contamination,
including replacing fluoropolymer parts with stainless steel and polyetheretherketone, installing an upstream guard column, or simply reducing LC-column
equilibration time. This type of contamination should
be differentiated from injection-port carryover, which
is caused by the injection of high concentrations and
leads to “false” chromatographic peaks appearing in
subsequent injections. A suggested guideline is that
individual injections should not exceed 10 nanograms
on a typical HPLC/MS/MS system to avoid significant problems and that blank (e.g., solvent only) injections should be made after high-concentration
samples or standards to examine for carryover.
Contamination sources
of perfluoroalkyl
substances in the
laboratory are not well
characterized but
presumably are
numerous.
Despite the aforementioned problems plaguing
perfluoroalkyl analyses, analysts should strive to report precision and accuracy with all published data.
Data may take the form of spike and recovery of an
analyte added to the sample matrix (e.g., mean recovery ± relative standard deviation), repetitive analysis of the same sample to demonstrate method
precision (e.g., relative standard deviation), or a comparison of standard curve quantitation to standard
addition analysis. Such ancillary information would
assist those who may use the data for regulatory purposes, such as determining whether the data are
quantitative or semiquantitative.
254A ■ ENVIRONMENTAL SCIENCE & TECHNOLOGY / JULY 1, 2004
Instrumental analysis
Giesy and Kannan reviewed the historical advancements in perfluoroalkyl analytical methods, from early
nonspecific “total-organofluorine” methods through
today’s compound-specific quantitative methods (21).
When researchers select an instrumental method to
analyze perfluoroalkyl substances now, they must
consider a balance between sensitivity and specificity.
By far, the most commonly used instrumental configuration for quantitative determination of perfluoroalkyl substances in environmental matrixes is
HPLC/negative ESI/triple-quadrupole MS/MS. However, some other methods may be more useful under
certain circumstances and should be explored.
For example, a recent report analyzes PFOS in river
water with HPLC/MS using a photoionization source
in place of electrospray (22). Photoionization may be
less sensitive than electrospray for perfluorinated acid
analysis, but the technique remains promising because it is less prone to matrix effects. Future efforts
should emphasize testing photoionization sources
with other perfluoroalkyl substances in more complex matrixes with MS/MS detection.
Single-quadrupole HPLC/MS can be a sensitive
technique for perfluoroalkyl substance analysis. Yet
the technique’s applicability for analyzing complex
matrixes remains dubious because of lower selectivity, particularly for PFOS analysis where known mass
interference exists. For HPLC/MS to gain popularity,
an effective cleanup method that can remove all interferences is needed.
Ion trap mass-analyzers can also perform tandem
analysis, including MSn experiments, which is an inherent advantage over triple-quadrupole systems.
Unfortunately, ion traps cannot be used for MS/MS
analysis of PFOS because of the large mass difference
between the parent ion (m/z 499) and the product ion
(m/z 99). However, ion trap technology can indeed be
useful for environmental monitoring of PFCAs because
collision-induced dissociation results in decarboxylation (i.e., M–44 m/z). Nevertheless, a method that can
detect both PFCAs and sulfonates is preferable.
Quadrupole/time-of-flight (QTOF) mass analyzers
have provided qualitative, high-resolution evidence
for the identification of numerous perfluoroalkyl substances in the environment (3, 5), yet are not used
more widely in routine monitoring applications. This
limitation has largely been due to lower sensitivity
and linear range than those of triple-quadrupole MS
systems.
Some perfluoroalkyl substances cannot be easily
protonated or deprotonated in solution, and thus may
not be directly amenable to ESI and LC analysis. Such
substances include perfluorooctanyl sulfonamides of
secondary amines (i.e., CF3(CF2)xSO2N(R)(R´), where
R and R´ are not hydrogen). These substances are directly amenable to GC/MS analysis using electron
ionization or chemical ionization (CI; 19, 23, 24), although the positive CI mode offers higher sensitivity
and specificity resulting from an abundant pseudomolecular ion (i.e., [M+H]+). GC/MS methods have
been used to monitor for airborne perfluoroalkyl substances (19), but even these methods could benefit
from a cleanup step.
Interlaboratory comparison
With numerous methodological and instrumental options available for perfluoroalkyl analysis, and many
laboratories currently reporting results, an urgent
need persists for a coordinated evaluation of method
performance. The accurate measurement of trace
pollutant concentrations greatly benefits from an interlaboratory calibration (25). For perfluoroalkyl substances, one option may be an informal system
whereby independent laboratories purchase and analyze an existing SRM, as has recently been initiated
for brominated flame retardants (26). The U.S. National Institute of Standards and Technology and the
European Community’s Bureau Communautaire de
Référence (BCR) maintain and distribute various naturally contaminated SRMs that have certified pollutant concentration, such as PCBs. However, presently
no data exist on perfluoroalkyl substances in any
SRM. Several SRMs—including human liver (SRM
4352), human serum (SRM 1952), Lake Superior fish
tissue (SRM 1946), herring (BCR 718), and sewage
sludge (BCR 088)—may be appropriate for perfluoroalkyl analysis.
An urgent need persists
for a coordinated
evaluation of method
performance.
A more formal approach would involve a centrally
organized “round robin”-type analysis, and The
Netherlands Institute for Fisheries Research is currently
organizing one for perfluoroalkyl substances. The
round robin will consist of two stages. Phase 1 will distribute standard solutions of unknown concentration
to each laboratory so that instrumental performance
can be evaluated directly without the additional biases that extraction and concentration steps impose. This
information will help minimize systematic calibration
errors in Phase 2 and will evaluate the importance of
standard selection (e.g., manufacturer) in quantitation.
Phase 2 should involve distribution of one or more naturally contaminated matrixes for extraction and analysis by each laboratory (perhaps a SRM) in an effort to
produce a “consensus” matrix and to inform participants of their performance. Several details have yet to
be decided, including what perfluoroalkyl chemicals to
include in the distributed “unknown” solutions, what
internal standards to use, and what matrixes contaminated with a wide variety of perfluoroalkyl substances
to circulate.
Acknowledgments
The authors would like to thank the Fluoropolymers
Committee of the Association of Plastics Manufacturers in Europe (APME) for supporting the PFOA
Workshop in Hamburg.
Jonathan W. Martin is a postdoctoral fellow and Scott A.
Mabury is an associate professor at the University of
Toronto. Kurunthachalam Kannan is an associate professor at the State University of New York at Albany. Urs
Berger is a scientist at the Norweigan Institute for Air
Research. Pim de Voogt is an associate professor at the
University of Amsterdam. Jennifer Field is a professor at
Oregon State University. James Franklin is a senior principal scientist at Solvay. John P. Giesy is a professor at
Michigan State University. Tom Harner, Derek C. G. Muir,
and Brian Scott are all research scientists at Environment
Canada. Mary Kaiser is a research fellow at Dupont. Ulf
Järnberg is a research scientist at Stockholm University.
Kevin C. Jones is a professor at Lancaster University.
Horst Schroeder is a professor at RWTH Aachen. Matt
Simcik is an assistant professor at the University of
Minnesota. Christina Sottani is a chemist assistant at
the Salvatore Maugeri Foundation. Bert van Bavel and
Gunilla Lindström are professors and Anna Kärrman is
a Ph.D. student at Örebro University. Stefan van Leeuwen
is at the Netherlands Institute for Fisheries Research.
References
(1) Taves, D. R. Nature 1968, 217, 1050–1051.
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