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
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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
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(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
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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
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(d) m/z 130 (CF2SO ) 3
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(c) m/z 99 (FSO ) 3
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(b) m/z 80 (SO ) 3
(a) SIM m/z 499 13.0
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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.
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