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8:2 diPAP (678-41-1)


24 References Were Found:

The "refereed" or "peer review" status of a journal comes from the Ulrichsweb Global Serials Directory (http://ulrichsweb.serialssolutions.com/), as supplied by the publisher. The term refers to the system of critical evaluation of manuscripts/articles by professional colleagues or peers. The content of refereed publications is sanctioned, vetted, or otherwise approved by a peer-review or editorial board. The peer-review and evaluation system is utilized to protect, maintain, and raise the quality of scholarly material published in serials. Publications subject to the referee process are assumed, then, to contain higher quality content than those that are not.
Peer Reviewed Journal Article

High throughput online solid phase extraction-ultra high performance liquid chromatography-tandem mass spectrometry method for polyfluoroalkyl phosphate esters, perfluoroalkyl phosphonates, and other perfluoroalkyl substances in human serum, plasma, and whole blood

Authors: Poothong, S; Lundanes, E; Thomsen, C; Haug, LS (2017) Analytica Chimica Acta 957:10-19. HERO ID: 3875032

[Less] A rapid, sensitive and reliable method was developed for the determination of a broad range of poly- . . . [More] A rapid, sensitive and reliable method was developed for the determination of a broad range of poly- and perfluoroalkyl substances (PFASs) in various blood matrices (serum, plasma, and whole blood), and uses only 50 μL of sample material. The method consists of a rapid protein precipitation by methanol followed by high throughput online solid phase extraction (SPE), ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS), and negative electrospray ionization detection. The method was developed for simultaneous determination of twenty-five PFASs, including polyfluoroalkyl phosphate esters (PAPs; 6:2, 8:2, 6:2/6:2, and 8:2/8:2), perfluoroalkyl phosphonates (PFPAs; C6, C8, and C10), perfluoroalkyl sulfonates (PFSAs; C4, C6, C7, C8, and C10), perfluoroalkyl carboxylates (PFCAs; C5C14), and perfluoroalkyl sulfonamides (FOSAs; C8, N-methyl, and N-ethyl). High linearity of matrix-matched calibration standards (correlation coefficients, R = 0.99-0.999) were obtained in the range of 0.006-45 ng mL(-1) blood. Excellent sensitivity was achieved with method detection limits (MDLs) between 0.0018 and 0.09 ng mL(-1), depending on the compound and matrix. The method was validated for serum, plasma, and whole blood (n = 5 + 5) at six levels in the range 0.0180-30 ng mL(-1). The accuracy (n = 5) was on average 102± 12%. The intermediate precision (n = 10) ranged from 2 to 40% with an average between-batch of analyses difference of 10± 10%. Two human serum samples from a former interlaboratory comparison were analyzed and the differences between the applied method and the consensus values were below ≤22% (n = 5). The method was also successfully applied to samples of human plasma and whole blood with coefficients of variation in the range 0.8-15.2% (n = 5).

The "refereed" or "peer review" status of a journal comes from the Ulrichsweb Global Serials Directory (http://ulrichsweb.serialssolutions.com/), as supplied by the publisher. The term refers to the system of critical evaluation of manuscripts/articles by professional colleagues or peers. The content of refereed publications is sanctioned, vetted, or otherwise approved by a peer-review or editorial board. The peer-review and evaluation system is utilized to protect, maintain, and raise the quality of scholarly material published in serials. Publications subject to the referee process are assumed, then, to contain higher quality content than those that are not.
Peer Reviewed Journal Article

A fast and sensitive method for the simultaneous analysis of a wide range of per- and polyfluoroalkyl substances in indoor dust using on-line solid phase extraction-ultrahigh performance liquid chromatography-time-of-flight-mass spectrometry

Authors: Padilla-Sánchez, JA; Haug, LS (2016) Journal of Chromatography A 1445:36-45. HERO ID: 3360146

[Less] A fast and sensitive method for simultaneous determination of 18 traditional and 6 alternative per- . . . [More] A fast and sensitive method for simultaneous determination of 18 traditional and 6 alternative per- and polyfluoroalkyl substances (PFASs) using solid-liquid extraction (SLE), off-line clean-up using activated carbon and on-line solid phase extraction-ultrahigh performance liquid chromatography-time-of-flight-mass spectrometry (on-line SPE-UHPLC-TOF-MS) was developed. The extraction efficiency was studied and recoveries in range the 58-114% were obtained. Extraction and injection volumes were also optimized to 2mL and 400μL, respectively. The method was validated by spiking dust from a vacuum cleaner bag that had been found to contain low levels of the PFASs in focus. Low method detection limits (MDLs) and method quantification limits (MQLs) in the range 0.008-0.846ngg(-1) and 0.027-2.820ngg(-1) were obtained, respectively. For most of the PFASs, the accuracies were between 70 and 125% in the range from 2 to100ngg(-1) dust. Intra-day and inter-day precisions were in general well below 30%. Analysis of a Standard Reference Material (SRM 2585) showed high accordance with results obtained by other laboratories. Finally, the method was applied to seven indoor dust samples, and PFAS concentrations in the range 0.02-132ngg(-1) were found. The highest median concentrations were observed for some of the alternative PFASs, such as 6:2-diPAP (25ngg(-1)), 8:2-diPAP (49ngg(-1)), and PFOPA (23ngg(-1)), illustrating the importance of inclusion of new PFASs in the analytical methods.

The "refereed" or "peer review" status of a journal comes from the Ulrichsweb Global Serials Directory (http://ulrichsweb.serialssolutions.com/), as supplied by the publisher. The term refers to the system of critical evaluation of manuscripts/articles by professional colleagues or peers. The content of refereed publications is sanctioned, vetted, or otherwise approved by a peer-review or editorial board. The peer-review and evaluation system is utilized to protect, maintain, and raise the quality of scholarly material published in serials. Publications subject to the referee process are assumed, then, to contain higher quality content than those that are not.
Peer Reviewed Journal Article

Poly- and perfluoroalkyl substances (PFASs) in indoor dust and food packaging materials in Egypt: Trends in developed and developing countries

Authors: Shoeib, T; Hassan, Y; Rauert, C; Harner, T (2016) Chemosphere 144:1573-1581. HERO ID: 3363752

[Less] PFASs concentrations in dust samples collected from three microenvironments in Cairo ranged from 1.3 . . . [More] PFASs concentrations in dust samples collected from three microenvironments in Cairo ranged from 1.3 to 69 ng g(-1) with FTOHs being dominant. The 8:2 FTOH was detected in all samples. Among the FOSAs and FOSEs the MeFOSE was dominant while among ionic PFASs, PFOS and PFOA were most prominent. The concentrations of PFASs were among the lowest worldwide. Correlations between worldwide concentrations of PFOS + PFOA and country development indexes highlight higher usage and human exposure in more developed countries. Food packaging was analyzed for PFSAs, PFCAs and PAPs. The 6:2 and 8:2 monoPAPs were found to be above the MDL in 18% of the samples. PFOA was detected in 79% of the samples with median concentration of 2.40 ng g(-1). PFOS was detected in 58% of the samples with median concentration of 0.29 ng g(-1) while PFHxS and PFDS were below detection limit. Different human exposure scenarios were estimated.

The "refereed" or "peer review" status of a journal comes from the Ulrichsweb Global Serials Directory (http://ulrichsweb.serialssolutions.com/), as supplied by the publisher. The term refers to the system of critical evaluation of manuscripts/articles by professional colleagues or peers. The content of refereed publications is sanctioned, vetted, or otherwise approved by a peer-review or editorial board. The peer-review and evaluation system is utilized to protect, maintain, and raise the quality of scholarly material published in serials. Publications subject to the referee process are assumed, then, to contain higher quality content than those that are not.
Peer Reviewed Journal Article

Identification of biomarkers of exposure to FTOHs and PAPs in humans using a targeted and nontargeted analysis approach

Authors: Dagnino, S; Strynar, MJ; Mcmahen, RL; Lau, CS; Ball, C; Garantziotis, S; Webster, TF; Mcclean, MD; Lindstrom, AB (2016) Environmental Science and Technology 50:10216-10225. HERO ID: 3460580

[Less] Although historic perfluorinated compounds are currently under scrutiny and growing regulatory control . . . [More] Although historic perfluorinated compounds are currently under scrutiny and growing regulatory control in the world, little is known about human exposure to other polyfluorinated compounds presently in use. Fluorotelomer alcohols (FTOHs) and polyfluoroalkyl phosphate esters (PAPs) are known to degrade to terminal perfluorinated acids and toxic reactive intermediates through metabolic pathways. Therefore, it is important to characterize their human exposure by the identification of unique biomarkers. With the use of liquid chromatography-mass spectrometry-time-of-flight analysis (LC-MS-TOF), we developed a workflow for the identification of metabolites for the 8:2 FTOH and 8:2 diPAP. Analysis of serum and urine of dosed rats indicated the 8:2 FTOH-sulfate and the 8:2 diPAP as potential biomarkers. These compounds, as well as 25 other fluorinated compounds and metabolites, were analyzed in human serum and urine samples from the general population (n = 100) and office workers (n = 30). The 8:2 FTOH-sulfate was measured for the first time in human samples in 5 to 10% of the serum samples, ranging from 50 to 80 pg/mL. The 8:2 diPAP was measured in 58% of the samples, ranging from 100 to 800 pg/mL. This study indicates the FTOH-sulfate conjugate as a biomarker of exposure to FTOHs and PAPs in humans.

The "refereed" or "peer review" status of a journal comes from the Ulrichsweb Global Serials Directory (http://ulrichsweb.serialssolutions.com/), as supplied by the publisher. The term refers to the system of critical evaluation of manuscripts/articles by professional colleagues or peers. The content of refereed publications is sanctioned, vetted, or otherwise approved by a peer-review or editorial board. The peer-review and evaluation system is utilized to protect, maintain, and raise the quality of scholarly material published in serials. Publications subject to the referee process are assumed, then, to contain higher quality content than those that are not.
Peer Reviewed Journal Article

Are humans exposed to increasing amounts of unidentified organofluorine?

Authors: Yeung, LeoWY; Mabury, SA (2016) HERO ID: 3859917

[Less] Environmental context Polyfluorinated substances are anthropogenic chemicals that have been widely used . . . [More] Environmental context Polyfluorinated substances are anthropogenic chemicals that have been widely used in several industrial and commercial applications. Analysis of human plasma samples collected from Munster in Germany revealed, since the year 2000, increasing amounts and proportion of unidentified organofluorines. The increasing trend of unidentified organofluorines in plasma samples suggests that humans are being exposed to new and unidentified fluorinated products.

Abstract Samples of human plasma (n=122) from two German cities (collected in 1982-2009, excluding 1994) and whole blood (n=47) from seven Chinese cities (collected in 2004) were analysed for 52 polyfluoroalkyl/perfluoroalkyl substances (PFASs) using LC-MS/MS. Quantifiable PFASs included some newly identified and commercially available chemicals PFPAs, PFPiAs, FTSAs, PAPs and di-SAmPAP, metabolites of fluorotelomer-based products (FTCAs/FTUCAs), PFCAs, PFSAs, FASAs and FOSAAs. The blood samples were also analysed for extractable organofluorine (EOF) using total organofluorine combustion ion chromatography (TOF-CIC). Seven more PFASs (C7 and C10 PFSAs, FOSAA, MeFOSAA, EtFOSAA, C13 PFCA and 8:2 FTSA) were detected in the Chinese samples than had been previously reported. For the German samples, PFHpS, FOSA, MeFOSA, EtFOSA, FTSAs (6:2, 8:2), PFPAs (C6, C8) and PFPiAs (C6/C6, C6/C8, C8/C8) were additional chemicals identified that were not measured in the earlier studies. Those newly identified and commercially available PFASs were either at trace levels (pg mL(-1)) or not detected. A mass balance of fluorine between quantifiable PFAS and EOF in the Chinese samples indicated quantifiable PFASs accounted for 31-86% of EOF. For the German samples, the quantifiable PFAS accounted for 52-100% and 57-100% of EOF in Munster and Halle samples respectively. After the year 2000, an increasing amount and proportion of unidentified organofluorine were observed in Munster samples. The increasing trend of unidentified organofluorine in plasma samples suggested humans are being exposed to new and unidentified fluorinated products.

The "refereed" or "peer review" status of a journal comes from the Ulrichsweb Global Serials Directory (http://ulrichsweb.serialssolutions.com/), as supplied by the publisher. The term refers to the system of critical evaluation of manuscripts/articles by professional colleagues or peers. The content of refereed publications is sanctioned, vetted, or otherwise approved by a peer-review or editorial board. The peer-review and evaluation system is utilized to protect, maintain, and raise the quality of scholarly material published in serials. Publications subject to the referee process are assumed, then, to contain higher quality content than those that are not.
Peer Reviewed Journal Article

[Determination of perfluorosulfonate and perfluorocarboxylate precursors in eggs by ultra-highperformance liquid chromatography-mass spectrometry]

Authors: Wang, M; Wang, YX; Yang, L; Li, JG; Zhang, JL; Zhao, YF; Wu, YN (2016) Zhonghua Yufang Yixue Zazhi 50:439-444. HERO ID: 3860068

[Less] OBJECTIVE: To develop a method for the determination of 11 perfluorosulfonate and perfluorocarboxylate . . . [More] OBJECTIVE: To develop a method for the determination of 11 perfluorosulfonate and perfluorocarboxylate precursors in eggs using ultra-high performance liquid chromatography-tandem quadruple mass spectrometry (UPLC-MS/MS).

METHODS: The target compounds of egg were extracted with 100 mmol/L NaOH-acetonitrile /water(90∶10, V/V) by ultrasonic. Then the extract was purified by solid phase extraction (Waters Oasis(@) WAX 6cc) and then eluted with 9% NH4OH in methanol. The target compounds were separated on a Waters ACQUITY(TM) BEH (18)C column (50 mm × 2.1 mm, 1.7 μm) and detected by negative electrospray ionization (ESI(-)) mass spectrometry in multiple reaction monitoring mode (MRM). All compounds were quantified with internal standards. The accuracy, precision and the limits of detection and quantification of the method were evaluated. Then we detected 7 different egg samples from the market.

RESULTS: The average recoveries for the eleven precursors at 3 levels were 74.09%-116.82% and the relative standard deviations were 2.37%-13.62%. The limits of detection (LOD) of the method were in the range of 0.06-1.50 pg/g (wet weight) and the limits of quantification (LOQ) were in the range of 0.15-3.00 pg/g (wet weight). And 5 target compounds were detected in the 7 market samples. 6:2 fluorotelomer sulfonate (6:2 FTS) was detected in all of samples with the concentrations of 1.67-3.11 pg/g. 6:2 fluorotelomer unsaturated acid (FHUEA) and 6:2 disubstituted polyfluoroalkyl phosphate ester (6:2 diPAP) were detected in 6 samples and the concentrations were<LOD-5.11 pg/g and 3.78-9.16 pg/g, respectively. And the concentrations of 8:2 fluorotelomer sulfonate (8:2 FTS) and N-methyl perfluorooctane sulfonamidoacetic acid (N-Me FOSAA) founded in the same sample were 105.78, and 4.95 pg/g, respectively.

CONCLUSION: This method was simple, rapid, and suitable for determination of perfluorosulfonate and perfluorocarboxylate precursors in eggs with high accuracy and sensitivity. It could also be applied to human burden studies of these precursors.

The "refereed" or "peer review" status of a journal comes from the Ulrichsweb Global Serials Directory (http://ulrichsweb.serialssolutions.com/), as supplied by the publisher. The term refers to the system of critical evaluation of manuscripts/articles by professional colleagues or peers. The content of refereed publications is sanctioned, vetted, or otherwise approved by a peer-review or editorial board. The peer-review and evaluation system is utilized to protect, maintain, and raise the quality of scholarly material published in serials. Publications subject to the referee process are assumed, then, to contain higher quality content than those that are not.
Peer Reviewed Journal Article

Perfluoroalkyl Acids (PFAAs) and Selected Precursors in the Baltic Sea Environment: Do Precursors Play a Role in Food Web Accumulation of PFAAs?

Authors: Gebbink, WA; Bignert, A; Berger, U (2016) Environmental Science and Technology 50:6354-6362. HERO ID: 3856868

[Less] The present study examined the presence of perfluoroalkyl acids (PFAAs) and selected precursors in the . . . [More] The present study examined the presence of perfluoroalkyl acids (PFAAs) and selected precursors in the Baltic Sea abiotic environment and guillemot food web, and investigated the relative importance of precursors in food web accumulation of PFAAs. Sediment, water, zooplankton, herring, sprat, and guillemot eggs were analyzed for perfluoroalkane sulfonic acids (PFSAs; C4,6,8,10) and perfluoroalkyl carboxylic acids (PFCAs; C6-15) along with six perfluoro-octane sulfonic acid (PFOS) precursors and 11 polyfluoroalkyl phosphoric acid diesters (diPAPs). FOSA, FOSAA and its methyl and ethyl derivatives (Me- and EtFOSAA), and 6:2/6:2 diPAP were detected in sediment and water. While FOSA and the three FOSAAs were detected in all biota, a total of nine diPAPs were only detected in zooplankton. Concentrations of PFOS precursors and diPAPs exceeded PFOS and PFCA concentrations, respectively, in zooplankton, but not in fish and guillemot eggs. Although PFOS precursors were present at all trophic levels, they appear to play a minor role in food web accumulation of PFOS based on PFOS precursor/PFOS ratios and PFOS and FOSA isomer patterns. The PFCA pattern in fish could not be explained by the intake pattern based on PFCAs and analyzed precursors, that is, diPAPs. Exposure to additional precursors might therefore be a dominant exposure pathway compared to direct PFCA exposure for fish.

The "refereed" or "peer review" status of a journal comes from the Ulrichsweb Global Serials Directory (http://ulrichsweb.serialssolutions.com/), as supplied by the publisher. The term refers to the system of critical evaluation of manuscripts/articles by professional colleagues or peers. The content of refereed publications is sanctioned, vetted, or otherwise approved by a peer-review or editorial board. The peer-review and evaluation system is utilized to protect, maintain, and raise the quality of scholarly material published in serials. Publications subject to the referee process are assumed, then, to contain higher quality content than those that are not.
Peer Reviewed Journal Article

Aerobic biotransformation of polyfluoroalkyl phosphate esters (PAPs) in soil

Authors: Liu, C; Liu, J (2016) Environmental Pollution 212:230-237. HERO ID: 3856871

[Less] Microbial transformation of polyfluoroalkyl phosphate esters (PAPs) into perfluorocarboxylic acids (PFCAs) . . . [More] Microbial transformation of polyfluoroalkyl phosphate esters (PAPs) into perfluorocarboxylic acids (PFCAs) has recently been confirmed to occur in activated sludge and soil. However, there lacks quantitative information about the half-lives of the PAPs and their significance as the precursors to PFCAs. In the present study, the biotransformation of 6:2 and 8:2 diPAP in aerobic soil was investigated in semi-dynamics reactors using improved sample preparation methods. To develop an efficient extraction method for PAPs, six different extraction solvents were compared, and the phenomenon of solvent-enhanced hydrolysis was investigated. It was found that adding acetic acid could enhance the recoveries of the diPAPs and inhibit undesirable hydrolysis during solvent extraction of soil. However 6:2 and 8:2 monoPAPs, which are the first breakdown products from diPAPs, were found to be unstable in the six solvents tested and quickly hydrolyzed to form fluorotelomer alcohols. Therefore reliable measurement of the monoPAPs from a live soil was not achievable. The apparent DT50 values of 6:2 diPAP and 8:2 diPAP biotransformation were estimated to be 12 and > 1000 days, respectively, using a double first-order in parallel model. At the end of incubation of day 112, the major degradation products of 6:2 diPAP were 5:3 fluorotelomer carboxylic acid (5:3 acid, 9.3% by mole), perfluoropentanoic acid (PFPeA, 6.4%) and perfluorohexanoic acid (PFHxA, 6.0%). The primary product of 8:2 diPAP was perfluorooctanoic acid (PFOA, 2.1%). The approximately linear relationship between the half-lives of eleven polyfluoroalkyl and perfluoroalkyl substances (PFASs, including 6:2 and 8:2 diPAPs) that biotransform in aerobic soils and their molecular weights suggested that the molecular weight is a good indicator of the general stability of low-molecular-weight PFAS-based compounds in aerobic soils.

The "refereed" or "peer review" status of a journal comes from the Ulrichsweb Global Serials Directory (http://ulrichsweb.serialssolutions.com/), as supplied by the publisher. The term refers to the system of critical evaluation of manuscripts/articles by professional colleagues or peers. The content of refereed publications is sanctioned, vetted, or otherwise approved by a peer-review or editorial board. The peer-review and evaluation system is utilized to protect, maintain, and raise the quality of scholarly material published in serials. Publications subject to the referee process are assumed, then, to contain higher quality content than those that are not.
Peer Reviewed Journal Article

Uptake of 8:2 perfluoroalkyl phosphate diester and its degradation products by carrot and lettuce from compost-amended soil

Authors: Bizkarguenaga, E; Zabaleta, I; Prieto, A; Fernández, LA; Zuloaga, O (2016) Chemosphere 152:309-317. HERO ID: 3857361

[Less] The present work studied the uptake of 8:2 perfluoroalkyl phosphate diester (diPAP) by two different . . . [More] The present work studied the uptake of 8:2 perfluoroalkyl phosphate diester (diPAP) by two different crops (lettuce and carrot) and two different amended soils. Firstly, the possible degradation of 8:2 diPAP in the absence of crop was studied and 8:2 monoPAP (monophosphate), 8:2 FTCA (saturated fluorotelomer carboxylate), 8:2 FTUCA (unsaturated fluorotelomer carboxylate), 7:3 FTCA (saturated fluorotelomer carboxylate), PFHpA (perfluoroheptanoic acid), PFHxA (perfluorohexanoic acid) and PFOA (perfluorooctanoic acid) were detected. In the presence of crops, different degradation products were detected in the soil and, while PFNA (perfluorononanoic acid), PFHpA, PFHxA, PFPeA (perfluoropentacoic acid), PFBA (perfluorobutanoic acid), 7:3 FTCA and PFOA were determined in the cultivation media when carrot was grown, PFOA was the only degradation product detected in the case of lettuce experiments. Regarding the uptake in carrot, all the degradation products except 7:3 FTCA were translocated from the soil to the carrot. Carrot core, peel and leaves bioconcentration factors, BCFs, were determined for 8:2 diPAP and its degradation products. Values lower than method detection limits for core and low BCFs in peel (0.025-0.042) and leaves (0.028-0.049) were achieved for 8:2 diPAP. Regarding to the degradation products, the higher their water solubility, the higher the plant translocation. In this sense, the lower the carbon chain length of PFCAs, the higher the BCFs determined (PFBA > PFHxA > PFHpA > PFOA > PFNA). In general, lower total BCFs were achieved when the total organic carbon of the soils increased. For lettuce experiments, 8:2 diPAP (0.04-0.18) and PFOA (0.28-1.57) were only determined in lettuce heart.

The "refereed" or "peer review" status of a journal comes from the Ulrichsweb Global Serials Directory (http://ulrichsweb.serialssolutions.com/), as supplied by the publisher. The term refers to the system of critical evaluation of manuscripts/articles by professional colleagues or peers. The content of refereed publications is sanctioned, vetted, or otherwise approved by a peer-review or editorial board. The peer-review and evaluation system is utilized to protect, maintain, and raise the quality of scholarly material published in serials. Publications subject to the referee process are assumed, then, to contain higher quality content than those that are not.
Peer Reviewed Journal Article

Temporal changes (1997-2012) of perfluoroalkyl acids and selected precursors (including isomers) in Swedish human serum

Authors: Gebbink, WA; Glynn, A; Berger, U (2015) Environmental Pollution 199:166-173. HERO ID: 2851000

[Less] Concentrations (including isomer patterns) and temporal changes (1997-2012) of perfluoroalkyl acids . . . [More] Concentrations (including isomer patterns) and temporal changes (1997-2012) of perfluoroalkyl acids (PFAAs) and selected perfluorooctane sulfonate (PFOS) and perfluoroalkyl carboxylic acid (PFCA) precursors were determined in serum samples from Swedish women. Perfluorooctane sulfonamide (FOSA) and perfluorooctane sulfonamidoacetic acid (FOSAA), as well as its N-methyl and N-ethyl derivatives (MeFOSAA and EtFOSAA) were consistently detected. Highest PFOS precursor concentrations were found for EtFOSAA (before year 2000) or MeFOSAA and FOSAA (after 2000). Disappearance half-lives for all PFOS precursors were shorter compared to PFOS. 4:2/6:2 and 6:2/6:2 polyfluoroalkyl phosphate diesters (diPAPs) were detected in <60% of the samples, whereas 6:2/8:2 and 8:2/8:2 diPAPs were detected in >60% of the samples, but showed no significant change in concentrations over time. Linear and sum-branched isomers were quantified separately for three PFAAs and three precursors. Significant changes between 1997 and 2012 in the % linear isomer were observed for PFOA and FOSA (increase) and PFOS (decrease).