The work by Roth et al. concerned the profile of per- and polyfluoroalkyl substances (PFAS) in air-phase samples taken over an aqueous film-forming foam (AFFF) solution.(1) We question the identification of perfluorooctanoate (PFOA) and other perfluorocarboxylates (PFCAs) in the headspace of an AFFF solution. In this comment, PFOA denotes the anionic species of the compounds, whereas PFOA-H denotes the protonated form. Note that Roth et al. did not differentiate between PFOA and PFOA-H.(1) Roth et al. sampled the AFFF headspace with thermal desorption (TD) tube and XAD/PUF samplers and analyzed them using gas chromatography with mass spectrometry (GC-MS) and by liquid chromatography with tandem MS (LC-MS/MS), respectively. Roth et al. also injected a methanolic standard of PFOA-H onto a TD tube for analysis by GC-MS. Finally, a PFOA-H standard was directly injected onto the GC-MS, operated in electron impact mode (EI), which promotes fragmentation. Roth et al. did not report a molecular ion and only reported the retention time and fragmentation pattern for the PFOA-H directly injected onto the GC/MS. They observed mass-to-charge (m/z) 69 (CF₃), 119 (C₂F₅), 131 (C₃F₅), and 169 (C₃F₇),(1,2) which are characteristic of several highly fluorinated subclasses (including fluorotelomer alcohols, perfluoroalkyl iodides, ethyl perfluoroalkane sulfonamides) and, thus, are not unique to PFOA-H/PFOA.(3,4) Moreover, the PFOA-H fragmentation pattern in Figure S3 of Roth et al. does not match the NIST MS spectrum of PFOA-H.(5) In fact, in their Figure S3, perfluoro-1-heptene (PFHP) gave the best match compared to PFOA-H, which gave the sixth best match.(1,6) Although Roth et al. did not report the observed retention time or fragments for the headspace analysis of AFFF or the PFOA-H standard spiked onto the TD tubes, they concluded that PFOA was present, presumably because the retention time and fragments matched that of their directly injected standard. For these reasons, it seems unlikely that Roth et al. detected intact PFOA by TD-GC/MS in the headspace over an AFFF. To investigate the nature of the signal reported by Roth et al., we purchased PFHP from SynQuest Laboratories (Alachua, FL), a mixture of methanolic protonated PFCAs (including PFOA-H) from Wellington Laboratories (Guelph, ON), and PFOA-H from Sigma-Aldrich (St. Louis, MO). The PFOA-H was prepared in pH 6 water so it could speciate to form anionic PFOA. Separate TD tubes were spiked with individual solutions of PFHP, PFOA-H, and PFOA and then desorbed using our TD-GC-MS system, operated in EI. The observed retention times of PFHP, PFOA-H, and PFOA were practically indistinguishable (∼6 min), and the fragmentation patterns of these compounds were similar (Figure 1). The predicted boiling points of PFHP (74.9 °C), PFOA-H (188 °C), and PFOA (192 °C) from the U.S. EPA CompTox Dashboard(7) indicate that PFHP should elute earlier than PFOA-H/PFOA, yet all peaks for the three separate chemicals eluted at the same time (Figure 1). A second set of tubes identical to the first was analyzed by TD-GC-MS in positive and negative chemical (soft) ionization mode, which often preserves the molecular ion. While we observed m/z 331 and 293 (data not shown), we did not observe the molecular ion of PFOA-H/PFOA, which further puts into question the PFOA identification by Roth et al. To the best of our knowledge, a derivatization step is needed for the determination of PFCAs by GC-MS.(3,8−11) Figure 1. Chromatograms and MS fragmentation patterns of PFHP, PFOA-H, and PFOA following separate spikings to the individual TD tubes and subsequent GC-MS analysis. The same TD desorption method (300 °C for 8 min), GC column (60 m, 0.25 mm I.D., 1.4 μm film thickness DB-VRX, generously donated by Agilent), and MS mode (EI) as found in Roth et al. were used. The cold-trapping system in our TD is a general purpose hydrophobic trap (U-T2GPH-2S, Markes International, Gold River, CA), which is different than what was used in Roth et al. Additional peaks in the PFOA-H chromatogram likely correspond to perfluoro-1-hexene (retention time: 5.1 min) and aldehyde (retention time: 6.8 min.). The fragmentation pattern of PFOA also included m/z 231 (C₅F₉), 281 (C₆F₁₁), and 331 (C₇F₁₃) (data not shown). Roth et al. attributed signals/peaks to PFOA, but it is more likely that they detected PFHP. On the basis of injected PFOA-H/PFOA standards to different TD tubes, the signals observed by Roth et al. are consistent with the degradation of PFOA-H/PFOA to PFHP. In the case of the PFOA-H standard injected to the GC-MS, we hypothesize that the high temperature of Roth et al.’s GC’s inlet (actual inlet temperature not reported) resulted in the thermal degradation of PFOA-H to PFHP. The reaction is presumably very rapid since the residence time of the injected standard is very short (seconds). Similarly, in the case of the headspace analysis of the methanolic PFOA-H standard by TD, the 8 min desorption at 300 °C likely led to the degradation of PFOA-H to PFHP. We could not verify whether the thermal degradation of PFOA-H in the samples from the gas phase above the AFFF also occurred. However, thermal degradations of PFCAs, both protonated and anionic forms, were previously catalogued,(12−15) which led us to believe that the signal observed by Roth et al. in their sample could have originated as PFOA in the AFFF but was thermally degraded to PFHP. Furthermore, although these other thermal decomposition processes differ from TD-GC-MS, PFHP was consistently identified as a thermal byproduct of PFOA-H/PFOA.(12−15) Therefore, even if there was PFOA in the gas phase above AFFF, the compound was thermally degraded to PFHP upon desorption. The presence of m/z 44 (Figure 1), which is the mass of CO₂, is consistent with the decarboxylation of PFCAs.(2) If PFOA-H is misidentified as PFHP, it is likely that the other PFCAs reported by Roth et al. are misidentified since they also likely undergo thermal degradation in a manner similar to PFOA. In fact, we observed additional peaks for the PFOA-H standard, which was purchased as a mixture, unlike for the PFOA standard, which was generated from pure PFOA-H generated by placing it in water. For example, the peak at 5.1 min had m/z 69, 131, and 169 fragments (data not shown) and likely corresponds to perfluoro-1-hexene; however, a standard was not purchased to confirm its identity. Roth et al. indicates that their AFFF was manufactured by Chemguard, which is an AFFF formulator that utilizes telomer-based PFAS,(16,17) within the past two years (2018–2020).(1) The new directive on AFFF MilSpec in 2017 capped the presence of PFOA in AFFF at 800 ppb, which corresponds to a maximum of 13,200 μg PFOA/m.(3)^,(18,19) Roth et al. did not analyze the AFFF solution for PFCAs by LC-MS/MS prior to the experiment; therefore, the concentration of PFOA in the AFFF solution was unknown. One could argue that Roth et al. detected volatile PFOA-H. However, due to the low pK_a of PFOA, −0.5 or 3.8,(20,21) PFOA occurs more than 99.9% in its anionic form in commercial mixtures such as AFFF. Roth et al. estimated the percent of the volatile PFOA-H as extremely small (5 × 10^–7 to 2 × 10^–4; Table S9). Thus, if the measured 13,670 μg/m³ was attributed to measurement of volatile PFOA-H, the total concentration (PFOA and PFOA-H) in the AFFF would be orders of magnitude higher than the allowable limit.(18,19) Furthermore, Roth et al. did not detect PFOA in the LC-MS/MS analysis. For these reasons, it is unlikely that Roth was detecting volatile PFOA-H. Alternatively, Chemguard and other fluorotelomer-based AFFFs contain mg/L levels of fluorotelomer-based PFAS, including fluorotelomer thioamido sulfonates (FtTAoS).(16,17) Depending on the conditions in the AFFF headspace chamber, Roth et al. may have generated and captured aerosols containing nonvolatile PFAS, such as FtTAoS, by the TD system. The thermal degradation of FtTAoS and other fluorotelomer-based PFAS have not been characterized for their potential to form unsaturated fluoroalkenes. In addition, we cannot rule out that PFHP is present in the AFFF formulation itself. The implications of misattributing signals from unsaturated fluoroalkenes to PFCAs is important considering that PFHP is predicted to be bioaccumulative, carcinogenic, and persistent by the European Chemical Agency.(22) More detailed analyses of air samples by TD-GC/MS are needed to resolve the ongoing discussions(23−25) regarding the actual disposition of PFCAs and other nonvolatile PFASs in gas and particle phases. The authors declare no competing financial interest. This publication was made possible by grant RD83960 from the United States Environmental Protection Agency (U.S. EPA). Its contents are solely the responsibility of the authors and do not necessarily represent the official view of the U.S. EPA. This article references 25 other publications.

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关于“从成膜泡沫中释放挥发性全氟和多氟烷基物质的评论”

罗斯等人的工作。关注在成膜泡沫（AFFF）水溶液上采集的气相样品中全氟烷基物质和多氟烷基物质（PFAS）的概况。（1）我们质疑在全氟辛酸（PFOA）和其他全氟羧酸盐（PFCA）中的鉴定AFFF解决方案的顶空。在此评论中，PFOA表示化合物的阴离子种类，而PFOA-H表示质子化形式。注意罗斯等。没有区分PFOA和PFOA-H。（1）Roth等。使用热脱附（TD）管和XAD / PUF采样器对AFFF顶部空间进行了采样，并分别使用了质谱联用的气相色谱仪（GC-MS）和串联质谱联用的液相色谱仪（LC-MS / MS）对它们进行了分析。罗斯等。还将甲醇标准品PFOA-H注入到TD管上，以通过GC-MS分析。最后，将PFOA-H标准品直接注入到GC-MS上，以电子碰撞模式（EI）操作，促进碎片化。罗斯等。没有报告分子离子，仅报告了直接注入GC / MS的PFOA-H的保留时间和碎片化模式。他们观察到质荷比（m / z）69（CF ₃），119（C ₂ F ₅），131（C ₃ F ₅）和169（C ₃ F ₇），（1,2），它们是几种高度氟化的亚类（包括氟调聚物醇，全氟烷基碘化物，乙基全氟烷磺酰胺）的特征，因此并不是PFOA-H / PFOA所独有的。（3,4）此外，PFOA Roth等人的图S3中的-H片段化模式。与PFOA-H的NIST MS谱图不匹配。（5）实际上，在图S3中，与全氟-1-庚烯（PFHP）相比，PFOA-H的匹配度最佳，PFOA-H的匹配度排名第六。 ，6）虽然罗斯等。他们没有报告观察到的保留时间或对AFFF或加到TD管上的PFOA-H标准品的顶空分析的碎片，他们得出结论说存在PFOA，大概是因为保留时间和碎片与直接注入的标准品相符。由于这些原因，Roth等人似乎不太可能。通过TD-GC / MS在AFFF的顶部空间检测到完整的PFOA。为了研究Roth等人报道的信号的性质，我们从SynQuest Laboratories（佛罗里达州Alachua）购买了PFHP，这是从Wellington Laboratories（Guelph，ON）购得的甲醇质子化PFCA（包括PFOA-H）和PFOA- H来自Sigma-Aldrich（密苏里州圣路易斯）。PFOA-H是在pH 6的水中制备的，因此可以形成阴离子PFOA。将单独的TD管分别注入PFHP，PFOA-H和PFOA的各种溶液，然后使用在EI中运行的TD-GC-MS系统进行解吸。观察到的PFHP，PFOA-H和PFOA的保留时间几乎无法区分（约6分钟），并且这些化合物的碎片化模式相似（图1）。来自美国的PFHP（74.9°C），PFOA-H（188°C）和PFOA（192°C）的预测沸点 EPA CompTox仪表板（7）指出，PFHP的洗脱时间应早于PFOA-H / PFOA，但三种不同化学品的所有峰均同时洗脱（图1）。通过TD-GC-MS在正离子和负离子化学（软）电离模式下分析了与第一套相同的第二套管，该方法通常会保留分子离子。虽然我们观察到m / z在331和293（数据未显示）中，我们没有观察到PFOA-H / PFOA的分子离子，这进一步使Roth等人鉴定PFOA成为问题。据我们所知，通过GC-MS测定PFCA时需要进行衍生化步骤。（3,8-11）图1.分别加标后，PFHP，PFOA-H和PFOA的色谱图和MS碎裂模式各个TD管以及随后的GC-MS分析。相同的TD解吸方法（300°C，8分钟），GC柱（60 m，0.25 mm内径，1.4μm膜厚DB-VRX，由安捷伦慷慨捐赠）和MS模式（EI）在Roth等人中发现。被使用。我们的TD中的冷阱系统是通用疏水阱（U-T2GPH-2S，Markes International，Gold River，CA），与Roth等人使用的疏水阱不同。PFOA-H色谱图中的其他峰可能对应于全氟-1-己烯（保留时间：5.1分钟）和醛（保留时间：6.8分钟）。PFOA的碎片化模式也包括在内m / z 231（C ₅ F ₉），281（C ₆ F ₁₁）和331（C ₇ F ₁₃）（数据未显示）。罗斯等。将信号/峰值归因于PFOA，但是他们更有可能检测到PFHP。在将PFOA-H / PFOA标样注入不同的TD管的基础上，Roth等人观察到了信号。与PFOA-H / PFOA降解为PFHP一致。对于注入到GC-MS中的PFOA-H标准品，我们假设Roth等人的GC进样口的高温（未报告实际的进样口温度）导致PFOA-H热降解为PFHP。由于注入的标准液的停留时间非常短（秒），因此反应可能非常快。同样，在通过TD对甲醇PFOA-H标准品进行顶空分析的情况下，在300°C下解吸8分钟可能会导致PFOA-H降解为PFHP。我们无法验证AFFF以上气相中样品中PFOA-H的热降解是否也会发生。但是，先前已对质子化和阴离子形式的PFCA的热降解进行了分类（12-15），这使我们相信Roth等人观察到的信号。他们的样品中的三聚氰胺可能起源于AFFF中的PFOA，但被热降解为PFHP。此外，尽管这些其他的热分解过程不同于TD-GC-MS，但始终将PFHP鉴定为PFOA-H / PFOA的热副产物。（12-15）因此，即使气相中AFFF以上存在PFOA，解吸后，该化合物热降解为PFHP。存在的 （12-15）使我们相信Roth等人观察到的信号。他们的样品中的三聚氰胺可能起源于AFFF中的PFOA，但被热降解为PFHP。此外，尽管这些其他的热分解过程不同于TD-GC-MS，但始终将PFHP鉴定为PFOA-H / PFOA的热副产物。（12-15）因此，即使在AFFF以上的气相中存在PFOA，解吸后，该化合物热降解为PFHP。存在的 （12-15）使我们相信Roth等人观察到的信号。他们的样品中的三聚氰胺可能起源于AFFF中的PFOA，但被热降解为PFHP。此外，尽管这些其他的热分解过程不同于TD-GC-MS，但始终将PFHP鉴定为PFOA-H / PFOA的热副产物。（12-15）因此，即使在AFFF以上的气相中存在PFOA，解吸后，该化合物热降解为PFHP。存在的 即使在AFFF以上的气相中存在PFOA，该化合物在脱附后也会热降解为PFHP。存在的 即使在AFFF以上的气相中存在PFOA，该化合物在脱附后也会热降解为PFHP。存在的m / z 44（图1）是CO ₂的质量，与PFCA的脱羧作用是一致的。（2）如果PFOA-H被误认为是PFHP，则Roth等人报道的其他PFCA很有可能。由于它们也可能以类似于PFOA的方式经历热降解，因此被误识别。实际上，我们观察到PFOA-H标准品的其他峰，该标准品是作为混合物购买的，与PFOA标准品不同，它是通过将纯净的PFOA-H放入水中而生成的。例如，在5.1分钟的峰的m / z69、131和169片段（数据未显示），可能对应于全氟-1-己烯；但是，没有购买标准来确认其身份。罗斯等。表示他们的AFFF由Chemguard制造，后者是AFFF的制定者，在过去两年（2018-2020）内使用基于端粒的PFAS（16,17）。（1）2017年AFFF MilSpec的新指令限制了AFFF中存在PFOA的浓度为800 ppb，对应于最大13,200μgPFOA / m。（3）^，（18,19）Roth等。实验前未通过LC-MS / MS分析PFCA的AFFF解决方案；因此，AFFF溶液中PFOA的浓度未知。有人可能会说罗斯等人。检测到挥发性PFOA-H。但是，由于p K _a低PFOA的-0.5或3.8，（20,21）中，PFOA以阴离子形式在商业混合物（如AFFF）中的发生率超过99.9％。罗斯等。估计挥发性PFOA-H的百分比非常小（5×10 ^–7至2×10 ^–4；表S9）。因此，如果测得13,670μg/ m ³归因于挥发性PFOA-H的测量，AFFF中的总浓度（PFOA和PFOA-H）会比允许限值高几个数量级。（18,19）在LC-MS / MS分析中未检测到PFOA。由于这些原因，Roth不太可能检测到挥发性PFOA-H。或者，Chemguard和其他基于氟调聚物的AFFF包含mg / L的基于氟调聚物的PFAS，包括氟调聚物硫酰胺基磺酸盐（FtTAoS）。（16,17）取决于AFFF顶空室中的条件，Roth等。可能由TD系统生成并捕获了包含非挥发性PFAS（例如FtTAoS）的气溶胶。FtTAoS和其他基于氟调聚物的PFAS的热降解尚未形成潜在的形成不饱和氟烯烃的特征。此外，我们不能排除AFFF配方本身中存在PFHP。考虑到PFHP被欧洲化学局预测为具有生物蓄积性，致癌性和持久性，因此将不饱和氟代烯烃信号误分配给PFCA的意义非常重要。（22）需要通过TD-GC / MS对空气样品进行更详细的分析才能解决有关在气相和颗粒相中PFCA和其他非挥发性PFAS的实际配置的正在进行的讨论（23-25）。作者宣称没有竞争性的经济利益。该出版物是由美国环境保护署（US EPA）提供的RD83960资助的。其内容仅由作者负责，并不一定代表美国EPA的正式观点。本文引用了其他25个出版物。