Abstract
The scientific foundation for per- and polyfluoroalkyl substances (PFAS) measurements in water, soils, sediments, biosolids, biota, and outdoor air has rapidly expanded; however, there are limited efforts devoted to developing analytical methods to measure vapor-phase PFAS in indoor air. A gas chromatography-tandem mass spectrometry (GC-MS/MS) method coupled with thermal desorption (TD) sorbent tube analysis was developed to quantify trace levels of fluorotelomer alcohols (FTOHs) emitted from consumer products in the indoor environment. Method evaluation included determination of instrument detection limits (IDLs), quality assurance checks of target standards purchased from different vendors, sample loss during storage, and TD sorbent breakthrough with tubes coupled in-series. The IDLs for TD-GC-MS/MS analyses ranged from 0.07 – 0.09 ng/tube. No significant loss of FTOHs was observed during stability tests over 28 days with relative standard deviations (RSDs) of spiked TD tubes ranging from 3.1 – 7.7% and the RSDs of polypropylene copolymer vial storage of standard solutions ranging from 4.3 – 8.4%. TD tube breakthrough was minimal with recovered FTOHs in the second tubes <1% of the spiked concentrations in the first tubes with carrier gas volume up to 20 L. The method has been applied to determine FTOH emissions from three consumer products in micro-scale chambers. A liquid stone cleaner/sealer product contained the highest levels of 6:2, 8:2, and 10:2 FTOHs, while the mattress pad products contained lower levels of 8:2 and 10:2 FTOHs. The emission parameters, including the initial emission factors and first order decay rate constants, were obtained based on the experimental data. The developed methods are sensitive and specific for analysis of all four target FTOHs (4:2, 6:2, 8:2, 10:2 FTOHs) with chamber testing. The methods can be extended to indoor air sampling and could be applicable to ambient air sampling.
Keywords: PFAS, Thermal desorption, Gas chromatography tandem mass spectrometry, Consumer products, Emissions
1. Introduction
The indoor environment can be one of the primary pathways for exposure to per- and polyfluoroalkyl substances (PFAS) for the general population due to direct (i.e., skin contact or ingestion) or indirect exposures (i.e., inhalation of suspended particles and gases) to consumer products and building materials [1–3]. While the research for PFAS contamination and risk management in water, soils, sediments, biosolids, biota, and outdoor air is rapidly expanding [4], there are limited efforts devoted to understanding source, fate, and transport of vapor-phase PFAS in indoor air [1,4].
Fluorotelomer alcohols (FTOHs) are volatile and semivolatile precursors to perfluorinated carboxylic acids and are used in the synthesis of various surfactants and as intermediates in the manufacture for a variety of products including polymers, paints, adhesives, aqueous film-forming foam, waxes, and cleaning agents [5–6]. Although airborne FTOHs have been characterized in occupational settings (e.g., ski waxing, textile manufacturing, and firefighting) [3,6], the residential indoor air burden of FTOHs from consumer products, building materials, and household dust is not well understood [2–3,5–6]. Data for key parameters controlling emissions of FTOHs from consumer products and building materials (i.e., initial concentrations, emission rates, etc.) are still limited in the literature. Thus, it is imperative to develop sampling and analytical methods to characterize FTOHs in indoor air for the development of mass transfer models to quantitatively predict FTOH emissions and transport for exposure assessment and risk management.
There are considerable efforts to develop harmonized and consensus methods for measuring PFAS in various media by governmental agencies, voluntary consensus standards bodies, and researchers worldwide [7–15]. PFAS mixtures are usually quantified by liquid chromatography-mass spectrometry (LC-MS) [16–18]. However, gas chromatography-mass spectrometry (GC-MS) is preferred for targeted analysis of FTOHs due to sensitivity issues arising from ionization and adduct formation with optimal LC-MS chromatographic conditions for concomitantly quantifying other PFAS [5–6,19–26]. Air sampling for FTOHs typically involves passive or active air samplers, such as Isolute® ENV+ solid-phase extraction cartridges, glass-fiber filters and XAD™ resin sandwiched between polyurethane foam (PUF) plugs, and PUF, XAD™, and sorbent impregnated polyurethane disks that require large volumes of air. Solvent extraction must be performed to recover FTOHs from the air sampling media prior to GC-MS analysis [19–23]. Thermal desorption (TD) sorbent tube collection, used in the passive mode with diffusion caps or active mode with pumped/forced air, reduces air sampling volumes and eliminates the added step and variability of solvent extraction. TD tubes can be desorbed with a TD autosampler directly onto GC columns for GC-MS analysis of FTOHs, minimizing sample loss and significantly increasing FTOHs concentrations [6, 24–29]. Recently, gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS) has been used to quantify trace levels of FTOHs in indoor air because of its ability to obtain precursor-to-product mass fragmentation spectra via multiple reaction monitoring (MRM) for higher sensitivity and selectivity. This analytical approach improves reliability and detectability of PFAS in air samples, especially for sampling methods that involve large air volumes or complex matrices [23, 29]. However, there are no published methods for the collection and quantification of airborne FTOHs with a TD autosampler coupled to a GC-MS/MS system. Therefore, a TD-GC-MS/MS analytical method for trace level analysis of FTOHs in indoor air is needed to understand an important uncertainty in current exposure estimates attributed to emissions of PFAS from consumer products and building materials.
This work reports method development for TD-GC-MS/MS analysis of trace levels of FTOH emissions from consumer products as well as GC-MS/MS analysis of FTOHs in solid and liquid consumer products. The following most common FTOHs in the indoor environment were selected for this study: 1H, 1H, 2H, 2H-perfluorohexan-1-ol (4:2 FTOH; CAS No. 2043-47-2), 1H, 1H, 2H, 2H-perfluorooctan-1-ol (6:2 FTOH; CAS No. 647-42-7), 1H, 1H, 2H, 2H-perfluorodecan-1-ol (8:2 FTOH; CAS No. 678-39-7), and 1H, 1H, 2H, 2H-perfluorododecan-1-ol (10:2 FTOH; CAS No. 865-86-1). Developed methods were evaluated by instrument detection limits (IDLs), quality assurance checks of target standards purchased from different vendors, TD sorbent tube stability and breakthrough, and standard solution storage stability. The TD-GC-MS/MS method was utilized to measure FTOH emissions from consumer products in micro-scale chambers to determine their emission parameters.
2. Experimental
2.1. Chemicals and standards
4:2 FTOH (97.0%), 6:2 FTOH (98.5%), and 8:2 FTOH (97.7%) were obtained from Sigma-Aldrich, Inc. (St. Louis, MO, USA). 10:2 FTOH (97.0%) was obtained from Apollo Scientific Ltd. (Stockport, United Kingdom). Certified solutions of 4:2 FTOH, 6:2 FTOH, 8:2 FTOH, 10:2 FTOH, 2-perfluorooctyl-[1,1-2H2]-[1,2-13C2]-ethanol (8:2 FTOH [M+4]; CAS No. 872398-73-7), and 2-perfluorodecyl-[1,1-2H2]-[1,2-13C2]-ethanol (10:2 FTOH [M+4]; CAS No. 872398-74-8) in methanol (50.0 ± 2.5 μg/mL) were obtained from Wellington Laboratories Inc. (Guelph, ON, Canada). 8:2 FTOH [M+4] was used as a recovery check standard (RCS) and 10:2 FTOH [M+4] was used as an internal standard (IS). Methanol (CAS No. 67-56-1; HPLC grade ≥99.9%) was obtained from Fisher Scientific (Waltham, MA, USA).
2.2. Thermal desorption-gas chromatography-tandem mass spectrometry analysis
TD sorbent tube samples generated for this research were analyzed by TD-GC-MS/MS.
2.2.1. TD-GC-MS/MS standard preparation
Stock solutions of individual FTOH standards and the IS 10:2 FTOH [M+4] were prepared in methanol and stored in Corning™ Falcon™ 15 mL conical centrifuge polypropylene (PP) tubes (Fisher Scientific). Calibration standards containing all four FTOHs were prepared in Nalgene™ 4 mL polypropylene copolymer (PPCO) vials (Fisher Scientific) at the following concentrations: 0.125, 0.25, 0.5, 5.0, 12.5, and 50.0 μg/mL. The IS for calibration and sample analysis was prepared in a separate 4 mL PPCO vial at a concentration of 5.0 μg/mL. Standard vials were stored in a refrigerator (4 °C) until needed.
2.2.2. TD tube standard preparation
Pre-conditioned CAMSCO SilcoNert™ stainless steel tubes (0.25 in × 3.5 in; PFAS sorbent) (CAMSCO, Houston, TX, USA) and pre-conditioned Markes SilcoNert™ stainless steel tubes (0.25 in × 3.5 in; Universal sorbent) (Markes International, Inc., Sacramento, CA, USA) were obtained for TD analysis.
Two μL of calibration standard and IS were spiked and allowed to disperse for 2 min separately with a 10 μL syringe onto pre-conditioned TD tubes using a Markes Calibration Solution Loading Rig (CSLR) at 100 ± 5 mL/min. The tube was capped with a GERSTEL Transport Adapter (GERSTEL, Inc., Linthicum, MD, USA) for analysis or capped with Swagelok® 0.25-inch brass compression caps (PTFE ferrule) (Swagelok Company, Solon, OH, USA) for freezer storage (−20 °C). A calibration curve spiked onto tubes consisted of IS (10.0 ng/tube) and each FTOH at the following concentrations: 0.25, 0.5, 1.0, 10.0, 25.0, and 100.0 ng/tube.
2.2.3. TD-GC-MS/MS instrumentation and analytical method
TD analysis was performed with a GERSTEL Thermal Desorber TD 3.5+ system with the GERSTEL MultiPurpose Sampler (MPS) installed on an Agilent 8890–7000D GC-MS/MS. The GERSTEL Cooled Injected System (CIS) contained a GERSTEL single taper liner packed with silanized glass wool, deactivated (2 mm ID). The TD 3.5+ system operated in splitless mode with the standby temperature set at 50 °C and the transfer temperature set at 320 °C. TD tubes were desorbed with the following temperature program: 50 °C for 0.01 min, 300 °C/min to 300 °C, and 300 °C for 8 min. Desorbed gases were cryo-focused in the CIS at −70 °C by low-pressure liquid nitrogen and then vaporized for on-column injection in the GC inlet with the following temperature program: −70 °C for 0.01 min, 12 °C/s to 280 °C, and 280 °C for 3 min.
Helium was used as the GC carrier gas at 1.2 mL/min. The GC inlet operated in solvent vent mode at 40 °C with the purge flow to split vent at 60 mL/min, the vent flow at 48 mL/min, the vent pressure at 9 psi, and the septum purge flow at 3 mL/min. The split ratio of 50:1 was calculated by dividing the purge flow to split vent by the carrier gas flow. Chromatographic separations were carried out using an Agilent J&W DB-FFAP column (0.25 μm df, 30 m × 0.25 mm ID) with the following GC oven conditions: 40 °C for 2 min, 15 °C/min to 130 °C, 25 °C/min to 240 °C, and 240 °C for 6 min with a total run time of 18.4 min. The MS interface temperature was set at 240 °C.
The Agilent 7000D MS/MS operated in electron impact (EI) mode at 70 electron volts (eV) with a source temperature of 200 °C and quadrupole temperatures of 180 °C. Nitrogen was used as the collision gas at 1.5 mL/min and helium was used as the quench gas at 4.0 mL/min. The solvent delay was 4.5 min. For quantification, MRM acquisition mode was used with one quantifier precursor-to-product mass transition and two qualifier precursor-to-product mass transitions for each target compound. Mass transitions for MRM acquisition were manually selected and optimized. First, FTOH standards were analyzed in full scan mode. The ions with highest absolute signal abundance in full scan mode (~5 – 10 for each analyte) were run in product scan mode at collision energies (CE) 5, 10, 15, and 20 eV. The precursor-to-product mass transitions with the highest absolute signal abundance and lowest background noise (~15 – 20 mass transitions for each analyte) were selected to run in MRM mode. Three mass transitions per analyte were chosen based on signal abundance, background noise, and commonality across target analytes. When mass transition signal abundance was similar between two CE’s, the lower CE was preferred to reduce background noise. Data analysis was performed using Agilent MassHunter Workstation Quantitative Analysis software (version 10.0.707.0).
Due to instrument availability, additional TD tube analysis was performed with a Markes TD-100 automated thermal desorber coupled to an Agilent 7890A-5975C gas chromatograph-single quadrupole mass spectrometer (GC-MS). The details for TD, GC, and MS parameters are in Supplemental S.1.
2.3. Gas chromatography-tandem mass spectrometry liquid sample analysis
Liquid samples generated for this research were analyzed by GC-MS/MS with a liquid injection autosampler.
2.3.1. GC-MS/MS standard preparation
The stock FTOH and IS solutions described in Section 2.2.1 were used to prepare standards for liquid sample analysis in Corning™ Falcon™ 15 mL conical centrifuge PP tubes and aliquoted into Agilent 2 mL screw top PP vials. Additionally, a stock solution of the RCS 8:2 FTOH [M+4] was prepared in methanol and stored in a Corning™ Falcon™ 15 mL conical centrifuge PP tube. Prepared calibration standards included IS (50.0 ng/mL) and each FTOH and the RCS at the following concentrations: 5.0, 10.0, 25.0, 50.0, 100.0, and 200.0 ng/mL. Standard vials were stored in a refrigerator (4 °C) until needed.
2.3.2. GC-MS/MS instrumentation and analytical method
Liquid samples were analyzed using an Agilent 7890A-7000 GC-MS/MS. Helium was used as the GC carrier gas at 1.2 mL/min. The GC inlet operated in pulsed splitless mode (25 psi) at 200 °C with a purge flow of 50.0 mL/min after 0.5 min. The septum purge flow was set at 3 mL/min and the gas saver was set at 20 mL/min after 3 min. The inlet contained an Agilent Ultra Inert splitless single taper liner packed with glass wool (4 mm ID). The GC column, GC oven, MS interface, and MS/MS conditions were unchanged from the TD tube analysis (Section 2.2.3). The quantifier and qualifier MRM mass transitions were modified to accommodate for lower sensitivity with the Agilent 7000 MS/MS (see Supplemental S.2).
Additional liquid sample analysis was performed with the Agilent 8890–7000D GC-MS/MS before it was converted to a TD-GC-MS/MS system when the Agilent 7890A-7000 GC-MS/MS was not available. Refer to Supplemental S.3 for GC-MS/MS conditions.
2.4. Instrument detection limit
The IDLs for the TD-GC-MS/MS and the liquid injection GC-MS/MS methods were determined by analyzing the lowest calibration levels (0.25 ng/tube for TD, 5.0 ng/mL for liquid) seven times each. The standard deviation of the seven calculated concentrations was multiplied by three to obtain the IDL for each analytical method [30].
2.5. TD tube storage stability
The stability of FTOHs spiked onto TD tubes was investigated over a period of 28 days. CAMSCO PFAS and Markes Universal TD tubes were spiked in duplicate with 2 μL of 200.0 μg/mL FTOH standard (400.0 ng/tube). The spiked TD tubes were sealed with Swagelok® 0.25-inch brass compression caps and stored in individual Tedlar bags at 4 °C in a refrigerator along with a field blank of each tube type for each day of sampling. TD tubes were removed from the refrigerator on days 1, 4, 7, 10, 14, 21, and 28 and allowed to equilibrate to room temperature for 1 h. The TD tubes were spiked with 2 μL of IS (50.0 ng/tube) and analyzed with the Markes TD-100-Agilent 7890A-5975C TD-GC-MS system.
2.6. TD tube breakthrough
The retention of FTOHs spiked onto TD tubes was investigated by breakthrough tests. CAMSCO PFAS or Markes Universal TD tubes were coupled in-series with a Swagelok® stainless steel nut on the Markes CSLR with a nitrogen flow of 100 ± 5 mL/min. FTOH standard was spiked (400.0 ng/tube) onto the coupled TD tubes and tubes were purged for 5, 10, 30, 50, 80, 100, 150, and 200 min. Each breakthrough test was performed in triplicate. The TD tubes were then individually spiked with 2 μL of IS (50.0 ng/tube) and analyzed with the Markes TD-100-Agilent 7890A-5975C TD-GC-MS system.
2.7. Liquid storage stability
The stability of FTOH standards in methanol solution was investigated in PPCO vials at different temperatures. Mixtures of all four FTOHs were prepared in methanol at 10.0 ng/mL and 100.0 ng/mL (with IS at 50.0 ng/mL). Two mL of each concentration level was aliquoted in duplicate into 4 mL PPCO vials and stored at 4 °C in a refrigerator and at 23 °C in an incubator. Additionally, one field blank of methanol (2 mL) was stored at each temperature condition for each day of sampling. Vials were removed on days 1, 4, 8, 11, 14, 21, and 28 and analyzed with the Agilent 8890–7000D GC-MS/MS.
2.8. Consumer product extractions
Consumer products were extracted in duplicate by sonication in methanol and analyzed with the Agilent 7890A-7000 GC-MS/MS to measure FTOH levels. The products selected to confirm the developed GC-MS/MS and TD-GC-MS/MS methods were obtained from a previous project [5]. The products were categorized as mattress pad 1 (USA), mattress pad 2 (China), and stone cleaner/resealer 1 (USA).
For each product extraction, 100 μL of a liquid product was added to a tared 15 mL PP centrifuge tube and the mass was recorded. To the tube, 1880 μL of methanol and 20 μL of RCS (50.0 ng/mL) were added. Approximately 50 mg of a solid product was cut into uniform pieces and added to a 15 mL PP centrifuge tube. To the tube, 1980 μL of methanol and 20 μL of RCS (50.0 ng/mL) were added. Tubes were vortexed, sonicated for 10 min, and then centrifuged at 3000 rpm for 2 min. For solid product extractions, if particles were visible, the tubes were centrifuged for an additional 2 min at 5000 rpm. If particulates were visible in the supernatant, the sample was filtered with a 0.20 μm syringe filter. After extraction and cleanup, the supernatant (990 μL) was then combined with 10 μL of IS (50.0 ng/mL) in a 2 mL PP vial and analyzed with the Agilent 7890A-7000 GC-MS/MS. The extraction efficiency was evaluated by the % recovery of the RCS, which was determined by the concentration of RCS measured in samples divided by the average concentration of RCS measured in standards prepared in triplicate.
2.9. Consumer product emissions
Consumer product emissions tests were conducted using a Markes Micro-Scale Chamber/Thermal Extractor™ (μ-CTE™) system that was set at 25 °C, 34% relative humidity, and approximately 100 mL/min of clean air from a clean air generation system.
A 64 mm diameter circle was cut from each of the two mattress pad products and placed in individual 114 mL micro-scale chamber cells. Two aliquots of 1.2-gram stone cleaner/resealer product were spiked into two chamber cells, respectively. The bottom of each chamber cell was covered with the test products. The two liquid product tests served as a duplicate for quality assurance and quality control purpose. The micro-scale chamber tests conformed to American Society of Testing and Materials (ASTM) D7706 [31]. Concentrations of FTOHs in the source materials were determined prior to micro-scale chamber tests as described in the section above. TD tube samples were collected from the micro-scale chambers with sampling durations up to 90 minutes each at approximately 102 mL/min. Samples were collected for 125 h for the mattress pad tests and for 28 h for the liquid stone cleaner/resealer product. Background samples were collected prior to placing the test materials in the chambers.
2.10. Quality assurance and quality control
A quality assurance project plan (QAPP) was prepared according to EPA requirements before the project was started. The acceptance criteria for the calibration required a coefficient of determination (r2) of 0.99 or greater. The certified solutions purchased from Wellington Laboratories of the four target FTOHs were used for an internal audit program (IAP). IAP standards were prepared by someone other than the person who prepared the calibration standards and were submitted without concentration information to the analyst who conducted the calibrations. The IAP standards were analyzed after each calibration as a measurement of calibration verification with the acceptance criteria for the % recovery (calculated IAP concentration from the calibration/known IAP concentration) being 100 ± 25% and % relative standard deviation (RSD) of triplicate analysis being ± 25%. Daily calibration check (DCC) standards from the midpoint of the calibration curve were prepared and analyzed prior to sample analysis to evaluate instrument performance. Analytical results of a sample batch were considered acceptable if the % recovery of the DCC was 100 ± 25%. Methanol blank and IS control samples were prepared and analyzed to evaluate material contamination and TD-GC-MS/MS carryover and background [32].
Following analysis, TD tubes were reconditioned to remove contaminants. Reconditioned TD tubes were checked for residual contamination prior to reuse. One tube for every batch of ten reconditioned tubes was spiked with IS and analyzed by TD-GC-MS or TD-GC-MS/MS. If the summed mass of FTOHs measured above 0.25 ng/tube for TD-GC-MS/MS analysis or above 5 ng/tube for TD-GC-MS analysis, the batch was rejected, and the tubes were reconditioned.
3. Results and Discussion
3.1. TD-GC-MS/MS method performance
Table 1 lists the MRM parameters used for analysis of FTOHs by TD-GC-MS/MS. The chromatograms of the mass transitions are illustrated in Fig. 1. The selected mass transitions were mostly consistent with previously published methods for analysis of FTOHs in liquid solutions by GC-MS/MS [23,33].
Table 1.
MRM mode parameters for the analysis of FTOHs with the GERSTEL TD 3.5+ coupled to the Agilent 8890–7000D GC-MS/MS system. Peak resolution was set to “wide” for each mass transition.
| TS | Dwell | Quantifier | Qualifier 1 | Qualifier 2 | ||||
|---|---|---|---|---|---|---|---|---|
| Analyte | min | ms | m/z | eV | m/z | eV | m/z | eV |
|
| ||||||||
| 4:2 FTOH | 4.5 | 50 | 244 → 127 | 10 | 95 → 69 | 15 | 127 → 77 | 15 |
| 6:2 FTOH | 6.0 | 50 | 344 → 127 | 10 | 95 → 69 | 15 | 127 → 77 | 15 |
| 8:2 FTOH [M+4] | 6.7 | 25 | 129 → 79 | 20 | 415 → 96 | 10 | 448 → 129 | 5 |
| 8:2 FTOH | 6.7 | 25 | 444 → 127 | 10 | 95 → 69 | 15 | 127 → 77 | 15 |
| 10:2 FTOH [M+4] | 7.5 | 25 | 129 → 79 | 20 | 515 → 96 | 15 | 548 → 129 | 5 |
| 10:2 FTOH | 7.5 | 25 | 544 → 127 | 10 | 95 → 69 | 20 | 127 → 77 | 20 |
TS = time segment for MRM scan; min = minutes; ms = milliseconds; m/z = mass-to-charge ratio; eV = collision energy electron volts.
Fig. 1.
Total ion chromatogram (TIC) of four FTOHs and the IS acquired by MRM mode on the Agilent 8890–7000D GC-MS/MS. Three chromatographic traces for each compound comprise of the quantifier mass transition and two qualifier mass transitions. (* 10:2 FTOH [M+4] qualifier mass transitions m/z 515 → 96 and m/z 548 → 129).
The calibration of the TD-GC-MS/MS method is summarized in Table 2. The RSDs of the relative response factors (RRF) ranged from 7.9 – 13.3%. The IAP standards all met acceptance criteria of ± 25% recovery with a range of 83.9 – 85.6% of the known concentrations.
Table 2.
Calibration curve statistics for TD-GC–MS/MS analysis of the four target FTOHs ( n = 6; N = 18; range = 0.25 −100.0 ng/tube) and the RCS ( n = 5; N = 15; range = 0.25 −4.0 ng/tube), and GC–MS/MS analysis of the four target FTOHs and the RCS ( n = 6; N = 18; range = 5.0 −200.0 ng/mL).
| Calibration | IDL | IAP | ||
|---|---|---|---|---|
| TD tubes | RRF | RSD | ng/tube | recovery |
|
| ||||
| 4:2 FTOH | 0.73 | 8.9% | 0.09 | 84.1% |
| 6:2 FTOH | 0.56 | 7.9% | 0.09 | 85.6% |
| 8:2 FTOH [M+4] | 0.64 | 11.6% | 0.07 | NA |
| 8:2 FTOH | 0.28 | 9.6% | 0.07 | 84.6% |
| 10:2 FTOH | 0.13 | 13.3% | 0.07 | 83.9% |
|
| ||||
| Calibration | IDL | IAP | ||
| Liquid samples | RRF | RSD | ng/mL | recovery |
|
| ||||
| 4:2 FTOH | 2.17 | 2.8% | 0.65 | 106.6% |
| 6:2 FTOH | 3.15 | 2.7% | 0.53 | 104.8% |
| 8:2 FTOH [M+4] | 1.16 | 4.2% | 0.39 | NA |
| 8:2 FTOH | 4.20 | 2.6% | 0.67 | 100.6% |
| 10:2 FTOH | 1.45 | 3.4% | 1.10 | 97.4% |
n = calibration levels; N = total number of injections; RRF = average relative response factor of the calibration curve standards; RSD = relative standard deviation of the relative response factors; IDL = instrument detection limit; IAP = internal audit program standards; recovery = calculated concentrations of the IAP standards as a percentage of the calibration standard concentrations; NA = not applicable.
3.2. GC-MS/MS method performance
Three mass transitions were acquired in MRM mode by the Agilent 7890A-7000 GC-MS/MS (an older model of GC-MS/MS) for quantification of FTOH analytes in methanol solutions (Table S.2). Due to lower sensitivity of the Agilent 7000 MS/MS, different quantifier mass transitions were selected to maintain the calibration range analyzed with the Agilent 8890–7000D GC-MS/MS (Table S.3a). The Agilent 7890A-7000 GC-MS/MS calibration results are summarized in Table 2 and the Agilent 8890–7000D GC-MS/MS calibration results are summarized in Table S.3b. The RSDs and the IAP recoveries were both higher for TD tube calibration due to variability of spiking tubes and TD desorption. Refer to Supplemental S.2 and S.3 for additional information on the calibration method performance of the Agilent 7890–7000 GC-MS/MS and the Agilent 8890–7000D GC-MS/MS.
3.3. TD tube stability tests
Stability of FTOHs spiked onto TD tubes at a high concentration (~ 400.0 ng/tube) was tested. The FTOH concentrations spiked onto TD tubes were compared to the concentrations spiked onto TD tubes when the stability test samples were prepared (denoted as day 0). The results of the TD tube stability are shown in Fig. 2. Neither TD tube type exhibited significant loss of FTOH compounds over a period of 28 days. RSDs ranged from 6.4 – 7.7% for FTOH concentrations measured in CAMSCO PFAS tubes and ranged from 3.1 – 3.7% for FTOH concentrations measured in Markes Universal tubes (Table S.4 and Tables S.5a & 5b).
Fig. 2.
Time-series concentration profiles of FTOHs spiked onto CAMSCO PFAS (left) and Markes Universal (right) TD tubes (400.0 ng/tube) stored in a 4 °C refrigerator over a period of 28 days. In the left side figure, the 0-, 1-, 3-, 7-, and 10-day TD tubes were reprepared on a different date from the date 14-, 22-, and 28-day TD tubes were prepared due to instrument recalibration. The %RSD of each data point are presented in Tables S.5a (CAMSCO) and S.5b (Markes).
3.4. TD tube breakthrough tests
Breakthrough is confirmed if the loss of analyte is higher than 5% of the analyte entering the second tube [20–21]. The breakthrough tests indicated the PFAS sorbent in the CAMSCO SilcoNert™ stainless steel tubes and the Universal sorbent in the Markes SilcoNert™ stainless steel tubes had high retention of FTOHs for sampling durations of 5 – 200 min at a nitrogen flow rate of 100 ± 5 mL/min. FTOHs were not measured above the lowest calibration standard (~5.0 ng/tube) in any of the second tubes of the breakthrough tests. The breakthrough percentage was calculated by dividing the FTOH concentration in the second tube by the FTOH concentration in the first tube. All breakthrough percentages were less than 1% for sampling volumes of 0.5 – 20.0 L (Table 3). Additionally, FTOHs were not detected in the second tube in 21 of the 64 tests. The stability and breakthrough tests indicated both CAMSCO PFAS and Markes Universal TD tubes were suitable for FTOH collection and analysis.
Table 3.
Breakthrough experiments with FTOHs spiked onto CAMSCO PFAS or Markes Universal TD tubes connected in series. Each test was performed in triplicate with CAMSCO PFAS and Markes Universal tubes.
| CAMSCO PFAS tubes | Markes Universal tubes | |||||||
|---|---|---|---|---|---|---|---|---|
| FTOH | 4:2 | 6:2 | 8:2 | 10:2 | 4:2 | 6:2 | 8:2 | 10:2 |
|
|
|
|||||||
| Volume (L) | ||||||||
| 0.5 | NAa | NA | 0.09% | NA | NA | 0.04% | 0.09% | NA |
| 1.0 | NA | 0.07% | 0.16% | 0.24% | 0.04% | 0.05% | 0.08% | NA |
| 3.0 | NA | 0.10% | 0.24% | 0.38% | NA | NA | 0.17% | NA |
| 5.0 | NA | NA | 0.38% | 0.51% | 0.12% | NA | 0.28% | 0.44% |
| 8.0 | NA | 0.17% | 0.33% | 0.33% | 0.04% | 0.06% | 0.17% | 0.36% |
| 10.0 | NA | 0.19% | 0.18% | 0.32% | 0.16% | 0.20% | 0.31% | 0.39% |
| 15.0 | NA | NA | NA | 0.36% | 0.18% | 0.13% | 0.22% | 0.37% |
| 20.0 | NA | NA | 0.24% | 0.47% | 0.23% | 0.20% | 0.44% | 0.68% |
Not applicable denotes when an FTOH was not detected in the second tube connected in series.
3.5. Liquid storage stability tests
Stability of FTOH standards at concentrations of 10.0 and 100.0 ng/mL in methanol were tested in PPCO vials stored at temperatures of 4 °C and 23 °C for 1 – 28 days. The FTOH concentrations were compared to the concentrations measured in the freshly prepared standards (denoted as day 0). The results of the liquid storage stability tests are shown in Fig. 3. Neither temperature condition exhibited significant loss of FTOH compounds over a period of 28 days. RSDs ranged from 4.3 – 6.2% for FTOH concentrations in PPCO vials stored at 4 °C and ranged from 6.6 – 8.4% for FTOH concentrations in PPCO vials stored at 23 °C (Tables S.6 & S.7a–d). These results are consistent with previous studies on stability of PFAS stored in different materials at different temperatures [32,34].
Fig. 3.
Time-series concentration profiles of FTOHs in methanol solutions stored in PPCO vials at following conditions: A) 10 ng/mL at 23 °C; B) 100 ng/mL at 23 °C; C) 10 ng/mL at 4 °C; and D) 100 ng/mL at 4 °C. The %RSD of each data point are presented in Tables S.7a to S.7d.
3.6. Consumer product extractions
The FTOH concentrations in two mattress pads and one stone cleaner/sealer used for the micro-scale chamber emission tests are reported in Table 4. The solvent extraction efficiency evaluated by the recovery of spiked 8:2 FTOH [M+4] ranged from 80 – 99% (Table S.8). 4:2 FTOH was not detected in any of the products, and 6:2 FTOH was not detected in either of the mattress pads. Among these three products, the stone cleaner/sealer contained the highest levels of FTOHs with concentrations exceeding 10.0 μg/g of 6:2 FTOH, 6.0 μg/g of 8:2 FTOH, and 700.0 ng/g of 10:2 FTOH. The two mattress pad products contained 642 – 753 ng/g of 8:2 FTOH and 232 – 364 ng/g of 10:2 FTOH. These products, purchased in 2011 and 2013, were used to evaluate the analytical methods and do not reflect current market trends.
Table 4.
FTOH emission parameters obtained by model fit for micro-scale chamber emission testing of consumer products.
| Consumer Product | Avg Conc. | Emission Model | |||
|---|---|---|---|---|---|
| ID-Description | ng/g (N = 2) | k(/h) | EF0 (mg/m2/h) | R2 | |
|
|
|
||||
| 6:2 FTOH | |||||
| 621-Stone cleaner/sealer 1a | 1.24E4 ± 21.6 | 1.03 | 5.89E-02 | 0.9987 | |
| 621-Stone cleaner/sealer 1b | 1.24E4 ± 21.6 | 0.97 | 5.09E-02 | 0.9996 | |
|
|
|
||||
| 8:2 FTOH | |||||
| 593-Mattress pad 1 | 6.42E2 ± 18.5 | 0.55 | 7.74E-03 | 0.9972 | |
| 617-Mattress pad 2 | 7.53E2 ± 2.0 | 0.03 | 1.19E-04 | 0.9742 | |
| 621-Stone cleaner/sealer 1a | 6.04E3 ± 15.8 | 0.64 | 2.24E-01 | 0.9977 | |
| 621-Stone cleaner/sealer 1b | 6.04E3± 15.8 | 0.70 | 2.52E-01 | 0.9998 | |
|
|
|
||||
| 10:2 FTOH | |||||
| 593-Mattress pad 1 | 2.32E2 ± 12.4 | 0.10 | 6.58E-03 | 0.9944 | |
| 617-Mattress pad 2 | 3.64E2 ± 6.8 | 0.07 | 4.43E-04 | 0.8912 | |
| 621-Stone cleaner/sealer 1a | 7.25E2 ± 6.4 | 0.19 | 4.89E-02 | 0.9898 | |
| 621-Stone cleaner/sealer 1b | 7.25E2 ± 6.4 | 0.22 | 5.59E-02 | 0.9643 | |
Avg Conc. = average concentration (ng/g) and standard deviation of extracted FTOHs in consumer products; k(/h) = decay rate constant; EF0 = initial emission factor; R2 = goodness-of-fit statistic for least-squares regression model
= duplicate tests.
3.7. Consumer product micro-scale chamber emissions
The micro-scale chamber is advantageous for sampling semivolatile organic chemicals emitted from consumer products by minimizing the sink effect to the chamber walls. Emissions of 8:2 and 10:2 FTOHs were determined from the mattress pad products with a relatively slow decay rate (Fig. 4A, 4B). Emissions of 6:2, 8:2, and 10:2 FTOHs were measured from the liquid stone cleaner/sealer product (Fig. 4C, 4D). For the two mattress pad products, 10:2 FTOHs emitted at higher concentrations than 8:2 FTOHs even though its vapor pressure is lower than that of 8:2 FTOH [1]. The liquid product rapidly evaporated and the chambers were dried out after 28 h. The emissive concentrations of FTOHs are in the order of 8:2 FTOH > 10:2 FTOH > 6:2 FTOH, which is also in contrast to their order in vapor pressures. The observation implies that FTOH emission mechanisms are different from other volatile and semivolatile chemical emissions from consumer products [35]. To explain this point, future studies are needed. Source emissions are characterized by physicochemical property parameters, such as emission factor and emission rate constant, which are not affected by the test material size, loading factor, air exchange rate, etc. These parameters can be used to predict the gas-phase concentration or emission rate under various environmental conditions for further exposure assessment. The emission data collected was fitted by the least-square method to the first order decay model using the SCIENTIST® program (Micromath Scientific Software) to obtain the initial emission factor (EF0) and the first order decay rate constant (k) based on ASTM D5116 [36]. The equations used for the first-order decay model are described in Supplemental S.5. The data from the model fitting are presented in Table 4. The emission pattern and the emission parameters obtained from this work will provide information and support inhalation exposure assessment by modelers.
Fig. 4.
Time-series concentration profiles of FTOH emissions from consumer products collected from micro-scale chambers containing the following products: A) mattress pad 1; B) mattress pad 2; C) stone cleaner/resealer 1; and D) stone cleaner/resealer 1 (duplicate test of C).
4. Conclusions
In this study we presented optimized analytical conditions and calibration performance for the TD-GC-MS/MS and GC-MS/MS methods. The TD tube storage stability and breakthrough, and the liquid solution stability were investigated. The methods have been applied for characterization of FTOH emissions from solid and liquid consumer products using micro-scale chambers. Analytical methods for TD tube and liquid samples were sensitive and specific for all four FTOHs of interest. The emission factor and first order decay rate constants were obtained. To the author’s best knowledge, this is the first application of TD-GC-MS/MS method for determining emission parameters from consumer products. The emission parameter data generated from this work is also the first in the literature and could be used as input parameters for PFAS exposure assessments. We note that other neutral PFAS like fluorotelomer acrylates were not included in this method development due to resource constraints. Additionally, only three consumer products were tested and reported under laboratory conditions in this work. Realistic indoor sampling conditions may affect the sensitivity of the method due to higher background and may lead to increased breakthrough due to more competition for sorption sites. Consumer product studies on their sources, emissions, and fate and transport in the indoor environment are in progress. Our research demonstrated that these methods prove suitable for quantification of FTOHs in chamber air and could be applied to the analysis of indoor air and ambient air. The TD-GC/MS/MS method development and implementation of materials and methods to micro-scale chamber testing of consumer products containing FTOHs will translate to the analysis of other PFAS found in the indoor environment. In the future, we will aim to develop a consensus measurement TD-GC-MS/MS method to fill data gaps in PFAS exposure assessments [35].
Supplementary Material
Acknowledgements
We would like to thank M. Ariel Wallace and Matthew S. Clifton from the U.S. EPA for assistance with analytical method development. We would also like to thank Edgar Folk IV from Jacobs Solutions Inc. for general lab support. There is a Cooperative Research and Development Agreement (CRADA) # 1396–21 between U.S. EPA and GERSTEL Inc. for this research.
Footnotes
Disclaimer
This manuscript has been reviewed in accordance with U.S. EPA policy and approved for publication. The views expressed are those of the author and do not necessarily represent the views and policies of the agency. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
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