ASTM D7968-23

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D7968 − 23
Standard Test Method for
Determination of Polyfluorinated Compounds in Soil by
Liquid Chromatography Tandem Mass Spectrometry (LC/
MS/MS)
This standard is issued under the fixed designation D7968; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope reporting limit are estimated concentrations and are not re-
ported following this test method. In most cases, the reporting
1.1 This procedure covers the determination of selected
limit is calculated from the concentration of the Level 1
polyfluorinated alkyl substances (PFAS) in a soil matrix using
calibration standard as shown in Table 2 for the PFAS after
solvent extraction, filtration, followed by liquid chromatogra-
taking into account a 2 g sample weight and a final extract
phy (LC) and detection with tandem mass spectrometry (MS/
volume of 10 mL, 50 % water/50 % MeOH with 0.1 % acetic
MS). These analytes are qualitatively and quantitatively deter-
acid. The final extract volume is assumed to be 10 mL because
mined by this method. This method adheres to multiple
10 mL of 50 % water/50 % MeOH with 0.1 % acetic acid was
reaction monitoring (MRM) mass spectrometry. This proce-
added to each soil sample and only the liquid layer after
dure utilizes a quick extraction and is not intended to generate
extraction is filtered, leaving the solid and any residual solvent
an exhaustive accounting of the content of PFAS in difficult
behind. It is raised above the Level 1 calibration concentration
soil matrices. An exhaustive extraction procedure for PFAS,
2 for PFOS, PFHxA, FHEA, and FOEA; these compounds can
such as published by Washington et al., for difficult matrices
be identified at the Level 1 concentration but the standard
should be considered when analyzing PFAS. The approach
deviation among replicates at this lower spike level resulted in
from this standard was utilized to screen laboratory coats
a higher reporting limit.
(textiles) to identify if PFAS would be leached from the
1.4 This standard does not purport to address all of the
materials.
safety concerns, if any, associated with its use. It is the
1.2 Units—The values stated in SI units are to be regarded
responsibility of the user of this standard to establish appro-
as standard. No other units of measurement are included in this
priate safety, health, and environmental practices and deter-
standard.
mine the applicability of regulatory limitations prior to use.
3 4
1.3 The method of detection limit and reporting range for
1.5 This international standard was developed in accor-
the target analytes are listed in Table 1.
dance with internationally recognized principles on standard-
1.3.1 The reporting limit in this test method is the minimum
ization established in the Decision on Principles for the
value below which data are documented as non-detects. Ana-
Development of International Standards, Guides and Recom-
lyte detections between the method detection limit and the
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2. Referenced Documents
This test method is under the jurisdiction of ASTM Committee D34 on Waste
Management and is the direct responsibility of Subcommittee D34.01.06 on
2.1 ASTM Standards:
Analytical Methods.
D1193 Specification for Reagent Water
Current edition approved Nov. 1, 2023. Published November 2023. Originally
D2777 Practice for Determination of Precision and Bias of
approved in 2014. Last previous edition approved in 2017 as D7968 – 17a. DOI:
10.1520/D7968-23. Applicable Test Methods of Committee D19 on Water
Washington, J. W., Naile, J. E., Jenkins, T. M., and Lynch, D. G., “Character-
D5847 Practice for Writing Quality Control Specifications
izing Fluorotelomer and Polyfluoroalkyl Substances in New and Aged
for Standard Test Methods for Water Analysis
Fluorotelomer-Based Polymers for Degradation Studies with GC/MS and LC/MS/
E2554 Practice for Estimating and Monitoring the Uncer-
MS,” Environmental Science and Technology, Vol 48, 2014, pp. 5762–5769.
The MDL is determined following the Code of Federal Regulations, 40 CFR
tainty of Test Results of a Test Method Using Control
Part 136, Appendix B utilizing solvent extraction of soil. A 2 g sample of Ottawa
Chart Techniques
sand was utilized. A detailed process determining the MDL is explained in the
reference and is beyond the scope of this standard to be explained here.
4 5
Reporting range concentration is calculated from Table 2 concentrations For referenced ASTM standards, visit the ASTM website, www.astm.org, or
assuming a 30 μL injection of the Level 1 calibration standard for the PFAS, and the contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
highest level calibration standard with a 10 mL final extract volume of a 2 g soil Standards volume information, refer to the standard’s Document Summary page on
sample. Volume variations will change the reporting limit and ranges. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7968 − 23
A
TABLE 1 Method Detection Limit and Reporting Range
3.2.18 PFecHS—Decaluoro-4-
MDL Reporting Limit
(pentafluoroethyl)cyclohexanesulfonate
Analyte
(ng/kg) (ng/kg)
3.2.19 PFAC—Perfluoroalkyl Carboxylic Acid
PFTreA 6.76 25–1000
PFTriA 5.26 25–1000
3.2.20 PFBA—Perfluorobutanoate
PFDoA 3.56 25–1000
PFUnA 2.45 25–1000
3.2.21 PFPeA—Perfluoropentanoate
PFDA 5.54 25–1000
PFOS 18.83 50–1000 3.2.22 PFHxA—Perfluorohexanoate
PFNA 2.82 25–1000
3.2.23 PFHpA—Perfluoroheptanoate
PFecHS 2.41 25–1000
PFOA 6.24 25–1000
3.2.24 PFOA—Perfluorooctanoate
PFHxS 7.75 25–1000
PFHpA 5.80 25–1000 3.2.25 PFNA—Perfluorononanoate
PFHxA 15.44 50–1000
3.2.26 PFDA—Perfluorodecanoate
PFBS 6.49 25–1000
PFPeA 20.93 125–5000
3.2.27 PFUnA—Perfluoroundecanoate
PFBA 22.01 125–5000
FHEA 199.04 600–20 000 3.2.28 PFTriA—Perfluorotridecanoate
FOEA 258.37 750–20 000
3.2.29 PFTreA—Perfluorotetradecanoate
FDEA 137.46 500–20 000
FOUEA 4.85 25–1000
3.2.30 FTAs and FTUAs—Fluorotelomer and Unsaturated
FhpPa 5.09 25–1000
Fluorotelomer Acids
FHUEA 3.50 25–1000
A
Abbreviations are defined in 3.2. 3.2.31 FHpPA—3-perfluoropheptyl propanoic acid
3.2.32 FOUEA—2H-perfluoro-2-decenoic acid
3.2.33 FDEA—2-perfluorodecyl ethanoic acid
2.2 Other Documents:
3.2.34 FOEA—2-perfluorooctyl ethanoic acid
EPA SW-846 Test Methods for Evaluating Solid Waste,
Physical/Chemical Methods
3.2.35 FHUEA—2H-perfluoro-2-octenoic acid
40 CFR Part 136 Appendix B Definition and Procedure for
3.2.36 FHEA—2-perfluorohexyl ethanoic acid
the Determination of the Method Detection Limit
3.2.37 MPFAS—Isotopically labeled Perfluoroal-
kylsulfonates
3. Terminology
3.2.38 MPFHxS— O -Perfluorohexylsulfonate
3.1 Definitions: 2
3.1.1 reporting limit, RL, n—the minimum concentration
3.2.39 MPFOS— C -Perfluorooctylsulfonate
below which data are documented as non-detects.
3.2.40 MPFCA—Isotopically labeled Perfluoroalkylcar-
3.2 Abbreviations:
boxylates
3.2.1 CCC—Continuing Calibration Check
3.2.41 MPFBA— C -Perfluorobutanoate
3.2.2 IC—Initial Calibration
3.2.42 MPFHxA— C -Perfluorohexanoate
3.2.3 ppt—parts per trillion, ng/kg or ng/L
3.2.43 MPFOA— C -Perfluorooctanoate
3.2.4 LC—Liquid Chromatography
3.2.44 MPFNA— C -Perfluorononanoate
3.2.5 LCS/LCSD—Laboratory Control Sample/Laboratory
3.2.45 MPFDA— C -Perfluorodecanoate
Control Sample Duplicate
3.2.46 MPFUnA— C -Perfluoroundecanoate
3.2.6 MDL—Method Detection Limit
3.2.47 MPFDoA— C -Perfluorodecanoate
3.2.7 MeOH—Methanol
3.2.48 QA—Quality Assurance
–3
3.2.8 mM—millimolar, 1 × 10 moles/L
3.2.49 QC—Quality Control
3.2.9 MRM—Multiple Reaction Monitoring
3.2.50 RL—Reporting Limit
3.2.10 MS/MSD—Matrix Spike/Matrix Spike Duplicate
3.2.51 RLCS—Reporting Limit Check Sample
3.2.11 NA—Not available
3.2.52 RSD—Relative Standard Deviation
3.2.12 ND—Non-detect
3.2.53 RT—Retention Time
3.2.13 P&A—Precision and Accuracy
3.2.54 SRM—Single Reaction Monitoring
3.2.14 PFAS—Perfluoroalkyl substances
3.2.55 SS—Surrogate Standard
3.2.15 PFBS—Perfluorobutylsulfonate
3.2.56 TC—Target Compound
3.2.16 PFHxS—Perfluorohexylsulfonate
4. Summary of Test Method
3.2.17 PFOS—Perfluorooctylsulfonate
4.1 The operating conditions presented in this test method
have been successfully used in the determination of polyfluo-
Available from National Technical Information Service (NTIS), U.S. Depart-
rinated compounds in soil; however, this test method is
ment of Commerce, 5285 Port Royal Road, Springfield, VA, 22161, http://
www.epa.gov/epawaste/hazard/testmethods/index.htm intended to be performance based and alternative operating
D7968 − 23
TABLE 2 Concentrations of Calibration Standards (ng/L)
Analyte/Surrogate LV1 LV2 LV3 LV4 LV5 LV6 LV7 LV8 LV9
PFPeA, PFBA 25 50 100 200 300 400 500 750 1000
PFTreA, PFTriA, PFDoA, PFUnA, PFDA, PFOS, PFNA, PFHxA, PFHpA, PFBS,
PFechS, PFOA, PFHxS, FOUEA, FHUEA, FHpPA, MPFBS, MPFHxA, MPFUnA, 5 10 20 40 60 80 100 150 200
MPFOA, MPFDA, MPFOS, MPFNA, MPFHxS, MPFBA
FHEA, FOEA, FDEA 100 200 400 800 1200 1600 2000 3000 4000
conditions can be used to perform this method provided data through a polypropylene filter unit. Acetic acid (~50 μL) is
quality objectives are attained. added to all the filtered samples to adjust the pH ~3 to 4 and
then analyzed by LC/MS/MS.
4.2 For PFAS analysis, samples are shipped to the lab on ice
and analyzed within 28 days of collection. A sample (2 g) is 4.3 Most of the PFAS target compounds are identified by
transferred to a polypropylene tube, spiked with surrogates (all comparing the single reaction monitoring (SRM) transition and
samples) and target PFAS (laboratory control and matrix spike its confirmatory SRM transition if correlated to the known
samples). The analytes are tumbled for an hour with 10 mL of standard SRM (Table 3) and quantitated utilizing an external
methanol:water (50:50) under basic condition (pH ~9 to 10 calibration. The surrogates and some PFAS target analytes
adjusted with ~20 μL ammonium hydroxide). The samples are (PFPeA, PFBA, FOUEA, and FHUEA) only utilize one SRM
centrifuged and the extract, leaving the solid behind, is filtered transition due to a less sensitive or non-existent secondary
TABLE 3 Retention Times, SRM Ions, and Analyte-Specific Mass Spectrometer Parameters
Primary/
Primary/ Retention Times
Chemical Cone (V) Collision (eV) MRM Transition Confirmatory SRM
Confirmatory (min)
Area Ratio
Primary 20 13 712.9→668.9
PFTreA 10.63 7.4
Confirmatory 20 30 712.9→169
Primary 25 12 662.9→618.9
PFTriA 10.17 7.4
Confirmatory 25 28 662.9→169
Primary 10 12 612.9→568.9
PFDoA 9.61 8.2
Confirmatory 10 25 612.9→169
Primary 15 10 562.9→519
PFUnA 9.05 7.2
Confirmatory 15 18 562.9→269
Primary 20 10 512.9→468.9
PFDA 8.45 6.5
Confirmatory 20 16 512.9→219
Primary 10 42 498.9→80.1
PFOS 8.78 1.3
Confirmatory 10 40 498.9→99.1
Primary 20 10 462.9→418.9
PFNA 7.78 4.9
Confirmatory 20 16 462.9→219
Primary 10 25 460.9→381
PFecHS 8.1 2.2
Confirmatory 10 25 460.9→99.1
Primary 20 10 412.9→369
PFOA 7.11 3.6
Confirmatory 20 16 412.9→169
Primary 15 32 398.9→80.1
PFHxS 7.39 1
Confirmatory 15 32 398.9→99.1
Primary 15 10 362.9→319
PFHpA 6.35 4.1
Confirmatory 15 15 362.9→169
Primary 15 8 312.9→269
PFHxA 5.54 24.1
Confirmatory 15 18 312.9→119.1
Primary 10 30 298.9→80.1
PFBS 5.66 1.6
Confirmatory 10 25 298.9→99.1
PFPeA Primary 4.68 10 8 263→219 NA
PFBA Primary 3.67 10 8 212.9→169 NA
Primary 15 20 376.9→293
FHEA 6.14 3.6
Confirmatory 15 6 376.9→313
Primary 15 18 476.9→393
FOEA 7.54 4.3
Confirmatory 15 12 476.9→413
Primary 15 8 576.8→493
FDEA 8.83 3.2
Confirmatory 15 15 576.8→513
FOUEA Primary 7.54 20 12 456.9→392.9 NA
Primary 15 12 440.9→337
FHpPA 7.54 1.1
Confirmatory 15 20 440.9→317
FHUEA Primary 6.08 10 12 357→293 NA
MPFBA Primary 3.67 10 7 217→172.1 NA
MPFHxA Primary 5.54 15 8 315→270 NA
MPFHxS Primary 7.39 15 34 402.9→84.1 NA
MPFOA Primary 7.11 15 10 417→372 NA
MPFNA Primary 7.81 15 9 467.9→423 NA
MPFOS Primary 8.78 15 40 502.9→80.1 NA
MPFDA Primary 8.45 15 10 514.9→470 NA
MPFUnA Primary 9.05 15 10 564.9→519.9 NA
MPFDoA Primary 9.61 15 12 614.9→569.9 NA
D7968 − 23
SRM transition. As an additional quality control measure, determine these compounds at trace levels in various soil
isotopically labeled PFAS surrogate (listed in 12.4) recoveries matrices for understanding of the sources and pathways of
are monitored. There is no correction to the data based upon exposure.
surrogate recoveries. The final report issued for each sample
5.3 This method has been used to determine selected PFAS
lists the concentration of PFAS, if detected, or in sand (Table 4) and four ASTM reference soils (Table 5).
quantifiable, in ng/kg (dry weight basis) and the surrogate
recoveries.
6. Interferences
5. Significance and Use 6.1 All glassware is washed in hot water with detergent and
rinsed in hot water followed by distilled water. The glassware
5.1 This test method has been developed by the U.S. EPA
is then dried and heated in an oven at 250 °C for 15 to 30 min.
Region 5 Chicago Regional Laboratory (CRL).
All glassware is subsequently rinsed with methanol or acetoni-
5.2 PFAS are widely used in various industrial and com-
trile.
mercial products; they are persistent, bio-accumulative, and
6.2 All reagents and solvents should be pesticide residue
ubiquitous in the environment. PFAS have been reported to
purity or higher to minimize interference problems. The use of
exhibit developmental toxicity, hepatotoxicity,
PFAS-containing caps must be avoided.
immunotoxicity, and hormone disturbance. A draft Toxicologi-
cal Profile for Perfluoroalkyls from the U.S. Department of
6.3 Matrix interferences may be caused by contaminants in
Health and Human Services is available. PFAS have been
the sample. The extent of matrix interferences can vary
detected in soils, sludges, and surface and drinking waters.
considerably depending on variations in the sample matrices.
Hence, there is a need for a quick, easy, and robust method to
6.4 Contaminants have been found in reagents, glassware,
tubing, glass disposable pipettes, filters, degassers, and other
apparatus that release polyfluorinated compounds. All of these
7 materials and supplies are routinely demonstrated to be free
A draft Toxicological Profile for Perfluroalkyls can be found at http://
www.atsdr.cdc.gov/toxprofiles/tp.asp?id=1117&tid=237 (2014).
TABLE 4 Single-Laboratory Recovery Data in Ottawa Sand
Measured ng/kg from Ottawa Sand P&A Data (400 ng/kg spike for all PFAS except 2000 ng/kg for PFBA and PFPeA and 8000 ng/kg spike for FHEA,
FDEA, and FOEA)
Sample
PFTreA PFTriA PFDoA PFUnA PFDA PFNA PFOA PFHpA PFHxA PFPeA PFBA
Unspiked Unspiked P&A 1 389.6 394.3 384.7 376.7 362.1 347.6 345.8 232.9 222.2 1614.9 1344.5
P&A 2 462.1 424.6 397.2 379.1 378.4 376.9 365.9 247.9 229.8 1710.1 1388
P&A 3 402.7 387.7 383.1 365.9 374.7 363.3 347.1 242.4 222.9 1658.9 1376
P&A 4 403.9 397.1 395.4 381.5 379 359.4 342.7 246.8 225.8 1693.6 1401.9
P&A 5 467.2 445.8 412.6 388.5 376.8 370.3 369.7 249.3 231.4 1716.5 1433.4
P&A 6 392.1 385.3 374.2 370.9 353.2 351.7 340.3 236.7 220.5 1659 1366.4
Mean
Recovery 419.6 405.8 391.2 377.1 370.7 361.5 351.9 242.7 225.4 1675.5 1385
(ng/kg)
% Mean 104.9 101.4 97.8 94.3 92.7 90.4 88 60.7 56.4 83.8 69.3
Recovery
Standard 35.4 24.1 13.5 8 10.6 11.1 12.6 6.6 4.4 38.5 30.7
Deviation
RSD (%) 8.4 5.9 3.5 2.1 2.9 3.1 3.6 11 1.9 2.3 2.2
Sample PFBS PFHxS PFOS PFechS FOUEA FHpPA FHUEA FHEA FOEA FDEA
Unspiked Unspiked P&A 1 337.4 349.1 340.3 342.8 389.5 371.3 372.5 7023.5 8202.6 8564.9
P&A 2 347.3 358.3 345.9 347.2 408.7 377.2 387.1 7346.1 8542.6 9308
P&A 3 366.3 330.1 331.7 345.4 401.5 361.4 379 6844.3 7402.4 8989.2
P&A 4 348.2 343.6 338.3 347.6 404.9 377.5 388.1 7258.2 7551.9 9173.4
P&A 5 351.8 361.7 365.6 362.6 417.5 395.1 391.8 7461.3 7821.2 9287.4
P&A 6 336.7 343.4 363.7 342.5 394.5 356.9 374.5 7559.3 8002.2 8367.1
Mean
Recovery 347.9 347.7 347.7 348 402.7 373.2 382.1 7248.8 7920.5 8948.3
(ng/kg)
% Mean 87 86.9 86.9 87 100.7 93.3 95.5 90.6 99 111.9
Recovery
Standard 10.9 11.5 13.9 7.4 10 13.6 7.9 270.4 421.3 395.3
Deviation
RSD (%) 3.1 3.3 4 2.1 2.5 3.6 2.1 3.7 5.3 4.4
D7968 − 23
TABLE 5 Single-Laboratory Surrogate Recovery Data in Ottawa Sand
Measured ng/kg from Ottawa Sand – 400 ng/kg spike
Sample
MPFBA MPFHxA MPFHxS MPFOA MPFNA MPFOS MPFDA MPFUnA MPFDoA
Unspiked 1 420.0 433.5 431.8 428.0 439.4 429.2 442.6 443.3 447.7
Unspiked 2 366.5 396.8 378.5 384.9 389.8 373.6 404.9 400.8 425.8
P&A 1 361.1 364.3 356.3 377.0 376.6 354.4 384.9 391.3 409.3
P&A 2 383.6 378.4 357.3 389.4 379.7 375.7 395.7 399.2 412.2
P&A 3 374.5 378.5 375.4 390.5 378.6 372.4 382.5 386.9 402.2
P&A 4 370.1 384.4 366.1 396.3 384.4 374.2 397.8 406.2 420.5
P&A 5 370.1 386.8 372.0 395.7 381.1 372.8 394.4 399.9 421.5
P&A 6 363.6 384.8 356.1 397.9 384.9 368.6 389.5 392.3 402.9
Mean
Recovery
376.2 388.4 374.2 394.9 389.3 377.6 399.0 402.5 417.7
(ng/kg dry
weight)
% Mean 94.0 97.1 93.5 98.7 97.3 94.4 99.8 100.6 104.4
Recovery
Standard 19.0 20.4 24.9 15.0 20.7 21.9 19.0 17.6 14.9
Deviation
RSD (%) 5.1 5.3 6.7 3.8 5.3 5.8 4.8 4.4 3.6
from interferences by analyzing laboratory reagent blanks may be used. The retention times and order of elution may
under the same conditions as the samples. If found, measures change depending on the column used and need to be moni-
should be taken to remove the contamination or data should be tored.
qualified; background subtraction of blank contamination is not
7.1.3 Isolator Column—A reverse phase C18 column was
allowed.
used in this test method to separate the target analytes in the LC
system and solvents from the target analytes in the analytical
6.5 The liquid chromatography system used should consist,
sample. This column was placed between the solvent mixing
as much as practical, of sample solution or eluent contacting
chamber and the injector sample loop.
components free of PFAS target analytes of interest.
7.2 Tandem Mass Spectrometer System—An MS/MS system
6.6 Polyethylene LC vial caps or any other target analyte-
capable of multiple reaction monitoring (MRM) analysis or
free vial caps should be used.
any system that is capable of meeting the requirements in this
6.7 Polyethylene disposable pipettes or target analyte-free
test method must be used.
pipettes should be used. All disposable pipettes should be
7.3 Centrifuge—A device to centrifuge the samples.
checked for release of target analytes of interest.
6.8 Degassers are important to continuous LC operation and
7.4 Lab Rotator —A device to mix the samples by end-
most commonly are made of fluorinated polymers. To enable over-end rotation.
use, an isolator column should be placed after the degasser and
7.5 Filtration Device:
prior to the sample injection valve to separate the PFAS in the
7.5.1 Hypodermic Syringe—A luer-lock tip glass syringe
sample from the PFAS in the LC system.
capable of holding a syringe-driven filter unit.
7.5.2 A 10 mL lock tip glass syringe size is recommended
7. Apparatus
since a 10 mL sample size is used in this test method.
7.1 LC/MS/MS System:
7.5.3 Filter Unit —Polypropylene filter units were used to
7.1.1 Liquid Chromatography System—A complete LC sys-
filter the samples.
tem is required in order to analyze samples; this should include
a sample injection system, a solvent pumping system capable
8. Reagents and Materials
of mixing solvents, a sample compartment capable of main-
taining required temperature, and a temperature-controlled
8.1 Purity of Reagents—High performance liquid chroma-
column compartment. An LC system that is capable of per-
tography (HPLC) pesticide residue analysis and spectropho-
forming at the flows, pressures, controlled temperatures,
tometry grade chemicals must be used in all tests. Unless
sample volumes, and requirements of the standard must be
indicated otherwise, it is intended that all reagents must
used.
conform to the Committee on Analytical Reagents of the
7.1.2 Analytical Column —A reverse phase Charged Sur-
American Chemical Society. Other reagent grades may be
face Hybrid Phenyl-Hexyl particle column was used to develop
this test method. Any column that achieves adequate resolution
A lab rotator, or equivalent, has been found suitable to mix samples.
8 10
A Waters Acquity UPLC CSH Phenyl-Hexyl, 2.1 × 100 mm and 1.7 μm particle A 0.2 μm polypropylene membrane syringe-driven filter unit, or equivalent,
size column, or equivalent, has been found suitable for use. It was used to develop has been found suitable for use.
this test method and generate the precision and bias data presented in Section 16. If Reagent Chemicals, American Chemical Society Specifications, American
you are aware of an alternative column that meets the performance of the standard, Chemical Society, Washington, D.C. For suggestions on the testing of reagents not
please provide this information to ASTM International Headquarters. Your com- listed by the American Chemical Society, see Analar Standards for Laboratory
ments will receive careful consideration at the meeting responsible technical Chemicals, EDH Ltd., Poole, Dorset, U.K. and the United States Pharmacopeia and
committee, which you may attend. National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
D7968 − 23
used provided they are first determined to be of sufficiently 8.19.14 Perfluorotetradecanoate (PFTreA, CAS No. 376-06-
high purity to permit their use without affecting the accuracy of 7).
the measurements. 8.19.15 Decafluoro-4-
(pentafluoroethyl)cyclohexanesulfonate (PFechS, CAS No.
8.2 Purity of Water—Unless otherwise indicated, references
67584-42-3).
to water must be understood to mean reagent water conforming
8.19.16 3-perfluoropheptyl propanoic acid (FHpPA, CAS
to Type I of Specification D1193. It must be demonstrated that
No. 812-70-4).
this water does not contain contaminants at concentrations
8.19.17 2H-perfluoro-2-decenoic acid (FOUEA, CAS No.
sufficient to interfere with the analysis.
70887-84-2).
8.3 Gases—Ultrapure nitrogen and argon.
8.19.18 2-perfluorodecyl ethanoic acid (FDEA, CAS num-
ber not available).
8.4 Vials—2 mL amber glass or polypropylene autosampler
vials or equivalent. 8.19.19 2-perfluorooctyl ethanoic acid (FOEA, CAS No.
27854-31-5).
8.5 Polyethylene or any PFAS-free applicable autosampler
8.19.20 2H-perfluoro-2-octenoic acid (FHUEA, CAS num-
vial caps.
ber not available).
8.6 Syringe—10 or 25 mL filter-adaptable glass syringe with
8.19.21 2-perfluorohexyl ethanoic acid (FHEA, CAS No.
luer lock.
53826-12-3).
8.7 pH paper (pH range 1 to 14).
8.20 PFAS Surrogates:
8.20.1 O -Perfluorohexylsulfonate (MPFHxS).
8.8 Polypropylene Tubes—15 and 50 mL.
8.20.2 C -Perfluorooctylsulfonate (MPFOS).
8.9 Class A volumetric glassware.
8.20.3 C -Perfluorobutanoate (MPFBA).
8.10 Pipette Tips—Polypropylene pipette tips free of release
8.20.4 C -Perfluorohexanoate (MPFHxA).
agents or low retention coating of various sizes.
8.20.5 C -Perfluorooctanoate (MPFOA).
8.20.6 C -Perfluorononanoate (MPFNA).
8.11 Polyethylene disposable pipettes. 5
8.20.7 C -Perfluorodecanoate (MPFDA).
8.12 Acetonitrile (CAS No. 75-05-8).
8.20.8 C -Perfluoroundecanoate (MPFUnA).
8.13 Methanol (CAS No. 67-56-1).
8.20.9 C -Perfluorododecanoate (MPFDoA).
8.14 Ammonium acetate (CAS No. 631-61-8).
9. Hazards
8.15 Acetic acid (CAS No. 64-19-7).
9.1 Normal laboratory safety applies to this method. Ana-
8.16 2-Propanol (isopropyl alcohol, CAS No. 67-63-0).
lysts should wear safety glasses, gloves, and lab coats when
working in the lab. Analysts should review the Safety Data
8.17 Ammonium hydroxide (CAS No. 1336-21-6).
Sheets (SDS) for all reagents used in this method.
8.18 Ottawa sand (CAS No. 14808-60-7).
8.19 PFAS Standards: 10. Sampling
8.19.1 Perfluorobutylsulfonate (PFBS, CAS No. 29420-49-
10.1 Sampling and Preservation—Grab samples are col-
3).
lected in glass or polypropylene containers. Sample containers
8.19.2 Perfluorohexylsulfonate (PFHxS, CAS No. 3871-99-
and contact surfaces with PFAS must be avoided. As part of the
6).
overall quality assurance program for this test method, field
8.19.3 Perfluorooctylsulfonate (PFOS, CAS No. 1763-23-
blanks exposed to the same field conditions as samples are
1).
collected and analyzed according to this test method to assess
8.19.4 Perfluorobutanoate (PFBA, CAS No. 375-22-4).
the potential for field contamination. This test method is based
8.19.5 Perfluoropentanoate (PFPeA, CAS No. 2706-90-3).
on a 2 g sample size per analysis. If different sample sizes are
8.19.6 Perfluorohexanoate (PFHxA, CAS No. 307-24-4).
used, spiking solution amounts may need to be modified.
8.19.7 Perfluoroheptanoate (PFHpA, CAS No. 375-85-9).
Conventional sampling practices should be followed with the
8.19.8 Perfluorooctanoate (PFOA, CAS No. 335-67-1).
caution that PFAS-containing products may be present in
8.19.9 Perfluorononanoate (PFNA, CAS No. 375-95-1)
sampling equipment. All sampling equipment and supplies
8.19.10 Perfluorodecanoate (PFDA, CAS No. 335-76-2).
must be PFAS free in order to prevent contamination of the
8.19.11 Perfluoroundecanoate (PFUnA, CAS No. 2058-94-
samples. EPA publication SW-846 may be used as a sampling
8).
guide. Samples must be shipped on ice with a trip blank. Once
8.19.12 Perfluorododecanoate (PFDoA, CAS No. 307-55-
received, the sample temperature is taken and must be between
1).
freezing and 6 °C. If the receiving temperature is greater than
8.19.13 Perfluorotridecanoate (PFTriA, CAS No. 72629-94-
6 °C, the sample temperature is noted in the case narrative
8).
accompanying the data. Samples should be stored refrigerated
between 0 and 6 °C from the time of collection until analysis.
PFAS standards may be difficult to find; some sources of PFAS standards that
have been found suitable for use were from Aldrich Chemical Company,
Accustandard, Wellington Laboratories, Inc., and Wako Laboratory. Standards from PFAS surrogates from Wellington Laboratories Inc., or equivalent, have been
other vendors may be used. found suitable for use.
D7968 − 23
The sample should be analyzed within 28 days of collection. 11.3.1.6 Desolvation Gas Temperature: 450 °C.
No holding time study has been done on the various soil 11.3.1.7 Desolvation Gas Flow: 800 L/h.
matrices tested in this test method. Holding time may vary 11.3.1.8 Cone Gas Flow: 200 L/h.
depending on the matrix, and individual laboratories should 11.3.1.9 Collision Gas Flow: 0.15 mL/min.
determine the holding time in their matrix. 11.3.1.10 Low Mass Resolution 1: 2.6.
11.3.1.11 High Mass Resolution 1: 14.
11. Preparation of LC/MS/MS
11.3.1.12 Ion Energy 1: 1.
11.3.1.13 Entrance Energy: 1.
11.1 LC Chromatograph Operating Conditions:
11.3.1.14 Collision Energy: Variable depending on analyte.
11.1.1 Injections of all standards and samples are made at a
11.3.1.15 Exit Energy: 1.
30 μL volume. Other injection volumes may be used to
11.3.1.16 Low Mass Resolution 2: 2.5.
optimize conditions. Standards and sample extracts must be in
11.3.1.17 High Mass Resolution 2: 14.
a 50:50 methanol:water solution containing 0.1 % acetic acid.
In the case of extreme concentration differences amongst 11.3.1.18 Ion Energy 2: 3.
11.3.1.19 Gain: 1.0.
samples, it is wise to analyze a blank after a concentrated
sample and before a dilute sample to minimize carryover of 11.3.1.20 Multiplier: 511.1.
11.3.1.21 Inter-Scan Delay: 0.004 s.
analytes from injection to injection. However, there should not
be carryover between samples. The LC utilized to develop this
test method has a flow-through LC needle design. The gradient 12. Calibration and Standardization
conditions for liquid chromatography are shown in Table 6.
12.1 The mass spectrometer must be calibrated as per
11.2 LC Sample Manager Conditions: manufacturer’s specifications before analysis. Analytical val-
11.2.1 Needle Wash Solvent—60 % acetonitrile/40 % ues satisfying test method criteria have been achieved using the
2-propanol; Time: 5 min.
following procedures. Prepare all solutions in the lab using
Class A volumetric glassware.
11.3 Mass Spectrometer Parameters:
11.3.1 To acquire the maximum number of data points per
12.2 Calibration and Standardization—To calibrate the
SRM channel while maintaining adequate sensitivity, the tune instrument, analyze nine calibration standards of the polyfluo-
parameters may be optimized according to the instrument used.
rinated compounds prior to sample analysis as shown in Table
Each peak requires at least ten scans per peak for adequate 2. Calibration stock standard solution is prepared from the
quantitation. This test method contains nine surrogates, which
target and surrogate spike solutions directly to ensure consis-
are isotopically labeled PFAS, and 21 PFAS which are split up tency. Stock standard Solution A containing the polyfluorinated
into 18 MRM acquisition functions to optimize sensitivity.
compounds and surrogates is prepared at Level 9 concentration
Variable parameters regarding retention times, SRM and aliquots of that solution are diluted to prepare Levels 1
transitions, and cone and collision energies are shown in Table
through 8. The following steps will produce standards with the
3. Mass spectrometer parameters used in the development of concentration values shown in Table 2. The analyst is respon-
this method are listed below: sible for recording initial component weights carefully when
11.3.1.1 The instrument is set in the Electrospray negative working with pure materials and correctly carrying the weights
source setting. through the dilution calculations. At a minimum five calibra-
11.3.1.2 Capillary Voltage: 0.75 kV. tion levels are required when using a linear calibration curve
11.3.1.3 Cone: Variable depending on analyte. and six calibration levels are required when using a quadratic
11.3.1.4 Extractor: 2 Volts. calibration curve. An initial nine-point curve may be used to
11.3.1.5 Source Temperature: 150 °C. allow for the dropping of the lower level calibration points if
the individual laboratory’s instrument cannot achieve low
detection limits on certain PFAS. This should allow for at least
A guide to help and determine sample holding times can be found at
a five or six-point calibration curve to be obtained. No
http://www.epa.gov/esd/cmb/research/bs_033cmb06.pdf (2014).
problems were encountered while using the nine-point calibra-
tion curve in developing this test method.
TABLE 6 Gradient Conditions for Liquid Chromatography
12.2.1 Calibration stock standard Solution A (Level 9, Table
Percent
2) is prepared from the target and surrogate spike solutions
95 % Water:
Percent directly to ensure consistency. 500 μL of surrogate spike
5 %
Time Flow 95 % Water: Percent
Acetonitrile, (20 μg ⁄L), 500 μL Target Spike I, and 500 μL of PFAS Target
(min) (mL/min) 5 % Acetonitrile
400 mM
Spike II (refer to Table 7) is added to a 50 mL volumetric flask
Acetonitrile
Ammonium
and diluted to 50 mL with 50:50 methanol:water containing
Acetate
0 0.3 95 0 5 0.1 % acetic acid. The preparation of the Level 9 standard can
1 0.3 75 20 5
be accomplished using appropriate volumes and concentrations
6 0.3 50 45 5
of stock solutions as per a particular laboratory’s standard
13 0.3 15 80 5
14 0.4 0 95 5 procedure. It is critical to ensure that analytes are solubilized in
17 0.4 0 95 5
the Level 9 standard.
18 0.4 95 0 5
12.2.2 Aliquots of Solution A are then diluted with 50:50
21 0.4 95 0 5
methanol:water containing 0.1 % acetic acid to prepare the
D7968 − 23
TABLE 7 PFAS Target Spike Solutions (PPB)
Concentration of Analyte in PFAS Target Spike Solutions
Analyte PFAS High Target Spike Solutions
PFAS Reporting Limit Spike Solution
Target Spike I Target Spike II
PFTreA, PFTriA, PFDoA, PFUnA,
PFDA, PFOS, PFNA, PFHxA, PFHpA, 20 μg/L — 2 μg/L
PFBS, PFechS, PFOA, PFHxS
PFBA, PFPeA 100 μg/L — 10 μg/L
FOUEA, FHUEA, FHpPA — 20 μg/L 2 μg/L
FHEA, FOEA, FDEA — 400 μg/L 40 μg/L
desired calibration levels in 2 mL LC vials. The calibration 12.2.6 Linear calibration may be used if the point of origin
vials must be used within 24 h to ensure optimum results. The is excluded and a fit weighting 1/X is used in order to give
end calibration check must be prepared in a separate LC vial
more emphasis to the lower concentrations. Each calibration
near the mid-level. All calibration standards should only be point used to generate the curve must have a calculated percent
used once. The analyte concentration in the vial may change
deviation less than 25 % from the generated curve.
after the vial cap is pierced because the vial caps may not reseal
12.2.7 Quadratic calibration may be used if the point of
after puncture; if the cap reseals it may be used over again.
origin is excluded, and a fit weighting of 1/X is used in order
Changing the caps immediately after the injection should
to give more emphasis to the lower concentrations. Each
alleviate this problem. Calibration standards are not filtered.
calibration point used to generate the curve must have a
12.2.3 Inject each standard and obtain its chromatogram. An
calculated percent deviation less than 25 % from the generated
external calibration technique is used to monitor the primary
curve.
and confirmatory SRM transitions of each analyte. Calibration
12.2.8 The retention time window of the SRM transitions
software is utilized to conduct the quantitation of the target
must be within 5 % of the retention time of the analyte in a
analytes and surrogates using the primary SRM transition. The
midpoint calibration standard. If this is not the case, re-analyze
ratios of the primary/confirmatory SRM transition area counts
the calibration curve to determine if there was a shift in
are given in Table 3 and will vary depending on the individual
retention time during the analysis and the sample needs to be
tuning conditions. The primary/confirmatory SRM transition
re-injected. If the retention time is still incorrect in the sample,
area ratio must be within 35 % of the individual lab’s accepted
refer to the analyte as an unknown.
primary/confirmatory SRM transition area ratio. The primary
12.2.9 A midpoint calibration check standard must be ana-
SRM transition of each analyte is used for quantitation of and
lyzed at the end of each batch of 30 samples or within 24 h
the confirmatory SRM transition for confirmation. This gives
after the initial calibration curve was generated; the criteria in
added confirmation by isolating the parent ion, forming two
the individual lab’s quality system may be more restrictive
product ions via fragmentation, and relating it to the retention
pertaining to the number of samples. This end calibration
time in the calibration standard.
check, a new not pierced sealed vial, should come from the
12.2.4 Depending on sensitivity and matrix interference
same calibration standard solution that was used to generate the
issues dependent on sample type, the confirmatory SRM
initial curve. The results from the end calibration check
transition can be used as the primary SRM transition for
standard must have a percent deviation less than 30 % from the
quantitation during analysis. This must be explained in a
calculated concentration for the target analytes and surrogates.
narrative accompanying the data. A new primary/confirmatory
If the results are not within these criteria, corrective action
ion ratio will then be determined if switching the SRM
including reoccurrence minimization is performed and either
transitions used to quantitate and confirm. The new primary/
all samples in the batch are re-analyzed against a new
confirmatory SRM transition area ratio is required to be within
calibration curve or the affected results are qualified with an
35 % of the individual lab’s new primary/confirmatory SRM
indication that they do not fall within the performance criteria
transition area ratio.
of the test method. If the analyst inspects the vial containing
12.2.5 The calibration software manual should be consulted
the end calibration check standard and notices that the sample
to use the software correctly. The quantitation method is set as
evaporated affecting the concentration or other anomaly, a new
an external calibration using the peak areas in ppt units.
end calibration check standard may be made and analyzed. If
Concentrations may be calculated using the data system
this new end calibration check standard has a percent deviation
software to generate linear regression or quadratic calibration
less than 30 % from the calculated concentration for the target
curves. Forcing the calibration curve through the origin (X = 0,
analytes and surrogates, the results may be reported unquali-
Y = 0) is not recommended. Curves should be evaluated using
15 fied.
relative error or relative standard error.
12.3 If a laboratory has not performed the test before or if
there has been a major change in the measurement system, for
Management and Technical Requirements for Laboratories Performing Envi-
example, new analyst, new instrument, etc., an instrument
ronmental Analysis, Module 4: Quality Systems for Chemical Testing; The NELAC
Institute, 2017. qualification study including method detection limit (MDL),
D7968 − 23
calibration range determination, and precision and bias deter- method. References generating QC acceptance criteria are
mination must be performed to demonstrate laboratory capa- ASTM Practices D2777, D5847, E2554, or Method 8000 in
bility. EPA publication SW-846.
12.3.1 Analyze at least four replicates of a spiked sand
12.4 Surrogate Spiking Solution:
sample containing the PFAS and surrogates at an extract
12.4.1 A surrogate spiking solution containing nine isotopi-
concentration in the calibration range of Levels 4 through 7.
cally labeled PFAS—MPFBA, MPFHxA, MPFHxS, MPFDA,
The Level 6 concentration of the nine-point calibration curve
MPFOA, MPFOS, MPFNA, MPFUnA, and MPFDoA—is
was used to set the QC acceptance criteria in this method. The
added to all samples, method blanks, duplicates, laboratory
matrix and chemistry should be similar to the matrix used in
control samples, matrix spikes, and reporting limit checks. A
this test method. Each replicate must be taken through the
stock surrogate spiking solution is prepared at 20 μg/L in 95 %
complete analytical test method including any sample manipu-
acetonitrile: 5 % water. Spiking 40 μL of this spiking solution
lation and extraction steps.
into a 2 g soil sample results in a concentration of 400 ng/kg of
12.3.2 Calculate the mean (average) percent recovery and
the surrogate in the sample. The results obtained for the
relative standard deviation (RSD) of the four values and
surrogate recoveries must fall within the limits of Table 8. If
compare to the acceptable ranges of the QC acceptance criteria
the limits are not met, the affected results must be qualified
for the Initial Demonstration of Performance in Table 8.
with an indication that they do not fall within the performance
12.3.3 This study should be repeated until the single-
criteria of the test method.
operator precision and mean recovery are within the limits in
12.4.1.1 The surrogate spiking solution was prepared by
Table 8. If a concentration other than the recommended
adding 500 μL of a 2 mg/L PFAS surrogate mix in a 50 mL
concentration is used, refer to Practice D5847 for information
volumetric and diluted to 50 mL with 95 % acetonitrile: 5 %
on applying the F test and t test in evaluating the acceptability
water. Surrogate spiking solutions are routinely replaced every
of the mean and standard deviation.
year if not previously discarded for quality control failure.
12.3.3.1 The QC acceptance criteria for the Initial Demon-
12.5 Method Blank:
stration of Performance in Table 8 were generated from the
single-laboratory data shown in Section 16. Data from Ottawa
sand and four ASTM soil matrices are shown in Section 16. It
is recommended that each laboratory determine in-house QC 16
Surrogate mix from Wellington Laboratories, Inc. has been found suitable for
acceptance criteria which meet or exceed the criteria in this test use.
TABLE 8 QC Acceptance Criteria
NOTE 1—Table 8 data is preliminary until a multi-lab validation study is completed.
Initial Demonstration of Performance Laboratory Control Sample
Recovery (%) Precision Recovery (%)
Analyte/Surrogate Spike Conc. ng/kg
Maximum Lower Control Limit Upper Control Limit
Lower Limit Upper Limit
% RSD (LCL) % (UCL) %
PFTreA 400 70 130 30 70 130
PFTriA 400 70 130 30 70 130
PFDoA 400 70 130 30 70 130
PFUnA 400 70 130 30 70 130
PFDA 400 70 130 30 70 130
PFOS 400 70 130 30 70 130
PFNA 400 70 130 30 70 130
PFecHS 400 70 130 30 70 130
PFOA 400 70 130 30 70 130
PFHxS 400 70 130 30 70 130
PFHpA 400 50 130 30 50 130
PFHxA 400 50 130 30 50 130
PFBS 400 70 130 30 70 130
PFPeA 2000 70 130 30 70 130
PFBA 2000 50 130 30 50 130
FHEA 8000 70 130 30 70 130
FOEA 8000 70 130 30 70 130
FDEA 8000 70 130 30 70 130
FOUEA 400 70 130 30 70 130
FHpPA 400 70 130 30 70 130
FHUEA 400 70 130 30 70 130
MPFBA 400 70 130 30 70 130
MPFHxA 400 70 130 30 70 130
MPFHxS 400 70 130 30 70 130
MPFOA 400 70 130 30 70 130
MPFNA 400 70 130 30 70 130
MPFOS 400 70 130 30 70 130
MPFDA 400 70 130 30 70 130
MPFUnA 400 70 130 30 70 130
MPFDoA 400 70 130 30 70 130
D7968 − 23
12.5.1 At least two method blanks for every 30 samples are I and II in 95 % acetonitrile: 5 % water containing the 21 PFAS
prepared in 2 g of Ottawa sand to investigate for contamination at concentrations listed in Table 7. Spike 40 μL of these stock
during sample preparation and extraction. The concentration of solutions into 2 g of the site sample to yield a concentration of
target analytes in either/both blank(s) must be at less than half 2000 ng/kg (PFBA and PFPeA), 8000 ng/kg (FHEA, FDEA,
the reporting limit or the data must be qualified as having a and FOEA), and 400 ng/kg of remaining 16 PFAS (PFTreA,
blank issue and the reporting limit must be raised to at least PFTriA, PFDoA, PFUnA, PFDA, PFOS, PFNA, PFHxA,
three times above the blank contamination concentration. PFHpA, PFBS, PFechS, PFOA, PFHxS, FOUEA, FHUEA,
PFAS are common in the environment and laboratories requir- AND FHpPA) in the sample.
ing an additional method blank sample. 12.8.2 If the spiked concentration plus the background
concentration exceeds that of the Level 9 calibration standard,
12.6 Reporting Limit Check Sample (RLCS):
the sample must be diluted (using 50 % Methanol/50 % Water
12.6.1 Each batch or within the 24 h analysis window a
with 0.1 % acetic acid) to a level near the midpoint of the
reporting limit check sample must be analyzed. The reporting
calibration curve.
limit check sample is processed like a laboratory control
12.8.3 Calculate the percent recovery of the spike (P) using
sample just spiked at or near (one to two times) the reporting
Eq 1:
limit. The concentration of the RLCS may be reported below
A V 1 V 2 BV
~ !
? s s?
the reporting limit since the spike is at or near the reporting
P 5 100 (1)
CV
limit. This sample is to check if the analytes were present at the
reporting limit, they would be identified. The recovery limits
where:
for the RLCS are 35 to 150 %, if any analytes are outside of
A = concentration found in spiked sample,
these limits the QC failure is explained in a narrative accom-
B = concentration found in unspiked sample,
panying the data.
C = concentration of analyte in spiking solution,
12.6.2 Two grams of Ottawa sand is added to a 15 mL
V = volume of sample used,
s
polypropylene centrifuge tube. The sample is spiked with
V = volume of spiking solution added, and
40 μL of PFAS surrogate spiking solution and 25 μL of PFAS P = percent recovery.
reporting limit check solution (Table 7) and then taken through
12.8.4 The percent recovery of the spike must fall within the
the sample preparation and analyzed.
limits in Table 9. If the percent recovery is not wit
...