Presentation on PFAS method variability across the analytical community outlining impacts to data comparability

1. Presentation Title
Subtitle / Author
Which Method
Should/Did You Use
for PFAS?
AEHS
29th Annual International
Conference
March 21, 2019
David A. Gratson, CEAC
Rock J. Vitale, CEAC
David R. Blye, CEAC
Meg A. Michell

2. Agenda
 Issues
 Chemistry
 Methods of Analysis
 Variations on a theme
that impact data comparability
ISO
DoD
Strict US
EPA
ASTM
Modified
Method
Availability of
Standards
Calibration
Sample
Performance
Monitoring
Extraction Analysis Reporting

3. PFAS Issues – Big Picture
 Laboratories are being requested to analyze for
per/polyfluoroalkyl substances (PFAS) in matrices that
have no approved US EPA methodology.
 Laboratory accreditation/oversight is lacking.
 These differences lead to poor data comparability.
 Industries and agencies are under pressure for
information.
 US EPA has been slow to develop/validate methods.
 US EPA Action Plan
 Decisions are being made using data of unknown
quality.

4. PFAS Chemistry - Structures
 PFOA

5. PFAS Structures
 Per/Polyfluoroalkyl
Substances
Carboxylates
(A, e.g., PFOA)
Sulfonates (B,
e.g., PFOS)
Fluorotelomer
(C, e.g.,
8:2 FtS)

6. PFAS Structures
 Sulfonamido Substances
(+ & -, aka FOSA), (D)
 Other (E)
PFOSA
More at: https://www.atsdr.cdc.gov/pfas/and https://www.itrcweb.org/Team/Public?teamID=78

7. World of Methods
 ISO 25101, aqueous (2009)
 Rarely used in the U.S.
 ASTM D7968-17a
 Soil, single laboratory only
 ASTM D7979 – 17
 Water, Sludge, Influent, Effluent and Wastewater
single laboratory only
 Department of Defense (DoD)
 Quality Systems Manual (QSM)
 aqueous
 soil/solids
ASTM
DoD
ISO

8. World of Methods (Cont.)
 US EPA Method 537 – Drinking Water,
just revised November 2018
 Coming (Q1 2019?)
 US EPA 8327
 water only, direct injection, screening
 US EPA 8328
 water/soil/sediment, solid-phase extraction (SPE),
isotopic dilution
 US EPA 8329
 Air, biota, food: no published/validated methods
Modified
Method
Strict US
EPA

9. PFAS Analytes vs. Method
PFAS Class 537.1
Drinking Water Only
537
Modified*
DoD QSM 5.2
Number of Analytes 18 18-50+ Per laboratory
A (Carboxylates) 9 (C4-C14) Yes Yes
B (Sulfonates) 5 (2 with ether
group)
Yes Yes
C (Fluorotelomer) 0 Likely Likely
D (Sulfonamido
Substances)
2 Likely Likely
E (Other) 2 ? ?
Notes Attempted to
include more
analytes, poor SPE
recovery
As a standard
becomes
available
Prescribed QC Table B.15
Other: ADONA, HFPO-DA (GenX component)

10. PFAS Analytes vs. Method (Cont.)
PFAS Class ASTM D7968-17a ASTM D7979-17
Number of Analytes 21 + 21 +
A (Carboxylates) 11 (C4-C14) 11 (C4-C14)
B (Sulfonates) 3 (C4, C6, C8), + 1 cyclic 3 (C4, C6, C8), + 1 cyclic
C (Fluorotelomer) 6 6
D (Sulfonamido
Substances)
0* 0*
E (Other) 0 0
Notes Performance based, could add
compounds
Performance based, could add
compounds
* Listed as likely applicable analytes

11. LC/MS/MS – 3 dimensions of separation

12. 12
LC/MS and LC/MS/MS
Mass Transition

13. Analytical
Issues Availability of
Standards
Calibration
Sample
Performance
Monitoring
Extraction
Analysis Reporting

14. Standards
 US EPA Method 537 and DoD QSM indicate that
standards should include linear and branched
isomers unless unavailable.
 ASTM methods do not specify linear and branched
isomers in the calibration standard section
(assumed later in methods).
 Majority of standards will include linear, methyl
isomers, and dimethyl isomers only.
 Standards are not available with branched isomers
for a number of PFAS target compounds.

15. Standards (Cont.)
 Limited number of isotope-labeled compounds are
available.
 Laboratories do not always utilize all available
standards.
 Mass transitions that are monitored are variable.
 Some monitor one transition mass.
 Fewer monitor two transition masses.

16. Calibration Technique Variability
 External standard
 Target response ratio with target concentration
 Internal standard
 Target internal response ratio with target/internal concentration
 Internal added post sample extraction and concentration
 Isotope dilution
 Isotope standard added prior to sample extraction
 Isotope/internal standard response ratio with isotope/internal
standard concentration, or maybe external standard calibration
for isotope
 Target/isotope response ratio with target/isotope concentration

17. Calibration Models
 Calibration models vary:
 Average response factor (RF) or relative response factor (RRF)
 Relative standard deviation (RSD) ≤ 20%, or 30%, or other
 Linear equation with or without weighting
 R2 ≥ 0.99, or 0.98, or other
 Quadratic equation with or without weighting
 R2 ≥ 0.99 or other
 Force curve through origin or not
 Comparability

18. Calibration Check Variability
 Some laboratories will utilize just the re-fit recovery
for acceptance.
 Continuing calibration verifications
 Daily
 Beginning and closing of sequence, every 30 analyses
 ± 20% recovery, ± 30% recovery, or other
 Calibration model and acceptance criteria impact
the calculated result

19. Extraction Techniques
• US EPA Method 537 – SPE
(drinking water only)
• ASTM Method D7979-16 and
D7979-17 (aqueous and sludge)–
methanol shake/vortex
• ASTM Method D7968-17 (soil) methanol vortex
• DoD QSM 5.1.1 and 5.2, SPE for aqueous, not specified
for other matrices
• Laboratory-specific modified methods – anything goes
SPE Schematic: https://separationmethods.com/product-category/sample-preparation/spe-cartridges/

21. Extraction Techniques
 Solid or other matrices being tested include:
 Shake/vortex or sonication
 Automated solvent extraction (not common)
 Automated Soxhlet extraction (not common)
 Microwave (not common)
Image: https://www.chemistryworld.com/opinion/classic-kit-soxhlet-extractor/3004940.article

22. Extraction Techniques (Cont.)
 Extraction solvents vary (reagent water, methanol,
acetonitrile)
 Cleanups for extracts may or may not be performed
 Extracts may be:
 Concentrated to dryness, then transferred into
solvent
 Concentrated, but not to dryness
 Not concentrated at all

23. Variability So Far
Availability of
Standards
• Linear, branched,
isotopes
Calibration
• Approach, frequency,
acceptance criteria
Extraction (chain
length, polarity, pKa)
• SPE, Liquid-liquid, shake,
sonicate

24. Sample-specific Performance Monitoring
 External standard technique
 Surrogate compounds added prior
to extraction monitors extraction
performance
 No separate instrument monitor
 Internal standard technique
 Internal standard added immediately
prior to instrument analysis
monitors instrument
 Surrogates + internal standards
Batch
Check Standards
On-Instrument
Internal Standards
Extraction
Surrogates

25. Sample-specific Performance Monitoring
 Isotope dilution technique
 Labeled compounds added prior to extraction for
isotope dilution compensate for extraction efficiency.
 Labeled compounds are used to calculate target
results.
 Internal standard added prior to analysis to
quantitate labeled compounds (well, not all
laboratories).
 Internal standard monitors instrument performance.

26. Reporting and Analyte List Variability
 Various state and federal agencies have inconsistent
analyte lists.
 Laboratories will report fewer or more PFAS analytes
than included in Method 537 (e.g., include 6:2
fluorotelomer sulfonic acid, PFBA, PFPA, etc.).
 The variability in PFAS lists between facilities makes data
comparisons more difficult.
 Chemical Abstracts Service (CAS) number use has been
variable (e.g., sulfonic acid, sulfate, or salt) and is many
times wrong.

27. How to Build Quality Data
 Due to modified methods, you must first understand
the laboratory’s approach.
 Obtain the SOPs, then review and thoroughly
understand them.
 Set up method-specific technical requirements.
 Start a performance testing (PT) sample program.
 Ensure laboratory can provide a Full data package
deliverable.
 Many laboratories performing M537 don’t have experience in
generating Full data packages.
 Verify and validate data.

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Thank You “Setting the Standards for Innovative
Environmental Solutions”
dgratson@envstd.com 505-660-8521