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PFAS Analysis: What to Expect and How to Evaluate the Data
November 8, 2019
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Methods and Analyte Lists
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PFAS MethodsMethod Year Applicable Matrices # PFAS Analytes
EPA 537 v 1.1 2009 Drinking Water 14 analytes
EPA 537.1 2018 Drinking Water 18 analytes
ASTM D7979-17 2017 Water, Wastewater 21 analytes
ASTM D7968-17 2017 Soil 21 analytes
ISO 25101 2009 Aqueous PFOA/PFOS
DoD QSM 5.1 2017 Solid & Aqueous 24+ analytes
DoD QSM 5.2 2018 Solid & Aqueous 24+ analytes
EPA 537 “Modified” Current All 24+ analytes
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Current PFAS Reportable by Analytical LaboratoriesAnaly te CAS No. UCMR3
(6)537(14)
NYSDEC(21)
ISO 25101(2)
MDEQ IPP(24)
Perfluorobutanoic acid (PFBA) 375-22-4 X XPerfluoropentanoic acid (PFPeA) 2706-90-3 X XPerfluorohexanoic acid (PFHxA) 307-24-4 X X XPerfluoroheptanoic acid (PFHpA) 375-85-9 X X X XPerfluorooctanoic acid (PFOA) 335-67-1 X X X X XPerfluorononanoic acid (PFNA) 375-95-1 X X X XPerfluorodecanoic acid (PFDA) 335-76-2 X X XPerfluoroundecanoic acid (PFUnA) 2058-94-8 X X XPerfluorododecanoic acid (PFDoA) 307-55-1 X X XPerfluorotridecanoic Acid (PFTrA) 72629-94-8 X X XPerfluorotetradecanoic acid (PFTeA) 376-06-7 X X XPerfluorohexadecanoic acid (PFHxDA) 67905-19-5Perfluorooctadecanoic acid (PFODA) 16517-11-6Perfluorobutanesulfonic acid (PFBS) 375-73-5 X X X XPerfluoropentanesulfonic acid (PFPeS) 2706-91-4 XPerfluorohexanesulfonic acid (PFHxS) 355-46-4 X X X XPerfluoroheptanesulfonic Acid (PFHpS) 375-92-8 X XPerfluorooctanesulfonic acid (PFOS) 1763-23-1 X X X X XPerfluorononanesulfonic acid (PFNS) 474511-07-4 XPerfluorodecanesulfonic acid (PFDS) 335-77-3 X XPerfluorooctane Sulfonamide (FOSA) 754-91-6 X XN-methyl perfluorooctane sulfonamidoacetic acid (NMeFOSAA) 2355-31-9 X X XN-ethyl perfluorooctane sulfonamidoacetic acid (NEtFOSAA) 2991-50-6 X X X6:2 Fluorotelomer sulfonic acid (6:2 FTSA) 27619-97-2 X X8:2 Fluorotelomer sulfonic acid (8:2 FTSA) 39108-34-4 X X4:2 Fluorotelomer sulfonic acid (4:2 FTSA) 757124-72-4 X10:2 Fluorotelomer sulfonic acid (10:2 FTSA) 120226-60-0N-Methyl perfluorooctane sulfonamidoethanol (N-MeFOSE) 24448-09-7N-Ethyl perfluorooctane sulfonamidoethanol (N-EtFOSE) 1691-99-2N-Methyl perfluorooctane sulfonamide (MeFOSA) 31506-32-8N-Ethyl perfluorooctane sulfonamide (EtFOSA) 4151-50-2HFPO-DA (Gen-X) 62037-80-3 XADONA XF-53B-9Cl XF-53B-11Cl X
Analyte lists vary by method, laboratory, and regulatory agency
Determine what list you really need!
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“Modified” EPA 537
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Typical sample result summary form
Number of PFAS reported
Results, RLs, units
Dilution results
Collection date, prepared date, analysis date
Percent solids (dry weight)
Isotope Dilution recoveries
Evaluate Holding Times14 days to extraction; 28 days from extraction to analysis
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Is the lab extracting the entire sample and rinsing the sample bottle? What cartridge is the lab using?
– Styrenedivinylbenzene (SDVB) sorbent phase– Reverse phase copolymer characterized by a weak anion exchange (WAX)
sorbent phase Is the lab doing washes to remove interferences on the SPE cartridge?
Solid Phase Extraction
250 mL sample 1 mL final extract
PFBA, PFPeA poor recoveries
DoD 5.1 vs 5.2
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Separates compound mixtures on column. Column has high affinity for PFAS. The affinity of each compound to the column is different based on its solubility.
Characteristic retention times
Step 1 in compound identification: time the compound comes off the column
Sample Analysis: HPLC Separation (Part 1)
Retention time increases with carbon number
Analyte Retention Time (min)
PFBA 1.52713C4PFBA 1.525
PFOS 3.02813C4PFOS 3.026
Retention time
DoD 5.1 vs 5.2
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Unique fragmentation patterns (Step 2 of compound identification ) Parent/daughter combinations = definitive ID, more sensitive analysis
Sample Analysis: MS/MS (Part 2)
Analyte Retention Time (min) Parent/Daughter Ions
PFBS 1.754 299/80299/99
13C3PFBS 1.752 302/83
PFOS 3.028 499/80499/99
13C4PFOS 3.026 503/809
Definitive Identification of Compounds– Retention time from HPLC separation– Transition to characteristic daughter ions– Ion ratios
What happens when the ion ratios are outside limits?– What are the limits?
What if there is no daughter/confirmation ion?– PFBA– PFPeA– NMeFOSAA– NEtFOSAA
Transition Ions (Parent/Daughter Ions)
Analyte Retention Time (min)
Parent/Daughter Ions
Ion Ratio
Ion Ratio Limit
PFBS 1.754 299/80299/99 2.91 1.35-
4.0513C3PFBS 1.752 302/83 NA NA
PFOS 3.028 499/80499/99 4.19 2.04-
6.1213C4PFOS 3.026 503/80 NA NA
DoD 5.1 vs 5.2
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Before September 2016, some inconsistency in how this performed PFHxS, PFOS, PFOA, NMeFOSAA, NEtFOSAA If branched isomers not included, result is biased low.
Linear & Branched Isomers
Correct integration of PFOA Incorrect integration of PFOA
Retention Time
Parent/daughter ions
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Sample spiked with KNOWN amount of isotopes (labeled surrogates or extracted internal standards)
Isotopes match target analytes
– 13C4PFBA is isotope associated with PFBA
– 13C4PFOS is isotope associated with PFOS
– etc. for each PFAS analyte
Target PFAS result corrected by proportional amount based on isotope
BENEFITS:
– Corrects for analytical error associated with matrix
– Corrects for matrix interferences
Isotope Dilution: What is It?
Concentration Target PFAS = Target PFAS Area * True Concentration IsotopeArea Isotope * Calibration Factor
EPA 537 and ASTM Method do NOT utilize isotope
dilution
DoD QSM requires isotope dilution
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When is the lab spiking the isotopic standards? How is the lab evaluating the recoveries of the isotopic standards?
If >10% recovery, results most likely not significantly affected. If <10% recovery, higher probability that results may be affected.
– Some data validation guidelines recommend rejecting nondetect results if <10%.
– Detected results: potential low bias– Only associated target PFAS affected
How Can Isotope Dilution Vary Between Labs?
Surrogate Lab 1 (%) Lab 2 (%) Lab 3 (%) Lab 4 (%) DoD (%)13C3-PFBS 25-150 50-150 26-148 31-159 50-150
13C3-PFHxS 25-150 50-150 34-126 47-153 50-15013C4-PFHpA 25-150 50-150 35-126 30-139 50-15013C8-PFOA 25-150 50-150 43-112 36-149 50-15013C8-PFOS 25-150 50-150 43-115 42-146 50-15013C9-PFNA 25-150 50-150 32-134 34-146 50-150
Example:If 13C3-PFBS exhibits low %R, only affects PFBS.
DoD 5.1 vs 5.2
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When samples are diluted Example: Sample contains 2000 ng/L PFOS. Isotope spiked in at 50 ng/L.
Requires a 50-fold dilution– Isotope standard now diluted out. – How will result be quantified if no recoverable isotope standard?
Lab performs dilution and then adds more of the isotope spike to the extract just prior to analysis.– Recovery of isotope 90-100%– Final result not accounting for matrix effects
If sample also analyzed undiluted or less-diluted– Recovery of isotope 50-60%– Use this recovery to correct result from diluted analysis
Correcting concentration of analyte for 90-100% versus 50-60% will result in a low-biased value
Is Isotope Dilution Ever a Problem?
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Typical sample result summary form
Number of PFAS reported
Results, RLs, units
Dilution results
Collection date, prepared date, analysis date
Percent solids (dry weight)
Isotope Dilution recoveries
PFAS Analytical Reports
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Purposes:Method Blank: To check for potential lab contamination in the sample preparation and analysis step
Field/Equipment Blanks: To check for potential contamination from ambient field conditions or equipment
Does each prep batch have its own method blank?
Blanks: Method Blanks, Field Blanks, & Equipment Blanks
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Is anything detected in the blank?
Are there any potential false positives?
General Rule of Thumb: If concentration in sample <2x the blank concentration, the result is potentially a false positive
Blank Evaluation
2x Blank = 4 ng/L
Sample conc = 7 ng/L
Real Hit
2x Blank = 4 ng/L
Sample conc = 3 ng/L
False Positive
PFOS in Blank = 2 ng/L
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Laboratory Control Samples (LCS)
• Purposes: To check the accuracy of the method in the absence of any matrix effects
• What are LCSs?
• Does each analytical or prep batch have its own LCS?
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Were all target analytes reported?
Were all recoveries within the acceptance limits?
If LCS recoveries are outside limits:– POTENTIAL LOW BIAS or– POTENTIAL HIGH BIAS
Affects the whole batch of samples prepared with the LCS.Potentially unusable results:
– if recoveries are <10%
LCS Evaluation
ACCURACY
DoD 5.1 vs 5.2
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Matrix Spikes/Matrix Spike Duplicates (MS/MSDs)
What are these? Were these analyses performed on a project sample?
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MS/MSD
• Were all target analytes reported?• Were all recoveries within the acceptance limits?
• Were all RPDs within the acceptance limits?
• If MS recoveries are outside limits:– POTENTIAL LOW BIAS or– POTENTIAL HIGH BIAS
Affects the sample that was spiked.
Potentially unusable results: – if recoveries are <10%
ACCURACY
PRECISIONDoD 5.1 vs 5.2
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Let’s Summarize Potential Biases
• Detected results Blanks
• Missed holding timesHolding Times
• Low recoveries• High recoveriesLCS
• Low recoveries• High recoveries
Labeled Surrogates, Matrix Spikes
Subsampling Water Sample
No Methanol Rinse on Bottle
HIGH BIAS
LOW BIAS
LOW BIAS HIGH BIAS
LOW BIAS HIGH BIAS
All Associated Samples in Batch}Sample-Specific}
All Associated Samples in Batch}
Sample-Specific}
LOW BIAS >C8 PFSAs & >C10 PFCAs: Sample-Specific}
LOW BIAS Long chain PFAAs : Sample-Specific}
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Detection Limits
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Different Detection Limits
Detection Limit Accurate? Precise?
Use to Demonstrate
Below Cleanup Standards?
Use Valuesin Risk
Assessment?
IDL No Yes No No
EDL1 No Yes Yes Yes
MDL / DL No Yes No No
LOD2 No Yes Yes Yes
PQL Yes Yes No No
RL / QL / SQL / LOQ Yes Yes Yes Yes1Specific to dioxins/furans2Specific to DoD projects 24
RLs most reliable value (aka LOQ, QL, SQL, ML, CRQL) Most labs RLs 2-10 ng/L, depending on PFAS Do not use MDLs as nondetect values No J values
What To Use for PFAS?
PFBA: 0.35 J ng/L PFBA: <2.0 ng/L PFBA: 2.5 ng/L25
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Typical sample result summary form
Number of PFAS reported
Results, RLs, units
Dilution results
Collection date, prepared date, analysis date
Percent solids (dry weight)
Isotope Dilution recoveries
PFAS Analytical Reports
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CAS Numbers and PFAS State
PFAS State Structure CAS No.
PFOAAnion Perfluorooctanoate C7F15CO2
- 45285-51-6
Acid Perfluorooctanoic acid C7F15COOH 335-67-1
PFOSAnion Perfluorooctane sulfonate C8F17SO3
- 45298-90-6
Acid Perfluorooctane sulfonic acid C8F17SO3H 1763-23-1
Labs should report acid form and CAS No. for acid
DoD 5.1 vs 5.2
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Standardized Methods in the Future?
Future Method Matrix Calibration Analytes/RLs When?
SW-846 8327 Aqueous(non-DW)
Direct injection; External standard
24 PFAS;RL 10 ng/L
Out for public comment soon
SW-846 8328 Aqueous and solids Isotope dilution
24 PFAS in 8327 plus Gen-X; RL 10 ng/L
Spring 2019; EPA
collaborating with DoD
SW-846 8329 Solid prep method NA NA Not definite
New Drinking Water Method Drinking Water SPE; Internal
standardShorter chain
PFASJune 2019; EPA ORD &
Office of Water
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Summary – Take Away Points
No standard PFAS Analytical Method for non-DW matrix
SOPs are inconsistent across laboratories
Differences between DoD QSM 5.1 and 5.2
Evaluate the reported QC results
Understand what your lab’s procedures are
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Questions?Elizabeth Denly, ASQ CMQ/OEP: (978) 656-3577 | E: [email protected]