www.LancasterLabsEnv.com A Technique for Determining Total Oxidizable Precursors (TOP) of Perfluoroalkyl Compounds Providing comprehensive scientific resources to environmental clients worldwide. Chuck Neslund, Technical Director, Eurofins Lancaster Laboratories Environmental, LLC NEMC, Washington, DC August 7-11, 2017
24
Embed
A Technique for Determining Total Oxidizable …apps.nelac-institute.org/nemc/2017/docs/pdf/Tuesday...Providing comprehensive scientific resources to ... •Breathable waterproof fabrics
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
www.LancasterLabsEnv.com
A Technique for Determining Total Oxidizable Precursors (TOP) of Perfluoroalkyl Compounds
Providing comprehensive scientific resources to environmental clients worldwide.
If we wanted to assess the total potential impact of PFAS contamination, how would we approach given the fact that we only have analytical standards available for a small fraction of the potential contaminants present?
i. Captures fluorine at surfaceii. Sensitivity around 2-5 ug/l
b. AOF/CIC – Absorbable Organic Fluorine/Combustion Ion Chromatographyi. Sensitivity around 1 ug/l
10
Total Oxidizable Precursors - TOP
Concept is to analyze a sample for perfluoroalkyl carboxylic acids (PFCA) and perfluoroalkyl sulfonic acids (PFSA) and any identified precursors . Then subject a second aliquot of the sample to relatively harsh oxidative conditions. Analyze the oxidized sample for the same perfluoroalkyl acids and precursors. Expect to see;
a. Reduction or elimination of the precursorsb. Increase in concentrations of perfluoroalkyl acids
11
TOP – Total Oxidizable Precursors
Based on paper authored by Erika Houtz and David Sedlak(ES&T, 2012, 46, 9342-9349)
Concept is to analyze a sample for perfluorinated acids and precursors (such as telomer sulfonates). Then subject a second aliquot of the sample to relatively harsh oxidative conditions. Analyze the oxidized sample for the same perfluorinated acids and precursors. Expect to see;
a. Reduction or elimination of the precursors
b. Increase in concentrations of perfluorinated acids
Future – TOP Analysis
12
TOP Assay
Houtz & Sedlak (2012),
ES&T, 9342-9349
• Compounds like fluorotelomer sulfonates, alcohols and sulfonamides
considered precursors
• Precursors have some part of organic structure that is susceptible to
oxidation, i.e. C-H bond
13
• Oxidation process for TOP Assay addresses those compounds that can be converted to PFCAs.
• Would appear to be little or no influence from other organofluorine compounds.
• Able to take advantage of LC/MS/MS analysis technique that uses isotope dilution.
• Sensitivity better that observed with PIGE and AOF/CIC. Limits in the low ng/l range.
TOP Assay – Advantage?
14
TOP Assay – Oxidation
• After analysis sample(s) by normal LC/MS/MS isotope dilution procedure, take second aliquot
• Spike sample with TOP oxidation appropriate QC• Add potassium persulfate and NaOH solutions to
aliquot of sample until potassium persulfate at 60mM and NaOH at 125 mM. Resulting pH should be approximately 13.
• 85C bath for 6 hours• Quench with HCl, adjust pH to approximately
neutral
15
Isotopically labeled compounds that are used with
extraction for LC/MS/MS monitor the extraction efficiency
for the PFAS analysis, but what about the TOP Assay?
• Procedural recovery standards – labeled PFAAs that are not
theoretically reactive to TOP Assay
13C2-PFHxA
13C2-PFOA13C4-PFUnDA
• Reaction Efficiency Standards – labeled PFAA precursor that should completely disappear when subjected to TOP Assay
13C2-4:2-FTS
d3-NMeFOSAA
TOP Assay - QC
16
Results – TOP Assay
0
200
400
600
800
1000
1200
1400
PF
BA
PF
PeA
PF
BS
RE
S-1
3C
2-4
:2-F
TS
4:2
-FT
S
PF
HxA
PF
PeS
PF
HxS
PF
HpA
6:2
-FT
S
PF
HpS
PF
OA
PF
OS
PF
NA
PF
OS
A
PF
NS
PF
DA
8:2
-FT
S
RE
S-d
3-N
MeF
OS
AA
NM
eF
OS
AA
PF
DS
PF
UnD
A
NE
tFO
SA
A
PF
DoD
A
10
:2-F
TS
PF
DoS
PF
TrD
A
PF
Te
DA
PF
HxD
A
PF
OD
A
No TOP Digest TOPSMP1A
No TOP Digest TOPSMP1B
TOPDIG1
TOPDIG2
TOPDIG3
TOPDIG4
17
Results – TOP Assay
0
200
400
600
800
1000
1200
1400
No TOP Digest TOPSMP1A
No TOP Digest TOPSMP1B
TOPDIG1
TOPDIG2
TOPDIG3
TOPDIG4
18
• Comparison of sample results from Pre-TOP versus Post-TOP when no precursors determined to be present indicates no artifacts added to sample