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Method Development Studies for Method Development Studies for Hexavalent Chromium in Ambient Hexavalent Chromium in Ambient
Air SamplesAir Samples
Julie L. Swift
Eastern Research Group, Inc.
1
Introduction
� History of EPA Hexavalent Chromium (Cr(VI) Method)
http://www.epa.gov/ttnamti1/files/ambient/airtox/hexchro
msop.pdf
� Analytical preparation method change
� Improvements in precision after method change
� Evaluation of EPA Method vs. other analytical techniques (IC/UV vs. IC/ICPMS)
� Evaluation of EPA/NATTS sampler vs. sampler developed by NYS and Clarkson University
2
2003 - ERG started working on method
2004 - EPA contracted ERG to study CARB 039
method
- ERG authored Method Development paper
2006 - ERG authored an SOP
(http://www.epa.gov/ttnamti1/airtox.html)
2008 - ERG modified NATTS sampler to add chiller
2009 - ERG modified filter preparation technique before
sampling – stable <15°C (60°F) for 3 days
2011 - ERG modified sample preparation technique –
sonication vs. shaking
2012 - New study with NJ DEP CTI Grant3
Timeline of EPA Method Variations
� Incorporated analytical procedure to obtain lowest Method Detection Limits (MDL)
� Investigated filter media
– Cellulose, Binderless Quartz, PVC, Teflon
– Cellulose showed best retention but had high
background – had to acid wash in order to obtain low
MDL (current MDL = 0.0034 ng/mL)
� Investigated interferences
– No interference of Cr (III), Fe, Mg
4
ERG Initial Study (2003-2004)
� Added chiller to keep samples frozen while sampling and up to 3 days after sampling
– Works in laboratory conditions, but collects water at sites with high humidity/high temperature
� ERG modified filter preparation technique before sampling – stable for up to 3 days at <15°C (60°F)
5
ERG Sampler Study: Chiller (2008-2009)
T o
A t m o s p h e r e
F l o w
C o n t r o l
V a l v e
S a m p le
F l o w
R o t a m e t e r
S a m p le
P u m p
O U T S I D E
I N S I D E
F i l t e rH o l d e r
F u n n e lA s s e m b l y
F i l t e r
F i l t e rH o l d e r
F u n n e lA s s e m b l y
F i l t e r
S a m p l e A i r i n F r o m A t m o s p h e r e
C h i l l e r
ERG Sampler Study: Chiller (2008-2009)
6
Sample Air in From Atmosphere
OutsideInside
ChillerSample Pump
Sample
Flow
Rotameter
To Atmosphere
Flow Control
Valve
0
10
20
30
40
50
60
70
80
90
100
Day 0 Day 1 Day 3 Day 5
NATTS Chiller, 15°C Chiller,18°C Chiller, 21°C7
ERG Sampler Study: Chiller (2008-2009)
% R
ecovery
� Community Toxics Initiative Grant
– NJ DEP CTI grant (funds from US EPA)• Dr. Linda Bonanno – Principal Investigator at NJDEP
“Evaluation of Two Analytical Methods and Sampling
Trains for the Measurement of Hexavalent Chromium in
Ambient Air”
– In conjunction with University of Medicine and Dentistry of NJ (EOHSI), Clarkson University and ERG
• Compare Analytical Instrumentation
– IC/UV
– IC/ICPMS
• Compare Sampling Systems (added ERG Prototype)
– EPA/NATTS Sampler
– Clarkson/State of NY
– ERG Prototype8
NJ DEP CTI: Newest Study (2009 - present)
Preliminary/Draft
� New Jersey Department of Environmental Protection:
– Dr. Linda Bonanno
� Clarkson University:
– Dr. Philip Hopke, Dr. Lin Lin, Mehdi Amouei
Torkmahalleh
� EOHSI:
– Dr. Tina Fan, Chang Ho Yu
� ERG:
– Julie Swift, Victoria Genther, Dr. Laura Krnavek, Randy
Mercurio, Ariel Atkinson, Donna Tedder9
NJ DEP CTI:Research Team
Preliminary/Draft
� Evaluate the 2 analytical methods
– All cellulose filters are prepared at ERG
– Spiked filters were prepared by EOHSI and sent to
Clarkson, ERG and kept in-house
– Presented at 2011 National Air Toxics Monitoring &
Data Analysis Workshop
http://www.epa.gov/ttn/amtic/airtox-daw-2011.html
10
NJ DEP CTI: New Study Analytical Module Objective
Preliminary/Draft
NJ DEP CTI: Sample Preparation Changes
� Previously prepared samples for analysis by sonicating filters in sodium bicarbonate solution
– Studies with NJDEP/EOHSI/Clarkson have detected
Cr(VI) when Cr(III) was spiked on filters
– In previous ERG studies, we did not see this problem
– However, spiking concentration in new study is higher
• Recoveries showed need to reevaluate the preparation procedure
• Dr. Phil Hopke suggested that the presence of hydroxyl ions may cause conversion of Cr(III) to Cr(VI) during sonication
11 Preliminary/Draft
� If sonication is causing a problem, how should samples be prepared?
� Study sample extraction via sonication versus wrist-action shaker
� Data collected comparing sonication to shaking with liquid-spiked filters
– Cr(III) only
– Cr(VI) only
– Cr(VI) and Cr(III)
12
ERG Study:Sonicator vs. Shaker
0%
1%
2%
3%
4%
5%
15 30 45 60 75
Pe
rce
nt
rec
ove
ry,
Cr6
+
Time / minutes
Sonic Cr(III) / 1.10 ng/mL Shake Cr(III) / 1.10 ng/mL
ERG Study Sonicator vs. Shaker: Cr(III) only
13 Note: All recoveries for the shaker were zero.
80%
85%
90%
95%
100%
105%
110%
115%
120%
125%
130%
135%
140%
145%
150%
15 30 45 60 75
% R
eco
very
Time / minutes
Sonic Cr(VI) / 0.05 Sonic Cr(VI) / 0.1 Shake Cr(VI) / 0.05 Shake Cr(VI) / 0.1
ERG Study Sonicator vs. Shaker: Cr(VI) only
(ng/mL Cr6+)
14
ERG Study Sonicator vs. Shaker: Cr(III) and Cr(VI)
80%
90%
100%
110%
120%
130%
140%
150%
160%
170%
180%
190%
200%
15 30 45 60 75
% R
eco
very
Time (minutes)
Sonic O / 0.05 Sonic O / 0.1 Shake O / 0.05 Shake O / 0.1
(ng/mL Cr6+)
15
ERG Study Sonicator vs. Shaker: Increased Precision
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
2002 2003 2005 2006 2007 2008 2009 2010 2011 son 2011 shake
143 182 140 115 118 113
% R
PD
66
45
Maximum values for %RPD are in blue16
� Detected Cr(VI) on filters spiked with high levels of Cr(III) extracted via sonication
� Found that filters spiked with both Cr(III) and Cr(VI) extracted via shaking show acceptable recoveries and variability
� Duplicate filters extracted via shaker show good %RPD
� Changed extraction method to shaking for 45 minutes instead of sonicating for one hour
ERG Study Sonicator vs. Shaker: Conclusions
17
� Compared the IC/UV to IC/ICP-MS
– Standard NATTS method uses IC/UV
– New method uses IC/ICP-MS
� IC/ICP-MS method uses same filter as IC/UV (Sodium bicarbonate coated cellulose filters)
– Coated after acid washed, clean enough for low
concentration ambient samples
– Causes background on IC/ICP-MS for Cr(VI)
– Sodium Bicarbonate causes Cr(III) to precipitate (only
able to detect Cr(VI), not Cr(III) and Cr(VI) on
IC/ICPMS)
18
NJ DEP CTI: Analytical Instrumentation
Preliminary/Draft
NJ DEP CTI: Initial Laboratory Comparisons
� Audits were put in place in order to confidently evaluate the different analytical techniques
– External audits obtained by Wibby Environmental
– Internal audits prepared by ERG
� Method Detection Limits were preformed on each analytical system.
– IC/UV lower than IC/ICPMS (background interference
on IC/ICPMS does not allow lower MDL)
– ERG IC/UV results 3-4 times lower
� Laboratory techniques improved over time
19 Preliminary/Draft
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
EOSHI IC/ICPMS Clarkson IC/ICPMS EOSHI IC Clarkson IC ERG IC
low high low w/Cr3+ high w/Cr3+
NJ DEP CTI:Wibby Audit (August 2011)
Perc
ent
Recovery
20 Preliminary/Draft
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
EOSHI IC/ICPMS Clarkson IC/ICPMS EOSHI IC Clarkson IC ERG IC
low high low w/Cr3+ high w/Cr3
NJ DEP CTI:ERG Audit (September 2011)
Perc
ent
Recovery
21 Preliminary/Draft
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
EOSHI IC/ICPMS Clarkson IC/ICPMS EOSHI IC Clarkson IC ERG IC
low high low w/Cr3+ high w/Cr3
NJ DEP CTI:ERG Audit (October 2011)
Perc
ent
Recovery
22 Preliminary/Draft
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
EOSHI IC/ICPMS Clarkson IC/ICPMS EOSHI IC Clarkson IC ERG IC
low high
NJ DEP CTI:ERG Audit (January 2012)
Perc
ent
Recovery
23 Preliminary/Draft
� Sampler set up– Sampler installation – 6 samplers (8 ports)
• Plus ERG Prototype sampler
– Instrument design challenges
• Clarkson sampler also had water on filters but was a sampler error and was easily corrected
• ERG prototype collected water and was removed from study
� Not enough valid samples but did get some information– Use only Teflon screens in samplers (Clarkson)
– Tighten all filter holders (NATTS)
24
NJ DEP CTI:Summer 2011 Field Results
Preliminary/Draft
� All samples taken were sent to each laboratory– Each set included 8 samples
• 2 NATTS samplers – each sampler able to sample primary and collocated
• 4 Clarkson samplers – for study, 2 considered primary, 2 considered collocated
– Two whole sets sent to each laboratory
• EOHSI and Clarkson analyzed by IC/UV and IC/ICPMS
• ERG analyzed by IC/UV only
– Two sets sent to all 3 laboratories
• EOHSI analyzed by IC/UV and IC/ICPMS
• Clarkson and ERG analyzed by IC/UV only
26
NJ DEP CTI:Winter 2012 Field Results
Preliminary/Draft
� Only the IC/ICPMS & IC/UV final Cr(VI) results can be compared
� At this point, have not been able to compare the interconversion of Cr(VI)/Cr(III) by IC/ICPMS and IC/UV– Different sample preparation techniques used
• IC/ICPMS – acidified Nitric Acid extraction before analysis
• IC/UV – basic Sodium Bicarbonate extraction before analysis
� Blanks – IC/ICPMS appear to have interferences at low levels with the sodium bicarbonate filters – Could this be a problem for IC/ICPMS for low concentration
samples?27
NJ DEP CTI: Field Results - Discussion
Preliminary/Draft
� EPA Approved Cr(VI) Method developed by ERG was approved as an ASTM International Standard– Began process in 2008
– Modified draft in 2011 to incorporate new preparation technique (shaker instead of sonicator)
– Received approval on May 7, 2012!
Standard Test Method for
Determination of Total Suspended Particulate (TSP) Hexavalent Chromium in Ambient Air Analyzed By Ion Chromatography (IC) and SpectrophotometricMeasurements
28
ERG Recent Development (2012)
Conclusions
� ERG Prototype sampler collects water in humid/rainy conditions. It does give good recoveries for samples left out for multiple days
� Shaker converts less Cr(III) to Cr(VI) for spiked filters that contain Cr(III) over time
� More studies are needed to compare Clarkson and NATTS sampler Cr(VI) recoveries– Summer study not conclusive – too many variables
but did learn from it
– Winter study had low concentrations. Need more samples to obtain any definitive conclusions
� Now have a ASTM Cr(VI) method29 Preliminary/Draft
Acknowledgements
� The Community Toxics Initiative Grant was funded in part by the US Environmental Protection Agency through a grant to the New Jersey Department of Environmental Protection
� We would like to thank the following people at U.S. EPA:
– David Shelow, Mike Jones, Joann Rice, Dennis Mikel
30