UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

 WASHINGTON D.C. 20460 

 

OFFICE OF THE ADMINISTRATOR 

 SCIENCE ADVISORY BOARD 

November 30, 2010 

EPA-CASAC-11-002 

The Honorable Lisa P. Jackson 

Administrator 

U.S. Environmental Protection Agency 

1200 Pennsylvania Avenue, N.W. 

Washington, D.C. 20460 

Subject: CASAC Review of EPA’s White Paper, “Approach for the Development of a 

New Federal Reference Method (FRM) for Lead in Total Suspended 

Particulates (Pb-TSP)” 

Dear Administrator Jackson: 

 

 In November 2008, EPA published the final rule for the National Ambient Air Quality 

Standard (NAAQS) for lead, revising the primary standard by an order of magnitude, from 

1.5 μg/m3

 to 0.15 μg/m3 three-month average. The indicator for the Lead NAAQS, lead in total 

suspended particulates (Pb-TSP), did not change. There are a variety of air monitoring methods 

that can measure ambient lead concentrations. A Federal Reference Method (FRM) is a 

monitoring method designated by EPA that meets specific requirements for adequacy to 

demonstrate attainment of the NAAQS. As a result of the lowering of the Lead NAAQS and 

improvements in analytical measurement technologies, EPA is considering developing a new 

FRM for Pb-TSP. This is outlined in EPA’s white paper, Approach for the Development of a 

New Federal Reference Method (FRM) for Lead in Total Suspended Particulates (Pb-TSP). 

EPA requested that the Ambient Air Monitoring and Methods Subcommittee (AAMMS, or the 

Subcommittee) of the Clean Air Scientific Advisory Committee (CASAC) provide a peer review 

of the white paper. As part of the peer review, the Subcommittee held a public teleconference on 

September 15, 2010 and prepared comments in response to EPA’s four charge questions, which 

centered on extraction methods, analytical methods, validation and testing, and inter-laboratory 

variability. The Chartered CASAC approved this letter during a teleconference on November 8, 

2010. The CASAC and AAMMS memberships are listed in Enclosure A. CASAC’s consensus 

responses to the Agency’s charge questions are presented in Enclosure B. Individual review 

comments from the AAMMS are compiled in Enclosure C. Major highlights of the report are 

presented below.

 

EPA’s white paper presents a proposed new Pb-TSP FRM consisting of two extraction 

methods, ultrasonic bath with a nitric acid/hydrochloric acid solution and hot block reflux with 

nitric acid, followed by analysis using inductively coupled plasma-mass spectrometry (ICP-MS). 
2 

CASAC finds that the two extraction methods as well as ICP-MS are appropriate. However, 

CASAC recommends a strategy that provides flexibility to use additional, applicable extraction 

methods (e.g. microwave digestion) and analytical measurement methods (e.g. Graphite Furnace 

Atomic Absorption Spectroscopy), including those used as parts of the current FRM. As 

previously recommended, EPA should consider developing performance-based FRMs. 

EPA’s white paper also presents an approach for intra-laboratory and inter-laboratory 

validation and testing. CASAC finds that the criteria set forth for intra-laboratory validation 

needs to be strengthened. CASAC views the comprehensiveness of the planned inter-laboratory 

testing as at an appropriate level, but recommends that EPA consider separating the extraction 

methods from the analytical methods so that any of the acceptable extraction methods can be 

used with any of the acceptable analytical measurement methods. CASAC does not recommend 

a specific level of acceptable inter-laboratory variability, but recommends identifying and taking 

into consideration the data quality objectives of the overall measurement. 

Although EPA’s white paper is specific for Pb-TSP as the indicator, CASAC reiterates 

prior recommendations that EPA consider moving away from using Pb-TSP as the indicator and 

consider using lead in PM10 (Pb-PM10) as the indicator. Measuring Pb-TSP involves the use of 

high-volume TSP sampling devices, whereas measuring Pb-PM10 involves the use of lowvolume PM10 sampling devices. Low-volume Pb-PM10 sampling has several advantages over 

high-volume Pb-TSP sampling, including the widespread use of such sampling and the ability to 

measure multiple compounds in addition to lead. Field studies should be conducted with an 

appropriate experimental design to assess low-volume Pb-PM10 sampling, making comparison to 

high-volume Pb-TSP sampling, to develop data for considering Pb-PM10 as the indicator in 

future Pb NAAQS reviews. If the Agency determines that Pb-PM10 is not appropriate as an 

indicator, CASAC encourages the development of a more robust particle sampler for TSP, such 

as low-volume TSP sampling that would allow the use of alternative filter substrates to those 

currently used in high-volume TSP samplers. 

 

 CASAC appreciates the opportunity to provide advice on this issue and looks forward to 

receiving the Agency’s response. 

Sincerely, 

 /Signed/ /Signed/ 

Dr. Armistead (Ted) Russell, Chair Dr. Jonathan M. Samet, Chair 

CASAC AAMM Subcommittee Clean Air Scientific Advisory Committee 

Enclosures
NOTICE 

This report has been written as part of the activities of the EPA's Clean Air Scientific 

Advisory Committee (CASAC), a federal advisory committee independently chartered to 

provide extramural scientific information and advice to the Administrator and other officials of 

the EPA. CASAC provides balanced, expert assessment of scientific matters related to issues 

and problems facing the Agency. This report has not been reviewed for approval by the Agency 

and, hence, the contents of this report do not necessarily represent the views and policies of the 

EPA, nor of other agencies within the Executive Branch of the federal government. In addition, 

any mention of trade names or commercial products does not constitute a recommendation for 

use. CASAC reports are posted on the EPA Web site at: http://www.epa.gov/casac. 

3 
Enclosure A – Rosters 

U.S. Environmental Protection Agency 

Clean Air Scientific Advisory Committee (CASAC) 

Ambient Air Monitoring and Methods Subcommittee (AAMMS)

CHAIR 

Dr. Armistead (Ted) Russell, Professor, Department of Civil and Environmental Engineering, 

Georgia Institute of Technology, Atlanta, GA 

MEMBERS 

Mr. George A. Allen, Senior Scientist, Northeast States for Coordinated Air Use Management 

(NESCAUM), Boston, MA 

Dr. Judith Chow, Research Professor, Desert Research Institute, Air Resources Laboratory, 

University of Nevada, Reno, NV 

Mr. Bart Croes, Chief, Research Division, California Air Resources Board, Sacramento, CA 

Dr. Kenneth Demerjian, Professor and Director, Atmospheric Sciences Research Center, State 

University of New York, Albany, NY 

Dr. Delbert Eatough, Professor of Chemistry, Department of Chemistry and Biochemistry, 

Brigham Young University, Provo, UT 

Dr. Eric Edgerton*, President, Atmospheric Research & Analysis, Inc., Cary, NC 

Mr. Henry (Dirk) Felton, Research Scientist, Division of Air Resources, Bureau of Air Quality 

Surveillance, New York State Department of Environmental Conservation, Albany, NY 

Dr. Philip Hopke, Bayard D. Clarkson Distinguished Professor, Department of Chemical and 

Biomolecular Engineering, Clarkson University, Potsdam, NY 

Dr. Rudolf Husar, Professor, Mechanical Engineering, Engineering and Applied Science, 

Washington University, St. Louis, MO 

Dr. Kazuhiko Ito*, Assistant Professor, Department of Environmental Medicine, School of 

Medicine, New York University, Tuxedo, NY 

Dr. Donna Kenski*, Data Analysis Director, Lake Michigan Air Directors Consortium, 

Rosemont, IL 

Dr. Thomas Lumley*, Associate Professor, Biostatistics, School of Public Health and 

Community Medicine, University of Washington, Seattle , WA 

4 
Dr. Peter H. McMurry, Professor, Department of Mechanical Engineering, University of 

Minnesota, Minneapolis, MN 

Mr. Richard L. Poirot, Environmental Analyst, Air Pollution Control Division, Department of 

Environmental Conservation, Vermont Agency of Natural Resources, Waterbury, VT 

Dr. Kimberly A. Prather*, Professor, Department of Chemistry and Biochemistry, University 

of California, San Diego, La Jolla, CA 

Dr. Jay Turner, Associate Professor, Environmental & Chemical Engineering, Campus Box 

1180 , Washington University , St Louis, MO 

Dr. Warren H. White, Research Professor, Crocker Nuclear Laboratory, University of 

California - Davis, Davis, CA 

Dr. Yousheng Zeng, Air Quality Services Director, Providence Engineering & Environmental 

Group LLC, Baton Rouge, LA 

Dr. Barbara Zielinska*, Research Professor, Division of Atmospheric Sciences, Desert 

Research Institute, Reno, NV 

SCIENCE ADVISORY BOARD STAFF 

Mr. Aaron Yeow, Designated Federal Officer, U.S. Environmental Protection Agency, 

Washington, DC 

* Did not participate in the review 

5 
6 

U.S. Environmental Protection Agency 

Clean Air Scientific Advisory Committee (CASAC) 

CHAIR 

Dr. Jonathan M. Samet, Professor and Flora L. Thornton Chair, Department of Preventive 

Medicine, University of Southern California, Los Angeles, CA 

MEMBERS 

Mr. George A. Allen, Senior Scientist, Northeast States for Coordinated Air Use Management 

(NESCAUM), Boston, MA 

Dr. Joseph D. Brain, Cecil K. and Philip Drinker Professor of Environmental Physiology, 

Department of Environmental Health, Harvard School of Public Health, Harvard University, 

Boston, MA 

Dr. H. Christopher Frey, Professor, Department of Civil, Construction and Environmental 

Engineering, College of Engineering, North Carolina State University, Raleigh, NC 

Dr. Armistead (Ted) Russell, Professor, Department of Civil and Environmental Engineering, 

Georgia Institute of Technology, Atlanta, GA 

Dr. Helen Suh, Senior Lecturer on Environmental Chemistry and Exposure Assessment, 

Department of Environmental Health, School of Public Health, Harvard University, Boston, MA 

Dr. Kathleen Weathers, Senior Scientist, Cary Institute of Ecosystem Studies, Millbrook, NY 

SCIENCE ADVISORY BOARD STAFF 

Dr. Holly Stallworth, Designated Federal Officer, U.S. Environmental Protection Agency, 

Washington, DC 
Enclosure B 

Consensus Responses to Charge Questions on EPA’s White Paper, Approach for the 

Development of a New Federal Reference Method (FRM) for Lead in Total Suspended 

Particulates (Pb-TSP)

1. What are the Panel’s views on the two extraction method options of heated ultrasonic and 

graphitic hot block with nitric/hydrochloric acid for the extraction of Pb from TSP? 

EPA is proposing to replace the current extraction method described in Appendix G of 40 

CFR Part 50 with one of the two methods listed above. The major aspects of the three methods 

are compared in the following Table. From a chemical extraction point of view, the three 

methods should be nearly equivalent for the extraction of Pb from particles collected on either a 

glass or quartz fiber filter. As pointed out in the white paper, the hydrochloric acid added to the 

Ultrasonic Bath technique will assist in the extraction of more refractory metals from the sample, 

but is not needed for the recovery of Pb. 

Method Current Method Ultrasonic Bath Hot Block Reflux 

Fraction Analyzed 3⁄4” x 8” strip 3⁄4” x 8” strip 3⁄4” x 8” strip 

Solution 15 mL, 3 M HNO3 15 mL, 1 M HNO3, 

2 M HCl 

20 mL, 1:19 v/v 

HNO3

Extraction 30 min, boiling 60 min, 80 oC 60 min, 95 oC 

Although many versions of the traditional extraction approach using heated ultrasonic 

water bath with nitric/hydrochloric acids have been used successfully, they do not represent the 

current state-of-art extraction approaches (e.g., microwave digestion). Compendium Method IO3.1 (USEPA, 1999a) describes a validated microwave digestion method that EPA originally 

developed in 1989. Qureshi, et al. (2006) describe a more contemporary approach to microwave 

digestion. A survey of the recent literature should permit an easy update of EPA’s Compendium 

Method IO-3.1. Thus, it would be straightforward to incorporate microwave digestion in the 

intercomparison tests and determine its equivalence to the other proposed methods. It has the 

advantage of handling a greater sample throughput with the potential for reduced sample-tosample variability, given the features of current generation microwave digestion systems. Thus, 

the Subcommittee recommends moving forward with the ultrasonic bath and hot block reflux 

methods, but adding microwave digestion as an additional option. Given the variety of potential 

methods available which appear to perform well, another approach would be to develop 

performance-based standards (quantification of extraction efficiency) to define acceptable 

extraction procedures for the FRM. 

2. What are the Panel’s views on ICP-MS as the analysis method for Pb-TSP? 

The Subcommittee views that inductively coupled plasma-mass spectrometry (ICP-MS) 

is an appropriate analytical method for the Pb-TSP FRM. ICP-MS has superior sensitivity and 

specificity for Pb, which is a key criterion for the FRM. Furthermore, the method can generate 

data for multiple elements and, depending on the sensitivity of the instrument, can generate data 

7 
for the isotopic composition of Pb, which can provide insight into source attribution. Many 

state/local agencies are already operating ICP-MS instruments, as demonstrated by the data 

reported to EPA for PM10 air toxics metals (including Pb) under the National Air Toxics Trends 

Stations (NATTS) program. 

There are advantages to designating a single analytical method as the FRM, especially if 

it has sufficiently high performance that it would remain a suitable method, should revisions be 

made to the Pb NAAQS. That said, the Subcommittee recommends a strategy that provides 

flexibility, such that agencies can use other methods such as Graphite Furnace Atomic 

Absorption Spectrometry (GFAAS), if they are deemed suitable. One approach would be to 

designate a performance-based FRM, which would define key performance criteria for minimum 

detection limit (MDL), precision, accuracy, linearity, and tolerance for interference. An FRM 

based solely on performance, however, has the drawback that each monitoring agency would 

have to demonstrate the ability to meet these performance criteria, which could be burdensome. 

Alternatively, a single analytical method could be designated as the FRM and performance 

criteria could be defined to serve as the basis for Federal Equivalent Method (FEM) designations. 

In this case, the Subcommittee strongly recommends that the proposed evaluation of candidate 

FRM methods also include analytical methods beyond ICP-MS (including, but perhaps not 

limited to, GFAAS) with the intent that methods meeting the performance criteria would be 

directly designated as an FEM. In effect, EPA would have completed the FEM process for any 

monitoring agencies that would like to use these qualified methods. This approach should be 

more cost effective and provide a high level of consistency because all candidate methods are 

evaluated by the same labs using the same procedures. 

The Subcommittee also recommends that EPA consider: 

• Evaluating and possibly designating as an FRM or FEM commonly used ICP-MS 

based analytical methods, such as EPA Compendium Method IO-3.5 (USEPA, 

1999b) which is already used by many monitoring agencies for NATTS sample 

analysis. 

• Including low-volume PM10 samples collected on Teflon filters with analysis by XRay Fluorescence (XRF) as part of the candidate FRM testing. While this advisory 

response focuses on the Pb-TSP method, EPA promulgated an FRM for the 

determination of Pb in PM10 (CFR, Appendix Q to Part 50) and in the future may 

consider the feasibility of low-volume TSP sampling. 

• Including the current FRM analytical method (GFAAS) in the evaluation of candidate 

FRM methods to assess comparability and help bridge past and future data. 

• Including the analysis of other elements in the candidate FRM tests. Since the 

monitoring agencies would be able to analyze for multiple elements at a small 

incremental cost (at least for methods such as ICP-MS), the documentation of method 

performance for multiple elements would assist the agencies in prudent use of such 

data for air toxics, studies, source apportionment, etc. However, it should be noted 

that the high-volume TSP method (sampler and filter media) are less suitable for 

other metals than a PM10 Teflon filter sample due to the limitations inherent in the 

TSP sampler as well as potential limitations of TSP filter media for trace metal 

analysis. 

8 
3. What are the Panel’s views on the approach described for evaluating and testing the method 

prior to proposal as a new FRM for Pb-TSP? 

 The overall approach to validation and testing needs to include a comparison to the 

existing extraction and analytical methods. A satisfactory comparison to the existing methods 

will ensure that the data collected using a new FRM will be consistent with the older Pb database. 

This is not likely to be an issue, but it is good practice and should prevent any unexpected 

changes in the resultant dataset. 

The test matrix, as outlined in the white paper, sets a low bar for validation of the 

proposed methods for extraction and analysis of Pb from glass and quartz fiber filters. It also 

does not include enough detail on issues such as how the spiked samples will be prepared, which 

lab will determine the accuracy and precision of the spiked samples, and whether the sampled 

filters will include potential interferences (such as heavy and light loadings of metals, and other 

pollutants such as elemental carbon). To address these issues, the test protocol should include a 

description of how the test strips are prepared and include an analysis of a subset of the prepared 

strips by an acceptable reference laboratory. The selection process for the sampled filters should 

be more clearly specified and should include some potential interferents for the extraction and 

analytical processes. Archived filters are available and it is likely that state and local monitoring 

agencies can assist with the selection of appropriate filters. 

EPA has based the development of the Pb analytical FRM on the Office of Solid Waste’s 

SW-846 Method 6020A (USEPA, 2007). This method does not have adequate Quality 

Assurance for analysis of samples used in a compliance oriented air monitoring network. The 

following recommendations address some of the criteria that are specified in the test matrix in 

the white paper, but need to be strengthened for a Pb FRM. 

• The Low Level Calibration Verification (LLCV ) should be ± 10%. 

• The Low Level Quality Control Sample (LLQC ) is not really that low since it is 30% 

of the NAAQS. The recovery limits should be at minimum ± 15%. 

• The recoveries of Standard Reference Material (SRM) spiked on unexposed filter 

strips at all concentrations should be ± 10%. 

• The 3 non-sequential results should not be averaged in the bias calculation. This will 

not provide an indication of single sample bias, which is how actual samples are 

analyzed. In general ± 10% bias is too loose, but 5% may be too stringent. A 

precision of 10% seems reasonable, because it includes the uncertainty due to 

potentially uneven loadings from sampled filters. 

• The replicate analysis, as specified in EPA 6020A, only requires one replicate 

analysis per batch. The batch size must be specified in the method since new 

extractors can accommodate up to 96 samples. One replicate for every 20 samples 

should be considered to be a minimum. 

The Pb FRM development program should include Teflon filter media, as well as an 

accommodation for the analysis of other pertinent elements for air toxics and source attribution 

work. This will not conflict with the TSP Pb FRM field sampler since the extraction and 

analytical portion of the FRM can be separated from the sample collection method. It may be 

9 
appropriate to constrain evaluation of the high-volume TSP sampler filter extraction process to 

Pb, since most air agencies would presumably use the PM10 FRM with Teflon filters for other 

metals analysis. Teflon filters from a PM10 FRM are more suitable for trace metal analysis than 

the quartz or glass fiber media needed for TSP samplers because of fewer contamination issues. 

Teflon filters can also be used for XRF analysis, a cost effective approach for analysis of 

multiple elements. 

4. Inter-laboratory testing of the method will be done to assess between-laboratory variability 

(CV) at the 95% confidence interval. What are the Panel’s views on a reasonable level on 

inter-laboratory variability? 

The Subcommittee is generally comfortable with the comprehensiveness of the planned 

inter-laboratory testing. A full array of laboratory and extraction method comparisons will be 

performed using spiked and archived sample filter strips. The results will be analyzed to 

distinguish the components of variance attributable to intra-laboratory precision and interlaboratory bias. The Subcommittee believes that the existing Federal Reference Method for 

extraction and analysis should be added to the experimental design to support quantitative 

comparisons between new and historical data. 

The Subcommittee urges the Agency to consider decoupling the tests of extraction and 

analysis, as is recommended by EPA’s methods development and validation guidance (USEPA, 

1992) cited in the white paper. Extraction and analysis could be distinguished by collecting 

different laboratories’ extracts for analysis by a single operator on a single instrument, and 

sending extracts prepared by a single operator to different laboratories for analysis. The 

procedure-resolved results would allow future consideration of alternative method combinations. 

On the specific question of “a reasonable level of inter-laboratory variability”, the 

theoretical implications of target bias and precision values are discussed in the individual 

comments by Dr. Warren White. The Subcommittee does not recommend a specific level, but 

rather recommends identifying and taking into consideration the data quality objectives of the 

overall measurement. 

References: 

Qureshi, S., Dutkiewicz, V.A., Khan, A.R., Swami, K., Yang, K.X., Husain, L., Schwab, J.J., 

Demerjian, K.L., 2006. Elemental composition of PM2.5 aerosols in Queens, New York: 

Solubility and temporal trends. Atmospheric Environment, 40, S238–S251. 

USEPA, 1992. Development and Validation of SW-846 Methods Phase 2: Formal Validation. In 

Guidance for the Methods Development and Methods Validation for the RCRA Program, 

Washington, DC. 

10 
11 

USEPA. 1999a. Compendium Method IO-3.1, Selection, Preparation and Extraction of 

Filter Material. In Compendium of Methods for the Determination of Inorganic Compounds in 

Ambient Air, EPA/625/R-96/010a, Cincinnati, OH. 

USEPA. 1999b. Compendium Method IO-3.5, Determination of Metals in Ambient Particulate Matter 

Using Inductively Coupled Plasma/Mass Spectrometry (ICP/MS). In Compendium of Methods for the 

Determination of Inorganic Compounds in Ambient Air, EPA/625/R-96/010a, Cincinnati, OH. 

USEPA, 2007. Method 6020A, Inductively Coupled Plasma-Mass Spectroscopy. In Test 

Methods for Evaluating Solid Waste, Physical/Chemical Methods (SW-846), Washington, DC.
Enclosure C 

Compendium of Individual CASAC AAMMS Comments on EPA’s White Paper, Approach 

for the Development of a New Federal Reference Method (FRM) for Lead in Total Suspended 

Particulates (Pb-TSP) 

Comments from Mr. George A. Allen....................................................................................... 13

Comments from Dr. Judith Chow............................................................................................. 15

Comments from Mr. Bart Croes ............................................................................................... 19

Comments from Dr. Kenneth Demerjian................................................................................. 21

Comments from Dr. Delbert J. Eatough................................................................................... 22

Comments from Mr. Dirk Felton .............................................................................................. 26

Comments from Dr. Philip Hopke ............................................................................................ 29

Comments from Dr. Jay Turner................................................................................................ 30

Comments from Dr. Warren White .......................................................................................... 33

12 
Comments from Mr. George A. Allen 

General background

This charge to the AAMMS does not include the sample collection method for the Pb 

FRM -- that remains the Hi-Volume sampler with quartz or glass-fiber filters at this time. The 

issues discussed here are related to analysis of these filters for Pb and related issues, in the 

context of revising the Pb FRM’s analytical method to better suit the new and much (10 times) 

lower PB NAAQS that is now in effect. As EPA notes, this large drop in the NAAQS requires 

revision of the analytical method to insure that data of high quality can be reported at these much 

lower concentration loadings on the FRM Hi-Vol filter. These lower loadings require assessment 

of both the filter extraction process and the analysis method used for the Pb FRM. Analytical 

methods have also changed dramatically since the Pb FRM was last revised; this process allows 

the FRM to be updated to take advantage of these newer technologies. 

It is important to note that for these components of the Pb FRM, there are likely to be 

FEM methods approved that may be more practical for routine use. Still, it is important to have a 

robust and well characterized FRM in place even though analysis of Pb from Hi-Vol filters by 

any reasonable method with sufficient sensitivity is probably much more robust than the 

uncertainties inherent in the existing Pb FRM Hi-Vol sampling method. This process updates the 

“back end” of the method; I strongly encourage EPA to continue development of a “larger 

particle Lower-Vol” Pb FRM sampler that can provide accurate and reproducible samples to 

better harmonize the improvements in the Pb-FRM filter analysis being discussed here. 

Charge Question 1. “What are the panel’s views on the two extraction method options of heated 

ultrasonic and graphitic hot block with nitric/hydrochloric acid for the extraction of Pb from 

TSP?” 

Either extraction method should meet the needs of a revised Pb FRM, and both of these 

methods are currently approved by EPA as FEM methods for Pb extraction off a Hi-Vol filter. 

Assuming their performance is similar across the expected lower range of Pb filter loadings, I 

would recommend using the simpler method, which in this case appears to be the graphitic hot 

block with nitric acid, Method EQL-0710-192. It is worth noting here that a graphitic hot block 

may not be necessary; aluminum has been shown to work well and is a simpler approach. While 

the other method (sonication and both acids, EQL-0510-191) may be needed for extraction of 

other metals, it is not needed for Pb, and this is a Pb FRM, not an FRM intended for wider use. 

Sonication adds complexity to the method especially if “trace” analysis protocols are used; 

quartz fiber filters produces a “filter mush” that requires an extra step to remove the filter 

material from the liquid, usually with a centrifuge. Glass fiber filters may also need this 

treatment after sonication. 

13 
Charge Question 2. “What are the panel’s views on ICP-MS as the analysis method for PbTSP?” 

For the Pb-FRM, ICP-MS is clearly the preferred analysis technique. It is a highly 

sensitive and specific method for Pb; there are no other obvious candidate methods. 

Charge Question 3. “What are the panel’s views on the approach described for evaluating and 

testing the method prior to proposal as a new FRM for Pb-TSP? 

The described approach is rigorous. The description of the “archived” field (real 

samples?) filters needs to be clarified -- where are the samples from, what are the loadings, etc. 

This use of real samples for assessing extraction, especially at lower Pb loadings, is an important 

part of the evaluation since dry loading combined with a large amount of other material may 

effect the extraction process. The information in Table 1 (dry NIST SRMs) needs clarification. 

How will the dry SRM be applied to the filter? What does the “minimum weight” column mean? 

There is an assumption here that quartz filters would be used since they have lower blank 

levels for some metals of interest other than lead. But again, this is an FRM for Pb - not other 

metals - and glass fiber filter Pb blanks are very low. An agency would presumably use glass 

fiber filters for Pb since that media is much less fragile than quartz fiber filters. If other metals 

were of interest, I’d expect that they would be done using a low-volume PM10-FRM Teflon 

filter sampler, usually using either XRF and/or ICP-MS. I would not expect agencies to routinely 

do other metals off a Hi-Vol filter sample, and thus I would suggest that EPA simplify the Pb 

FRM evaluation by constraining tests to glass fiber filters. For (PM10) “trace metals”, the Hi-Vol 

sampler is not the sampling method or filter media of choice. Trace level analysis requires “trace 

level” protocols across the entire method, and a low-vol PM10 FRM Teflon sampling method is 

better suited for this. 

Charge Question 4. “Inter-laboratory testing of the method will be done to assess between 

laboratory variability (CV) at the 95% confidence interval. What are the panel’s views on a 

reasonable level of inter-laboratory variability? 

Inter-laboratory method testing is an important component of the FRM assessment, since 

it will better reflect the real-world performance of the method -- which is usually somewhat 

degraded from ideal testing conditions. For an acceptable level of inter-lab variability that 

includes variability from filter extractions, a starting point for this value might be the recovery 

range noted in the white paper: “The SRMs are expected to be recovered within 80 to 120% of 

the certified value per method 6020A”. If initial test results show a tighter recovery range, then 

the inter-lab criteria could be tightened. I would expect much of the inter-lab variability to be 

from the extraction process, since a well-controlled ICP-MS analysis for Pb should have 

reasonably tight inter-lab variability at these levels. 

14 
Comments from Dr. Judith Chow 

This memo addresses the four questions on which the Subcommittee members were 

asked to comment regarding “the White Paper on the Approach for the Development of a New 

Federal Reference Method (FRM) for Pb in Total Suspended Particulates (TSP).” This 

supplements prior comments to the first set of questions that was appended to the August 12, 

2008 letter from Dr. Russell to Administrator Johnson. 

Question 1: What are the panel’s views on the two extraction method options of heated 

ultrasonic and graphitic hot block with nitric/hydrochloric acid for the extraction of Pb from 

TSP? 

Both the heated ultrasonic water bath (with 1.02 M nitric acid [HNO3]/2.23 M 

hydrochloric acid [HCl]) and graphite hot block (with 3.5 % HNO3 [v/v] at 95 ± 5 °C) are 

adequate methods to extract PM deposits on glass-fiber or quartz-fiber filters. It is assumed that 

blank filters have been acceptance-tested to assure that Pb blank levels are negligible. However, 

the extraction method should be performance-based (e.g., Ashley et al., 1999; Oehme and Lund, 

1979) and not limited to the two most commonly used extraction methods defined in the white 

paper. For example, Moreira et al. (2005) showed that the microwave and the heating block 

digestion methods performed equally well for lead. 

The procedure for the heated ultrasonic HNO3/HCl method is more cumbersome and 

requires a centrifuge to complete the extraction. This method adds 15.0 ± 0.15 ml of the 

HNO3/HCl solvent to the filter aliquot, followed by 1 hr of ultrasonic extraction at 80 ± 5 °C in a 

loosely capped 50 ml extraction tube. After cooling, 25.0 ± 0.25 ml of distilled deionized water 

(DDW) are added to bring the volume to 40 ± 0.4 ml in a tightly capped extraction tube. This 

tube is then centrifuged for 20 minutes at 2500 RPM. Note that the water level in the ultrasonic 

bath also needs to be set above the level of the extraction solution in the tubes but below the 

level of the extraction tube caps to minimize contamination. Some of the solvent volume may be 

lost during the ultrasonic heating stage, because the caps are left loose. The use of HCl in the 

extract adds another potential source of contamination and produces a more complex analytical 

matrix; HNO3 by itself is an effective Pb solvent (U.S.EPA, 2007). 

The hot block digestion method is simple and straightforward. It involves transferring a 

20 ml aliquot of diluted HNO3 (1:19 v/v) from concentrated HNO3 (67 – 70%) to each extraction 

vessel, ensuring that the filter strip is covered with HNO3 extract, placing the vessel on the hot 

block, covering it with ribbed watch glass or a cap with a central vent, and heating it at 95 ± 5 °C 

for 60 min. The extract is to be brought to a final volume of 50 ml by dilution with reagent grade 

DDW. Given the simpler matrix and reduced sample handling of the hot block digestion method, 

one could reasonably expect to achieve more consistent results (i.e., better precision). There is a 

possibility that deviations from procedures could produce insoluble lead chloride. 

15 
Question 2: What are the panel’s views on ICP-MS as the analysis method for Pb-TSP? 

As stated in the white paper, Pb can be analyzed by ICP-MS, just as it can be analyzed by 

atomic absorption spectrometry (AAS) with a graphite furnace and ICP-atomic emission 

spectroscopy (ICP-AES) once it is in solution. It can be accurately quantified to several orders of 

magnitude below the necessary working range. The ICP-MS should support a method detection 

limit (MDL) of 0.0075 μg/m3. The instrument will be well within its capabilities, resulting in 

accurate and precise results. 

The analysis method for Pb should be performance-based. As long as the MDL, 

precision (±15% at 90% confidence interval), and accuracy (±5%) are within the EPA’s specified 

levels, other analytical methods (e.g., AAS with graphite furnace, ICP-AES, X-ray fluorescence 

[XRF], or proton-induced X-ray emission [PIXE]) should be available as options (e.g., Harper et 

al., 2004; Margui et al., 2005). Unless the state or local agency is already set up for ICP-MS, it 

will be costly to initially identify, procure, and set-up for acid digestion (~$5,000 – 10,000; e.g., 

hot block, flow hood) and ICP-MS (~$200,000). An advantage of ICP-MS is the ability to 

quantify different isotopic abundances for Pb, which may be related to their sources (Moreira et 

al., 2005; Oehme and Lund, 1979; Huggins, 2002; Herner et al., 2006). 

Question 3: What are the panel’s views on the approach described for evaluating and testing the 

method prior to proposal as a new FRM for Pb-TSP? 

The white paper states the proposed approach for determining method performance (i.e., 

analysis of standard reference materials [SRMs], verification of filters spiked with a known 

concentration of NIST traceable Pb salts solution, examination of interference and filter matrix 

effects, determination of MDL, and intra-laboratory method performance [e.g., assess bias within 

±10% and precision within ±15%, evaluation of glass and quartz-fiber filter matrices, analysis of 

spiked filter strips, SRMs, and real-world samples, tests for small variations in extraction 

temperature and time, and evaluation of extract storage stability]). 

Additional tests need to be planned and conducted to ensure 100% extraction efficiency. 

Extraction of spiked-samples with NIST traceable Pb salt or SRMs does not necessarily verify 

the extent of a complex matrix of ambient or source samples. 

Question 4: Inter-laboratory testing of the method will be done to assess between-laboratory 

variability (CV) at the 95% confidence interval. What are the panel’s views on a reasonable 

level of inter-laboratory variability? 

Inter-laboratory testing as listed in the white paper (e.g., method performance assessment 

of the four participating laboratories, analysis of spiked filter samples and actual filter samples) 

is adequate. It would be worthwhile to examine previously published composition for Pb 

analyses. It would also be helpful to specify the concentration range representing the measured 

and calibrated concentration range. The total number of samples to be performed for each type of 

16 
analysis should be more than 10 pairs by each participating laboratory to obtain a statistically 

significant analysis. 

In addition to the calculation of coefficient of variation (CV) at the 95% confidence 

interval, equivalence and comparability should be established for the inter-laboratory comparison 

as defined in Mathai et al. (1990). The U.S. EPA criteria for equivalence between Federal 

Equivalent Methods (FEM) and FRM for PM2.5 mass concentration, such as: 1) linear regression 

slope of 1 ± 0.05; 2) linear regression intercept of 0 ± 1 μg/m3; and 3) linear regression 

correlation coefficient (r) of >0.97 can be modified and adapted for “equivalence.” The 

following criteria can be considered for “comparability” within the stated precision: 1) the slope 

(by either ordinary least squares [OLS] or effective variance [EF] weighting) equals unity within 

three standard errors, or average ratios (y/x) equal unity within one standard deviation; 2) the 

intercept does not significantly differ from zero within three standard errors; and 3) the 

correlation coefficient exceeds 0.9 (Berkson, 1950; Kendall, 1951; Madansky, 1959). This is a 

less demanding definition than equivalence because it considers the reported precisions of the 

two measurements being compared; these may be larger than the requirements for an FEM used 

to determine compliance, but still sufficient to discern concentration differences (Watson and 

Chow, 2002). 

References 

Ashley, K.; Song, R.G.; Esche, C.A.; Schlecht, P.C.; Baron, P.A.; Wise, T.J. (1999). Ultrasonic 

extraction and portable anodic stripping voltammetric measurement of lead in paint, dust wipes, 

soil, and air: An interlaboratory evaluation. J. Environ. Monit., 1(5): 459-464. 

Berkson, J. (1950). Are there two regressions? J. Am. Stat. Assoc., 45: 164-180. 

Harper, M.; Hallmark, T.S.; Andrew, M.E.; Bird, A.J. (2004). A comparison of X-ray 

fluorescence and wet chemical analysis of air filter samples from a scrap lead smelting operation. 

J. Environ. Monit., 6(10): 819-826. 

Herner, J.D.; Green, P.G.; Kleeman, M.J. (2006). Measuring the trace elemental composition of 

size-resolved airborne particles. Environ. Sci. Technol., 40(6): 1925-1933. 

Huggins, F.E. (2002). Overview of analytical methods for inorganic constituents in coal. 

International Journal of Coal Geology, 50(1-4): 169-214. 

Kendall, M.G. (1951). Regressions, structure and functional relationship, Part I. Biometrika, 39: 

96-108. 

Madansky, A. (1959). The fitting of straight lines when both variables are subject to error. J. Am. 

Stat. Assoc., 54: 173-205. 

Margui, E.; Queralt, I.; Carvalho, M.L.; Hidalgo, M. (2005). Comparison of EDXRF and ICPOES after microwave digestion for element determination in plant specimens from an abandoned 

mining area. Anal. Chim. Acta., 549(1-2): 197-204. 

17 
18 

Mathai, C.V.; Watson, J.G.; Rogers, C.F.; Chow, J.C.; Tombach, I.H.; Zwicker, J.O.; Cahill, 

T.A.; Feeney, P.J.; Eldred, R.A.; Pitchford, M.L.; Mueller, P.K. (1990). Intercomparison of 

ambient aerosol samplers used in western visibility and air quality studies. Enivron. Sci. Technol., 

24(7): 1090-1099. 

Moreira, F.R.; Borges, R.M.; Oliveira, R.M. (2005). Comparison of two digestion procedures for 

the determination of lead in lichens by electrothermal atomic absorption spectrometry. 

Spectrochimica Acta Part B-Atomic Spectroscopy, 60(5): 755-758. 

Oehme, W.; Lund, W. (1979). Comparison of digestion procedures for the determination of 

heavy metals (cadmium, copper, lead) in blood by anodic stripping voltammetry. Fresenius Z. 

Anal. Chem., 298: 260-268. 

U.S.EPA (2007). 40 CFR Ch. I; Appendix G to Part 50 - Reference Method for the 

Determination of Lead in Suspended Particulate Matter Collected from Ambient Air. Federal 

Register, 50: 57-61. 

Watson, J.G.; Chow, J.C. (2002). Comparison and evaluation of in-situ and filter carbon 

measurements at the Fresno Supersite. J. Geophys. Res., 107(D21): ICC 3-1-ICC 3-15. doi: 

10.1029/2001JD000573. 
Comments from Mr. Bart Croes 

Staff should be commended for taking a systematic approach towards implementation of 

the revised National Ambient Air Quality Standard (NAAQS) for lead (Pb) in total suspended 

particulates (TSP). I appreciate the opportunity to comment during several stages of the process, 

and agree with the general approach taken by U.S. EPA toward extraction and analysis as 

described in the white paper. My comments reflect input from California Air Resources Board 

(ARB) staff responsible for implementing U.S. EPA monitoring requirements and using the data 

in source apportionment and health studies. 

Charge Questions: 

1. What are the panel’s views on the two extraction method options of heated ultrasonic and 

graphitic hot block with nitric/hydrochloric acid for the extraction of Pb from TSP? 

Both methods are acceptable for extraction of Pb from TSP for NAAQS compliance 

purposes. Since SLT agencies are already extracting Pb as part of source apportionment and air 

toxics monitoring networks, and want to conserve resources, this flexibility is desirable. Pb is 

easy to extract, but it would be desirable to have performance standards for extraction efficiency 

in order to demonstrate equivalency for data from other existing networks. 

2. What are the panel’s views on ICP-MS as the analysis method for Pb-TSP? 

ICP-MS is preferred as the FRM, but other analytical methods besides should be allowed. 

The ARB air toxics network (Xontech 924, low volume sampler TSP, Teflon filter) uses ICP-MS 

for toxic metals, including Pb, because of high accuracy and precision across many species (in a 

single scan) over the entire ambient concentration range. 

The Flame Atomic Absorption Spectroscopy (FAAS) method is used for the existing high 

volume sampler TSP-Pb network by many SLT agencies, and also has good precision and 

accuracy. The FAAS method should be retained as an FEM. ARB’s high volume sampler TSPPb network uses Graphite Furnace Atomic Absorption Spectroscopy (GFAAS) and has a 

1.0 ng/m3

 (0.0010 μg/m3) limit of detection (LOD), far below the new NAAQS of 0.15 

μg/m3

. A cursory look at the last few months of data from two FRM sites (Calexico and 

Tijuana) showed all results to be well above this LOD. The GFAAS method should be retained 

as an FEM. 

3. What are the panel’s views on the approach described for evaluating and testing the method 

prior to proposal as a new FRM for Pb-TSP? 

With the inclusion of the AAS methods discussed above, the approach described for 

evaluating and testing the proposed analytical method for a Pb-TSP FRM appears adequate, 

especially the range of spiked and ambient samples and number of proposed facilities (four) for 

the inter-laboratory comparison. The criteria that each laboratory will achieve bias (accuracy) 

≤10% and precision ≤15% for the spiked filter strips seems loose and could be tightened. 

19 
Typically, the ARB laboratory sees ≤5% bias and ≤5% precision for metals analyses, but perhaps 

≤10% for both is a more realistic expectation. 

4. Inter-laboratory testing of the method will be done to assess between-laboratory variability 

(CV) at the 95% confidence interval. What are the panel’s views on a reasonable level of interlaboratory variability? 

An inter-laboratory bias (accuracy) ≤10% and precision ≤15% for the group of 

measurements that make up a 3-month average is a reasonable expectation. The inter-laboratory 

comparison should be weighted toward the ambient samples and spiked samples that are near the 

level of the NAAQS. 

20 
21 

Comments from Dr. Kenneth Demerjian 

Charge question 1. What are the panel’s views on the two extraction method options of heated 

ultrasonic and graphitic hot block with nitric/hydrochloric acid for the extraction of Pb from 

TSP? 

The ideal approach would be to develop performance based standards (quantification of 

extraction efficiency) from which to quantify acceptable extraction procedures. The design of an 

intercomparison study which would consider a wide-range of real-world samples (i.e. spanning 

filter loading and particle composition) to evaluate these techniques will result in substantial 

additional work for EPA. Although many versions of the traditional extraction approach using 

heated ultrasonic water bath with nitric/hydrochloric acids have been used successfully, they do 

not represent the current state-of-art (e.g. microwave digestion). If the agency or states view the 

Pb measurement approach as an opportunity to consider the measurement of other PM metals the 

newer digestion technologies may be of even greater interest. 

Charge question 2. What are the panel’s views on ICP-MS as the analysis method for Pb-TSP? 

The ICP-MS is the state-of-art measurement method of choice. 

Charge question 3. What are the panel’s views on the approach described for evaluating and 

testing the method prior to proposal as a new FRM for Pb-TSP? 

The subject white paper provides an acceptable description and adequate guidance 

regarding the development of a new FRM for Pb-TSP and QA/QC requirements. 

Charge question 4. Inter-laboratory testing of the method will be done to assess between 

laboratory variability (CV) at the 95% confidence interval. What are the panel’s views on a 

reasonable level of inter-laboratory variability? 

The proposed inter-laboratory testing procedures as outlined are adequate to judge the 

performance and acceptability of individual laboratories. Differences in laboratory performance 

may likely reside from sampling handling and preparation (i.e. extraction). An assessment of the 

typical variability in extraction efficiencies may be the determining factor in what should be 

viewed as to reasonable level of inter-laboratory variability. 
Comments from Dr. Delbert J. Eatough 

Individual response to Charge Questions for the Clean Air Scientific Advisory 

Committee’s (CASAC) Ambient Air Monitoring & Methods Subcommittee Peer Review on the 

Approach for the Development of a New Federal Reference Method (FRM) for Lead (Pb) in 

Total Suspended Particulates (TSP). 

Prepared in connection with the AAMMS committee consensus response to EPA in 

connection with the September 15, 2010 AAMMS call. 

1. What are the panel’s views on the two extraction method options of heated ultrasonic and 

graphitic hot block with nitric/hydrochloric acid for the extraction of Pb from TSP? 

EPA is proposing to replace the current extraction method described in Appendix G of 40 

CFR Part 50 with one of the two methods listed above. The essence of the three methods, as I see 

it, are compared in the following Table. 

Method Current Method Ultrasonic Bath Hot Block Reflux 

Fraction Analyzed 3⁄4” x 8” strip 3⁄4” x 8” strip 3⁄4” x 8” strip 

Solution 15 mL, 3 M HNO3 15 mL, 1 M HNO3, 

2 M HCl 

20 mL, 1:19 v/v 

HNO3

Extraction 30 min, boiling 60 min, 80 oC 60 min, 95 oC 

From a chemical extraction point of view, the three methods should be nearly equivalent 

for the extraction of Pb from particles collected on either a glass or quartz fiber filter. As pointed 

out in the EPA material provided for the consultation, the HCl added to the Ultrasonic Bath 

technique will assist in the extraction of more refractory metals from the sample, but is not 

needed for the recovery of Pb. From, a personal point of view, I prefer the Ultrasonic Bath 

technique because it minimizes the temperature to which the concentrated nitric acid solution is 

heated. This method does, however add and additional step to remove the fibers produced. As 

pointed out by others, all of the techniques are a little dated. Using a more current technique, 

such as microwave digestion would be preferable. However, the more important question is the 

blank, Pb recovery, and precision of each technique. These points cannot be established from the 

material provided. The two newer techniques proposed by EPA for evaluation are covered in two 

reports referenced in the white paper, e.g. EQL-0510-191,Determination of Lead in TSP by 

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) with Heated Ultrasonic Nitric and 

Hydrochloric Acid Filter Extraction and EQL-0710-192, Heated Nitric Acid Hot Block 

Digestion and ICP-MS Analysis for Lead (Pb) on TSP High-Volume Filters. The first is a report 

from RTI to EPA on the indicated method and the second a method description from U.S. EPA 

Region 9. Neither are complete scientific reports, giving details on the data behind the various 

statements in the documents. The above listed important points of method blank, Pb recovery 

and precision of the techniques cannot be established from these reports. 

Likewise, there are no studies from any given laboratory which allow comparisons of the 

three techniques. EPA is planning a detailed laboratory study as part of the protocol moving 

22 
forward. This will be a valuable step and should do much to better define important elements 

which should be part of the EPA inter-laboratory evaluation and testing program to follow. 

Finally, I would like to suggest that all three methods, plus microwave extraction, and not 

just the two outlined in the white paper should be evaluated on an equal footing. This will 

provide a tie to previous analyses and give an indication as to whether a change from the older 

analytical scheme is needed with respect to the extraction method. 

2. What are the panel’s views on ICP-MS as the analysis method for Pb-TSP? 

The analytical techniques used for the determination of Pb in the various extract solutions 

to be analyzed, as outlined in charge question 1, is required by EPA to have a MDL for Pb of 5% 

of the NAAQS (0.15 μg/m ), or 0.008 μg/m . As recently summarized by C 3 3 avender (EPA, 

OAQPS) in a presentation at the March 2, 2009 National Air Quality Conference in Addison, 

TX, expected MDLs for Pb in TSP and PM10 methods are: 

Estimated MDL: (μg/m3) Sample Analysis Methods

0.002 to 0.00005 a,c Graphite Furnace Atomic Absorption (GFAA) 

0.0007 b Energy-dispersive X-Ray Fluorescence (EDXRF) 

0.00006 c Inductively Coupled Plasma Mass Spectrometry (ICP-MS) 

0.0003 c Inductively Coupled Plasma Atomic Emission spectrometry 

(ICP-AES/OES) 

a Estimated MDL retrieved from AQS 

b 40 CRF Part 50, Appendix Q 

c Estimated MDLs reported in the Inorganic (IC) Compendium of Methods for the 

Determination of Inorganic Compounds in ambient Air, EPA/625/R-96/01a, July 1999 

Each of the methods listed above are capable of given data within the required MDL. 

While ICPMS has the anticipated lowest MDL in the Table, this extra level of lower detection is 

not needed for the purposes of the NAAQS for Pb as currently outlined. While evaluating the 

ICP-MS method as an alternate method for data analysis would be warranted, I see no reason to 

dump the long standing GFAA method for which we have decades of experience. Moving ahead 

with both methods in the evaluation proposed by EPA would seem warranted. The comparison 

of the two methods will enhance our understanding of both precision and accuracy in the 

determination of Pb under the current standard. Since both methods will use the various extract 

solutions outlined in charge question 1, there is no practical impediment to this approach. 

I would like to make a few final points in regards to the above Table. All of the 

techniques, except for EDXRF analysis are ideally suited for analysis of solutions, such as those 

produced by the procedures highlighted under charge question 1. However, the procedures 

required to produce those solutions are laborious, expensive and prone to sample contamination 

introduction. The solution extraction approach is required under the current FRM technique for 

Pb in TSP. But making an effort to move any from this requirement would be highly desirable. 

23 
EPA has put in place the possibilities for both low volume TSP samplers or the acceptance of a 

PM10 value for Pb measurements in the future in the 40 CFR 50 document. These were both 

directions the AAMMS urged EPA to move in the past and I encourage EPA to actively 

incorporate evaluation of these methods into some phases of the development of FRMs for Pb. If 

such a path. is not taken, then comparison data which would allow the incorporation of either a 

low volume TSP sampler or a PM10 metric in the future will not be obtained and moving one of 

these directions will not be possible. Either technique would allow the use of EDXRF (or 

equivalent methods) for the direct analysis of collected samples without an extraction step. This 

would be highly desirable. 

3. What are the panel’s views on the approach described for evaluating and testing the method 

prior to proposal as a new FRM for Pb-TSP? 

As outlined in the charge questions and in the white paper, the approach which EPA will 

take to validate any new methods for analysis of TSP PB is based on the guidance documents 

and references provided with the charge questions. Particular weight is given to information 

contained in Validation and Peer Review of U.S. Environmental Protection Agency Chemical 

Methods of Analysis, prepared for The EPA Forum on Environmental Measurements (FEM); 

FEM Document Number 2005-01, October 14, 2005. The approach to be used includes the 

analysis of Standard Reference Materials (SRMs) and NIST-traceable Pb salt solutions; 

assessment of method detection limits (MDLs), bias, precision; and inter-laboratory testing to 

assess between laboratory variability. The approach is reasonable, well thought out and based on 

solid guidance to EPA. I urge EPA to keep in focus the point that the lowest MDL is not the 

prime factor which should be considered in making a decision. As long as any analytical 

technique has a MDL within the requirements of the standard, it should be evaluated on an equal 

footing with the methods with the lowest MDL. There are three important modifications I would 

suggest to the approach outlined in the white paper: 

(1). Include in the single laboratory evaluation of the four extraction methods outlined 

in 1. above to better inform the process and set the protocols as EPA moves into 

multilaboratory evaluations. 

(2). Include a minimum of both ICP-MS and GFAA in both the single laboratory 

study and multi-laboratory evaluations so that there is a solid basis for either 

retaining the GFAA method in the FRM (along with ACP-MS if adopted) or 

switching to only the ICP-MS method. I urge this evaluation because of the 

legacy in both data and laboratory experience with the current analytical method. 

(3). Include comparison measurements with both a low flow TSP sampler and a PM10 

sampler to develop a data set which would allow EPA to consider moving away 

from the high volume TSP sampling procedure in the future. I particularly urge 

EPA to include the PM10 measurements and direct analysis of the collected filter 

material to allow the Pb program to become more consistent with sampling for the 

PM standard in the future. 

24 
25 

4. Inter-laboratory testing of the method will be done to assess between-laboratory variability 

(CV) at the 95% confidence interval. What are the panel’s views on a reasonable level of interlaboratory variability? 

I concur with the points in the consensus report. 
Comments from Mr. Dirk Felton 

General Comment 

The FRM for TSP Pb suffers from relatively high measurement uncertainties at the 

higher concentrations near the NAAQS. This error is apparent from the field precision data 

which includes variability due to sampler collection efficiency. The high volume TSP samplers 

specified for use in the NAAQS program have variable collection efficiency due to wind 

direction and wind speed. These sampler related collection errors are proportionally larger as the 

concentration of Pb in the air increases. The graph below shows that when the ambient Pb 

concentration nears the new NAAQS, the difference in concentration between the primary and 

duplicate samplers increases. This increase in error is not related to extraction efficiencies which 

are summarized in the next plot. Duplicate extractions are performed by extracting and 

analyzing a second strip from the same filter. The 2009 Pb QA data provided by the NYSDEC 

indicates that the current extraction and analysis methods are adequate but the field collection of 

Pb samples needs improvement. 

26 
ICPMS is used by most monitoring agencies in the NATTS program for the analysis of 

low-volume PM-10 filters for toxics metals including Pb. The data for this program is used for 

trends determinations and risk assessments so data accuracy is important throughout the 

concentration range. The accuracy and sensitivity of the analysis must be much better than for 

the Pb high volume analysis because of the smaller sampling volume for these samplers. The 

results from the collocated non-source oriented NATTS site in New York demonstrate that the 

low volume field samplers with ICPMS analysis produce very high quality data. 

27 
28 

Response to Charge Questions 

1. What are the panel’s views on the two extraction method options of heated ultrasonic and 

graphitic hot block with nitric/hydrochloric acid for the extraction of Pb from TSP? 

Either extraction method is acceptable for NAAQS Pb monitoring. Monitoring Agencies 

are likely to prefer one method over another because it is either cost effective or because it is 

better suited for the analyses of other elements. 

Since Pb is relatively easy to extract, it would be preferable to have a range of acceptable 

extraction parameters such as acid types and concentrations, temperatures, heating methods and 

filtration included in the FRM. Performance standards for extraction efficiency could be 

included to ensure that the method selected by specific laboratories is adequate for compliance 

data. This approach would not only make the samples collected for Pb NAAQS monitoring 

useful for other programs but will also make the samples collected for other programs such as air 

toxics eligible for use in comparison to the Pb NAAQS. 

2. What are the panel’s views on ICP-MS as the analysis method for Pb-TSP? 

The method is acceptable but is more accurate than is necessary for high volume TSP 

filter analysis. The advantage of making this method a FRM is that it is also suitable for use with 

low volume PM-10 filters. The FAAS method is adequate for high volume sample analysis and 

is performed in-house by many State and Local monitoring agencies. The FAAS method should 

be retained as an FEM but limited to use for high volume samples. 

3. What are the panel’s views on the approach described for evaluating and testing the method 

prior to proposal as a new FRM for Pb-TSP? 

The approach looks adequate though some of the evaluation criteria are not very tight. 

Recoveries, inter-method precisions and bias at high concentrations should be better than the 

criteria set forth in the white paper. The criteria should be tightest at the level of the NAAQS. 

The sampled filters should also be selected to look for real world interferences. The 

white paper mentions that filters will be selected to cover a range of Pb but they should also 

cover a range of other factors such as heavy crustal or EC loadings that may potentially interfere 

with the analysis results. 

4. Inter-laboratory testing of the method will be done to assess between-laboratory variability 

(CV) at the 95% confidence interval. What are the panel’s views on a reasonable level of interlaboratory variability? 

The comparisons between labs should include criteria that indicate performance at low 

concentrations, high concentrations and of course at the level of the NAAQS. The evaluation 

should also emphasize the performance for real world samples. 
Comments from Dr. Philip Hopke 

1. What are the panel’s views on the two extraction method options of heated ultrasonic and 

graphitic hot block with nitric/hydrochloric acid for the extraction of Pb from TSP?

The methods proposed appear to be adequate for extracting lead from TSP samples, but 

they have failed to evaluate modern extraction techniques. There is no discussion of microwave 

digestion where you can automate multiple samples. There are systems that can run up to 40 

samples at a time with monitoring of the temperature of each extraction cell to ensure uniform 

extraction. Thus, the Agency has missed an opportunity to permit efficient, uniform extraction 

that would make the analyses faster, more uniform and simpler to run in large numbers. 

2. What are the panel’s views on ICP-MS as the analysis method for Pb-TSP? 

ICP-MS is an appropriate method. 

29 
Comments from Dr. Peter McMurry 

1. What are the panel’s views on the two extraction method options of heated ultrasonic and 

graphitic hot block with nitric/hydrochloric acid for the extraction of Pb from TSP?

I am not an expert on methods used for extracting Lead (Pb), so I will not to comment on 

them. 

2. What are the panel’s views on ICP-MS as the analysis method for Pb-TSP? 

Again, I have no particular expertise on analytical methods used to determine Lead (Pb) 

concentrations, so I will not comment on the choice of ICP-MS as the analysis method for the 

FRM. My only concern about this is that if state or local agencies use another method that 

produces equivalent results, then perhaps it should also be allowed. 

3. What are the panel’s views on the approach described for evaluating and testing the method 

prior to proposal as a new FRM for Pb-TSP? 

My primary concern is that the standard involves the analysis of samples collected with a 

TSP sampler. There must be a reason that TSP samplers are used rather than, for example, PM10. 

Are TSP samplers also used for other types of sampling? It would seem that mandating TSP as 

well as PM10 sampling would impose unnecessary burdens on state and local agencies. Also, 

TSP samples are less well characterized than PM10 samples. 

Other AAMM members have had more experience than I at method evaluation. I defer to 

their judgement on this topic. 

4. Inter-laboratory testing of the method will be done to assess between-laboratory variability 

(CV) at the 95% confidence interval. What are the panel’s views on a reasonable level of interlaboratory variability? 

It would appear that the interlaboratory testing plan is based on well-established 

paradigms. 

What procedures will be employed to ensure that a given laboratory continues to analyze 

samples accurately over time, after the initial intercomparison is complete? 

30 
Comments from Dr. Jay Turner 

It is appropriate that the Agency revise the FRM for Pb-TSP to provide for suitable 

sample analyses to determine compliance with the Pb NAAQS revisions promulgated in 

November 2008. Advice has been solicited concerning the extraction and analytical methods, 

method validation and testing, and target for inter-laboratory variability. 

I commend the EPA for the thoughtful approach that is being taken to the revisions, 

including the proposed methods evaluation study. 

Charge Questions and Responses 

1. What are the panel’s views on the two extraction method options of heated ultrasonic and 

graphitic hot block with nitric/hydrochloric acid for the extraction of Pb from TSP? 

The two methods (EQL-0510-191 and EQL-710-192) are reasonable candidate methods. 

They are consistent with current laboratory equipment and practices. Our group’s recent 

experience with graphite hot block sample digestions for air toxics PM10 metals (including but 

not limited to Pb) has been very positive. 

I am comfortable with more than one extraction method being included in the FRM. My 

key concern is that clear equivalency criteria be developed so that additional, commonly-used 

extraction protocols can designated as FEM methods. It would be beneficial if EPA included 

certain additional extraction methods in the proposed evaluation study and made the FEM 

designations, rather than placing this burden on state/local agencies. For example, Pb is a target 

analyte for the National Air Toxics Trends Station (NATTS) network PM10 metals 

measurements. Given that several state/local agencies are already performing these analyses, it 

might be advantageous if the same extraction method could be used for the Pb-TSP analysis. 

On a technical note, the extraction description in EQL-710-192 concludes with the step 

“Shake the extract vigorously for 5 seconds (with the filter strip in the extraction vessel) and let 

settle for at least an hour. The sample is now ready for analysis.” What are the provisions for 

storing the sample(s) for some length of time between extraction and analysis? Also, does the 

one hour of settling time guarantee that no filtration of the extract is required? A filtration step is 

included in EPA Compendium Method IO-3.1 (Selection, Preparation, and Extraction of Filter 

Material), the metals extraction SOP posted under the air toxics section of the EPA AMTIC web 

site (http://www.epa.gov/ttnamti1/files/ambient/airtox/metalsop.pdf), and the Technical 

Assistance Document for the National Air Toxics Trends Station Program (Revision 2, April 

2009; http://www.epa.gov/ttn/amtic/files/ambient/ inorganic/mthd-3-5.pdf). 

What are the plans for the initial demonstration of performance for each analytical 

laboratory? While the candidate methods will be evaluated using the Text Matrix appended to 

the White Paper, would there be advantages to having each analytical laboratory perform tests 

31 
32 

with SRM or some other standardized samples as part of an initial demonstration of 

performance? This is not addressed in the candidate SOPs. 

 

2. What are the panel’s views on ICP-MS as the analysis method for Pb-TSP? 

ICP-MS is appropriate as the reference method. It has suitable sensitivity and minimal 

issues with interferences. In addition to contract laboratories. many state/local agencies are 

already performing ICP-MS analysis for air toxics PM10 metals (see e.g. Table 8 in National Air 

Toxics Trends Stations Quality assurance Annual Report, Calendar Year 2007; 

http://www.epa.gov/ttnamti1/files/ambient/airtox/NATTS2007QAAnnualReport.pdf). Again, 

there might be advantages to harmonization with the NATTS method which is EPA 

Compendium Method IO-3.5 (Determination of Metals in Ambient Particulate Matter Using 

Inductively Couple Plasma/Mass Spectrometry). The EPA should consider including GFAAS in 

the proposed evaluation study, possibly leading to designation as an FEM directly by the Agency. 

Also, FAAS should be included in the evaluation study to provide connection to historical 

analysis methods. 

I encourage the designation of a single analytical method as the FRM, specifically a 

method that has sufficiently high sensitivity to be suitable should the Pb NAAQS concentration 

threshold be revised downward at a later time. In this case, any additional qualifying methods 

for the current standard could be designated as FEM. 

3. What are the panel’s views on the approach described for evaluating and testing the method 

prior to proposal as a new FRM for Pb-TSP? 

The approach is sound although the test criteria ideally would be framed within the 

context of a DQO, but there is no evidence that this has been done. Tests and criteria have been 

defined in the Test Matrix appended to the White Paper. I have some concerns about the broad 

range for the SRM recoveries (80-120%). While this recovery range is a commonly used 

criterion, should it be tighter for NAAQS compliance measurements? Also, should recovery 

tests be performed at even higher nominal mass loadings? The NAAQS is based on a threemonth rolling average. For 1-in-6 day sampling this is nominally 15 samples and thus a few very 

high concentration samples could lead to a violation and it would be important to have accurate 

measurements at high concentrations since the NAAQS is an arithmetic average. 

4. Inter-laboratory testing of the method will be done to assess between-laboratory variability 

(CV) at the 95% confidence interval. What are the panel’s views on a reasonable level of interlaboratory variability? 

The target performance for inter-laboratory variability should take into consideration the 

overall measurement quality objectives and the performance achieved by the method(s) from the 

intra-laboratory method performance evaluation. 
Comments from Dr. Warren White 

As usual, I am impressed by the care and consideration the Agency gives to defining its 

compliance measurements. I would also like to commend the authors of this white paper for 

their inclusion of hyper-links to relevant Agency documents (on pages 1 and 2), which can 

sometimes be hard for outsiders to locate. 

I bring no specific personal expertise to this review, having no direct experience with 

either high-volume (TSP) sampling or ICP-MS analysis. My comments accordingly focus on the 

statistical aspects of the inter-laboratory testing, responding to charge question #4. 

The experimental design for inter-laboratory testing is said to follow, generally, that of 

Long et al. (1979). For tests on sampled filters, it anticipates selecting 28 = 7x2x2 archived 

high-volume filters. This will provide 7 ambient levels on each of 2 filter media (glass and 

quartz), for extraction by 2 different procedures (heated ultrasonic and heated block). Each highvolume filter will be sectioned into eight strips; four pairs of adjacent strips will be distributed to 

four different laboratories. Each laboratory will analyze each extract in triplicate and report the 

individual results. The resulting data set will support the analysis of variance techniques with 

which Long et al. resolved observed variations into components attributable to within-laboratory 

and between-laboratory standard deviations. 

In the Long et al. inter-laboratory evaluation, the role of the paired strips was to provide 

matched tests of the alternative extraction procedures: “Each laboratory was requested to extract 

one strip of each pair with the boiling HNO3 procedure and the other with the ultrasonic HNO3 

procedure.” This matching provided more statistical power for testing the equivalence of the two 

extraction procedures. The present white paper instead envisions that “Each laboratory will 

receive 7 pairs for the heated block method and 7 pairs for the heated ultrasonic method.” This 

means that the two extractions will be tested on unmatched samples, making their equivalence 

more difficult to assess. The experimental design could be improved by splitting each pair 

between the two extraction procedures, as was done by Long et al. This return to the earlier 

design would also reduce the required number of archived filters (and lab analyses) by one-half, 

to 14. 

If more than four laboratories or two extraction methods might be compared, this would 

require some reconfiguration of the present design. It is also worth noting that the interlaboratory discussion (pp. 27-28) in the EPA methods development and validation guidance 

(USEPA, 1992), cited by the white paper, explicitly calls for decoupling the tests of the 

extraction and determinative procedures: 

When validating a sample preparation method, the participating laboratories should only 

perform the sample preparation procedure. The collected samples should then be sent to 

one laboratory for analysis. The analysis should be done by a single operator on a single 

instrument in a single batch to minimize analytical variability inherent to the 

determinative method. Conversely, if a determinative method is to be validated, the 

developer should have a single operator perform all of the sample preparation 

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operations in order to minimize operator and laboratory variability inherent to the 

sample preparative procedures. The sample extracts should then be split and sent to the 

laboratories participating in the validation study for the analytical determination. 

On the charge question of “a reasonable level of inter-laboratory variability”, we can note 

that Long et al. judged that two observations by different laboratories using the previous FRM 

would not differ by more than 28% of the concentration level more than 5% of the time due to 

chance alone. Alternatively, if 10% bias and 15% precision are tolerated for each lab, then 

differences of 50% = 2.77 x (10%2

+15%2)

1/2 could be expected 5% of the time. [The factor 2.77 

is the two-sided 5% critical value (1.96) for the normal distribution, multiplied by the square root 

of two to account for the independent uncertainties in two observations.] For comparisons 

between n-sample averages, differences of 2.77 x (10%2

+15%2/n)1/2 could be expected 5% of the 

time. Averaging 16 (three months of one-day-in-six sampling) observations, for example, would 

thus reduce the 5% confidence level difference from 50% to 30%. 

Whether these are “reasonable” levels of variability requires a consideration of data 

quality objectives (USEPA, 2006). Given the epistemic uncertainties in our exposure and risk 

assessments for lead, an acceptable level of uncertainty for the indicator cannot be derived from 

scientific principles alone. 

USEPA, 1992. Development and Validation of SW-846 Methods Phase 2: Formal Validation. In 

Guidance for the Methods Development and Methods Validation for the RCRA Program, 

Washington, DC. 

USEPA, 2006. Guidance on Systematic Planning Using the Data Quality Objectives Process. 

EPA/240/B-06/001, Washington, DC. Available at: http://www.epa.gov/quality/qs-docs/g4-

final.pdf
Comments from Dr. Yousheng Zheng 

Charge Question 1: What are the panel’s views on the two extraction method options of heated 

ultrasonic and graphitic hot block with nitric/hydrochloric acid for the extraction of Pb from 

TSP? 

EPA has presented two options for lead extraction from TSP filters – Option 1: heated 

ultrasonic nitric and hydrochloric acid filter extraction, and Option 2: heated nitric acid hot block 

digestion. I don’t have experience with these two specific extraction procedures. However, based 

on my past experience with acid digestion of TSP samples, the mixture of nitric acid and 

hydrochloric acid provides more aggressive and thorough extraction of metals than nitric acid 

alone. More aggressive extraction may or may not be important for lead. It certainly makes 

difference for extracting some other metals. With ICP-MS, multiple metal analyses will be easier 

than the current FRM using FAAS. Multiple metal analyses will provide more useful information 

for source identification and apportionment. With the ease and value of having multiple metals 

analyses, it is anticipated that more agencies would analyze multiple metals beyond lead. 

Therefore, a procedure that has stronger digestion and extraction power for not only lead, but 

also other metals is beneficial. 

In addition to hydrochloric acid, Option 1 uses a slightly higher nitric acid concentration 

than Option 2 (64.4 mL of concentrated nitric acid in 1000 mL vs. 50 mL in 1000 mL). Option 1 

also uses ultrasonic waves to provide agitation and to aid extraction. 

Overall, Option 1seems to be a stronger method than Option 2. Unless Option 1 is more 

susceptible to interference due to presence of hydrochloric acid or chlorides, I would favor 

Option 1. As part of EPA’s further evaluation of the two candidate methods before final selection 

of the FRM, I would suggest that EPA address vulnerability between the two methods in terms 

of potential interference in the two methods, i.e., does the presence of hydrochloric acid make 

the subsequent ICP-MS analysis more susceptible to interference in the context of a typical 

ambient TSP samples as the matrix? As stated in Section 7.2 of SW-846 Method 6020A, “many 

more molecular-ion interferences are observed when hydrochloric and sulfuric acids are used”. 

This question may have been investigated and answered, but not included in the materials 

provided for this subcommittee review. 

Charge Question 2: What are the panel’s views on ICP-MS as the analysis method for Pb-TSP? 

EPA has cited the advantages of using ICP-MS over the current FRM analytic method 

(FAAS). I agree that ICP-MS should be a significantly better method than FAAS. My only 

comments are: 

1. Potential interferences (including isobaric elemental interferences, physical and 

chemical interferences, and interferences that may be caused by introduction of 

hydrochloric acid as discussed above;) should be addressed as part of EPA’s 

evaluation. 

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2. If possible, EPA should consider some secondary objectives to leverage and 

maximize the benefits of conducting the evaluation. These secondary evaluations may 

include: 

a. Analyzing other elements in addition to Pb. If the results are favorable, they 

can be used to support monitoring agencies’ effort to analyze multiple 

elements at a small incremental cost and acquire valuable data for other 

programs such as air toxics studies, source apportionment, etc. 

b. Analyzing samples using the current FRM (i.e., FAAS) and XRF method in 

parallel to the evaluation of the candidate ICP-MS methods so that 

comparisons can be made. A comparison with FAAS may help understand the 

past monitoring data and bridge the past and future data. A comparison with 

XRF may be useful because a large body of data has been and can be 

generated by XRF. 

3. The candidate FRM methods are designed for analyzing TSP filters collected by high 

volume samplers. With a large number of PM10 samplers in operations, it would be 

desirable to evaluate suitability of applying the candidate ICP-MS methods to the 

PM10 filters collected by more widely used PM10 samplers. If the new ICP-MS 

based FRM is also suitable for analyzing the PM10 filters collected by common 

PM10 samplers, it will make it easier for monitoring agencies to analyze these filters 

for Pb and other metals, not necessarily for lead NAAQS attainment determination 

but for other air programs. 

Charge Question 3: What are the panel’s views on the approach described for evaluating and 

testing the method prior to proposal as a new FRM for Pb-TSP? 

The proposed approach seems to be comprehensive. I don’t have specific comments at 

this time. 

Charge Question 4: Inter-laboratory testing of the method will be done to assess betweenlaboratory variability (CV) at the 95% confidence interval. What are the panel’s views on a 

reasonable level of inter-laboratory variability? 

The proposed inter-laboratory variability level seems to be reasonable. I don’t have 

specific comments at this time.