EPA IO 3.3

EPA/625/R-96/010a Compendium of Methods for the Determination of Inorganic Compounds in Ambient Air Compendium Method IO-3.3 DETERMINATION OF METALS IN AMBIENT PARTICULATE MATTER USING X-RAY FLUORESCENCE (XRF) SPECTROSCOPY Center for Environmental Research Information Office of Research and Development U.S. Environmental Protection Agency Cincinnati, OH 45268 June 1999 ii Method IO-3.3 Acknowledgments This Method is a part of Compendium of Methods for the Determination of Inorganic Compounds in Ambient Air (EPA/625/R-96/010a), which was prepared under Contract No. 68-C3-0315, WA No. 2-10, by Midwest Research Institute (MRI), as a subcontractor to Eastern Research Group, Inc. (ERG), and under the sponsorship of the U.S. Environmental Protection Agency (EPA). Justice A. Manning, John O. Burckle, Scott Hedges, Center for Environmental Research Information (CERI), and Frank F. McElroy, National Exposure Research Laboratory (NERL), all in the EPA Office of Research and Development, were responsible for overseeing the preparation of this method. Other support was provided by the following members of the Compendia Workgroup: • James L. Cheney, U.S. Army Corps of Engineers, Omaha, NE • Michael F. Davis, U.S. EPA, Region 7, KC, KS • Joseph B. Elkins Jr., U.S. EPA, OAQPS, RTP, NC • Robert G. Lewis, U.S. EPA, NERL, RTP, NC • Justice A. Manning, U.S. EPA, ORD, Cincinnati, OH • William A. McClenny, U.S. EPA, NERL, RTP, NC • Frank F. McElroy, U.S. EPA, NERL, RTP, NC • William T. "Jerry" Winberry, Jr., EnviroTech Solutions, Cary, NC This Method is the result of the efforts of many individuals. Gratitude goes to each person involved in the preparation and review of this methodology. Author(s) • Bob Kellog, ManTech, RTP, NC • William T. "Jerry" Winberry, Jr., EnviroTech Solutions, Cary, NC Peer Reviewers • David Brant, National Research Center for Coal and Energy, Morgantown, WV • John Glass, SC Department of Health and Environmental Control, Columbia, SC • Roy Bennet, U.S. EPA, RTP, NC • Charles Lewis, EPA, RTP, NC • Ray Lovett, West Virginia University, Morgantown, WV • Lauren Drees, U.S. EPA, NRMRL, Cincinnati, OH DISCLAIMER This Compendium has been subjected to the Agency's peer and administrative review, and it has been approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. iii Method IO-3.3 Determination of Metals in Ambient Particulate Matter Using X-Ray Fluorescence (XRF) Spectroscopy TABLE OF CONTENTS Page 1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-1 2. Applicable Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-2 2.1 ASTM Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-2 2.2 U.S. Government Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-3 2.3 Other Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-3 3. Summary of Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-3 4. Significance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-4 5. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-4 6. Description of Spectrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-5 7. Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-6 8. Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-7 9. Spectral Acquisition and Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-7 10. Data Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-9 11. Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-9 12. Detection Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-10 13. Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-11 14. Precision and Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-12 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3-12 iv [This page intentionally left blank.] June 1999 Compendium of Methods for Inorganic Air Pollutants Page 3.3-1 Chapter IO-3 CHEMICAL SPECIES ANALYSIS OF FILTER-COLLECTED SPM Method IO-3.3 DETERMINATION OF METALS IN AMBIENT PARTICULATE MATTER USING X-RAY FLUORESCENCE (XRF) SPECTROSCOPY 1. Scope 1.1 During a span of more than two decades, the U. S. Environmental Protection Agency (EPA) has developed and applied x-ray fluorescence (XRF) to the analysis of ambient and source aerosols using both energy and wavelength dispersive spectrometers. Inorganic Compendium Method IO-3.3 briefly describes the agency's experience with XRF and informs the reader of its capability in elemental aerosol analysis and attempts to give a brief account of what is involved in its application. The procedures described have been in a continual state of evolution beginning with those in use on a special purpose spectrometer designed by Lawrence Berkeley Laboratory (LBL) and eventually applied to a commercially available instrument manufactured by Kevex. It is for the Kevex spectrometer to which this method applies. 1.2 The area of toxic air pollutants has been the subject of interest and concern for many years. Recently the use of receptor models has resolved the elemental composition of atmospheric aerosol into components related to emission sources. The assessment of human health impacts resulting in major decisions on control actions by Federal, state, and local governments is based on these data. Accurate measures of toxic air pollutants at trace levels is essential to proper assessments. 1.3 Suspended particulate matter (SPM) in air generally is considered to consist of a complex multi-phase system consisting of all airborne solid and low vapor pressure, liquified particles having aerodynamic particle sizes ranging from below 0.01 microns to 100 (0.01 Fm to 100 Fm) microns and larger. Historically, measurement of SPM has concentrated on total suspended particulates (TSP) with no preference to size selection. 1.4 The most commonly used device for sampling TSP in ambient air is the high-volume sampler, which consists essentially of a blower and a filter, and which is usually operated in a standard shelter to collect a 24-hour sample. The sample is weighed to determine concentration of TSP and is usually analyzed chemically to determine concentration of various inorganic compounds. When EPA first regulated TSP, the National Ambient Air Quality Standard (NAAQS) was stated in terms of SPM with aerodynamic particle size of <100 Fm captured on a filter as defined by the high-volume TSP sampler. Therefore, the high-volume TSP sampler was the reference method. The method is codified in 40CFR50, Appendix B. 1.5 More recently, research on the health effects of TSP in ambient air has focused increasingly on particles that can be inhaled into the respiratory system, i.e., particles of aerodynamic diameter of <10 Fm. These particles are referred to as PM10. It is now generally recognized that, except for toxic materials, it is this PM10 fraction of the total particulate loading that is of major significance in health effects. The reference method for PM10 is codified in 40CFR50, Appendix J and specifies a measurement principle based on extracting an ambient air sample with a powered sampler that incorporates inertial separation of PM10 size range particles and collection of these particles on a filter for a 24-hour period. Again, the sample is weighed to determine concentration of PM10 and is usually analyzed chemically to determine concentration of various inorganic compounds. Method IO-3.3 Chapter IO-3 X-Ray Analysis Chemical Analysis Page 3.3-2 Compendium of Methods for Inorganic Air Pollutants June 1999 1.6 Further research now strongly suggests that atmospheric particles commonly occur in two distinct modes, the fine (<2.5 µm) mode and the coarse (2.5 to 10.0 Fm) mode. The fine or accumulation mode (also termed the respirable particles) is attributed to growth of particles from the gas phase and subsequent agglomerization, whereas the coarse mode is made up of mechanically abraded or ground particles. Because of their initially gaseous origin, the fine range of particle sizes includes inorganic ions such as sulfate, nitrate, and ammonium as well as combustion-form carbon, organic aerosols, metals, and other combustion products. Coarse particles, on the other hand, normally consist of finely divided minerals such as oxides of aluminum, silicon, iron, calcium, and potassium. Samplers which separate SPM into two size fractions of 0-2.5 µm and 2.5-10 µm are called dichotomous samplers. In 1997, the EPA promulgated a new standard with fine particles. The new PM2.5 standard replaced the previously NAAQS for PM10. 1.7 Airborne particulate materials retained on a sampling filter, whether TSP, PM10, PM2.5, or dichotomous size fractions, may be examined by a variety of analytical methods. This method describes the procedures for XRF analysis as the analytical technique. The XRF method provides analytical procedures for determining concentration in ng/m3 for 44 elements that might be captured on typical filter materials used in fine particle or dichotomous sampling devices. With the sample as a thin layer of particles matrix effects substantially disappear so the method is applicable to elemental analysis of a broad range of particulate material. The method applies to energy dispersive XRF analysis of ambient aerosols sampled with fine particle (<2.5 µm) samplers, dichotomous and VAPS (versatile air pollution sampler) samplers with a 10 µm upper cut point and PM10 samples. 1.8 The analysis of ambient aerosol samples captured on filterable material should be performed by a scientist that has been trained in energy dispersive x-ray fluorescence spectroscopy and its associated data processing system. The training should be performed by a scientist with an advance degree in the physical sciences with a minimum of 5 years experience in x-ray spectroscopy. 2. Applicable Documents 2.1 ASTM Documents • D4096 Application of High Volume Sample Method For Collection and Mass Determination of Airborne Particulate Matter. • D1356 Definition of Terms Related to Atmospheric Sampling and Analysis. • D1357 Practice For Planning the Sampling of the Ambient Atmosphere. Chapter IO-3 Method IO-3.3 Chemical Analysis X-Ray Analysis June 1999 Compendium of Methods for Inorganic Air Pollutants Page 3.3-3 2.2 U.S. Government Documents • U.S. Environmental Protection Agency, Quality Assurance Handbook for Air Pollution Measurement Systems, Volume I: A Field Guide for Environmental Quality Assurance, EPA-600/R-94/038a. • U.S. Environmental Protection Agency, Quality Assurance Handbook for Air Pollution Measurement Systems, Volume II: Ambient Air Specific Methods (Interim Edition), EPA-600/R-94/038b. • "Reference Method for the Determination of Particulate Matter in the Atmosphere," Code of Federal Regulations, 40 CFR 50, Appendix B. • "Reference Method for the Determination of Particulate Matter in the Atmosphere (PM10 Method)," Code of Federal Regulations, 40 CFR 50, Appendix J. • "1978 Reference Method for the Determination of Lead in Suspended Particulate Matter Collected From Ambient Air." Federal Register 43 (194):46262-3. • Test Methods for Evaluating Solid Waste, Method 9022, EPA Laboratory Manual, Vol. 1-A, SW-846. 2.3 Other Documents • Kevex XRF TOOLBOX II Reference Manual • Kevex 771-EDX Spectrometer User's Guide and Tutorial 3. Summary of Method [Note: This method was developed using the Kevex spectrometer. EPA has experience in the use of the Kevex spectrometer associated with various field monitoring programs involving analysis of filterable particulate matter for metals over the last two decades. The use of other manufacturers of x-ray spectrometers should work as well as long as the quality assurance and quality control specifications identified in Sections 12 through 14 of Method 10-3.3 are met. However, modifications to Compendium Method IO-3.3 procedures may be necessary if another commercial x-ray spectrometer is used.] The method described is x-ray fluorescence applied to PM10, fine (<2.5 µm) and coarse (2.5-10 µm) aerosols particles captured on membrane filters for research purposes in source apportionment. The samplers which collect these particles are designed to separate particles on their inertial flow characteristics producing size ranges which simplify x-ray analysis. The instrument is a commercially available Kevex EDX-771 energy dispersive x-ray spectrometer which utilizes secondary excitation from selectable targets or fluorescers and is calibrated with thin metal foils and salts for 44 chemical elements. Spectra are acquired by menu-driven procedures and stored for off-line processing. Spectral deconvolution is accomplished by a least squares algorithm which fits stored pure element library spectra and background to the sample spectrum under analysis. X-ray attenuation corrections are tailored to the fine particle layer and the discrete coarse particle fraction. Spectral interferences are corrected by a subtractive coefficient determined during calibration. The detection limits are determined by propagation of errors in which the magnitude of error from all measured quantities is calculated or estimated as appropriate. Data are reported in ng/m3 for all samples. Comprehensive quality control measures are taken to provide data on a broad range of parameters, excitation conditions and elements. Method IO-3.3 Chapter IO-3 X-Ray Analysis Chemical Analysis Page 3.3-4 Compendium of Methods for Inorganic Air Pollutants June 1999 4. Significance Chapter IO-3 Method IO-3.3 Chemical Analysis X-Ray Analysis June 1999 Compendium of Methods for Inorganic Air Pollutants Page 3.3-5 4.1 The area of toxic air pollutants has been the subject of interest and concern for many years. Recently the use of receptor models has resolved the elemental composition of atmospheric aerosol into components related to emission sources. The assessment of human health impacts resulting in major decisions on control actions by federal, state and local governments are based on these data. 4.2 Inhalable ambient air particulate matter (<10 µm) can be collected on Teflon® filters by sampling with a dichotomous sampler and analyzed for specific metals by X-ray fluorescence. The dichotomous sampler collects particles in two size ranges - fine (<2.5 µm) and coarse (2.5-10 µm). The trace element concentrations of each fraction are determined using the nondestructive energy dispersive X-ray fluorescence spectrometer. 4.3 The detectability and sensitivity of specific elements may vary from instrument to instrument depending upon X-ray generator frequency, multichannel analyzer sensitivity, sample interferences, etc. 5. Definitions [Note: Definitions used in this document are consistent with ASTM Methods. All pertinent abbreviations and symbols are defined within this document at point of use.] 5.1 Accuracy. The agreement between an experimentally determined value and the accepted reference value. 5.2 Attenuation. Reduction of amplitude or change in wave form due to energy dissipation or distance with time. 5.3 Calibration. The process of comparing a standard or instrument with one of greater accuracy (smaller uncertainty) for the purpose of obtaining quantitative estimates of the actual values of the standard being calibrated, the deviation of the actual value from a nominal value, or the difference between the value indicated by an instrument and the actual value. 5.4 10 µm Dichotomous Sampler. An inertial sizing device that collects suspended inhalable particles (<10 µm) and separates them into coarse (2.5-10 µm) and fine (<2.5 µm) particle-size fractions. 5.5 Emissions. The total of substances discharged into the air from a stack, vent, or other discrete source. 5.6 Filter. A porous medium for collecting particulate matter. 5.7 Fluorescent X-Rays (Fluorescent Analysis). Characteristic X-rays excited by radiation of wavelength shorter than the corresponding absorption edge. 5.8 Inhalable Particles. Particles with aerodynamic diameters of <10 µm which are capable of being inhaled into the human lung. 5.9 Interference. An undesired positive or negative output caused by a substance other than the one being measured. Method IO-3.3 Chapter IO-3 X-Ray Analysis Chemical Analysis Page 3.3-6 Compendium of Methods for Inorganic Air Pollutants June 1999 5.10 Precision. The degree of mutual agreement between individual measurements, namely repeatability and reproducibility. 5.11 Standard. A concept that has been established by authority, custom, or agreement to serve as a model or rule in the measurement of quantity or the establishment of a practice or procedure. 5.12 Traceability to NIST. A documented procedure by which a standard is related to a more reliable standard verified by the National Institute of Standards and Technology (NIST). 5.13 Uncertainty. An allowance assigned to a measured value to take into account two major components of error: (1) the systematic error, and (2) the random error attributed to the imprecision of the measurement process. 5.14 Chi-square. A statistic which is a function of the sum of squares of the differences of the fitted and measured spectrum. 5.15 Fluorescer. A secondary target excited by the x-ray source and in turn excites the sample. 5.16 FWHM. Full width at half maximum, a measure of spectral resolution. 5.17 NIST. National Institute of Standards and Technology. 5.18 Shape. The actual shape of a background corrected pulse height spectrum for an element. 5.19 SRMs. Standard reference materials. 5.20 Teflo®. Trade name of a Teflon filter. 5.21 Unknown. A sample submitted for analysis whose elemental concentration is not known. 5.22 XRF. X-ray fluorescence. 6. Description of Spectrometer The x-ray analyzer is a Kevex EDX-771 energy dispersive spectrometer with a 200 watt rhodium target tube as an excitation source. The machine has multiple modes of excitation including direct, filtered direct, and secondary which utilizes up to 7 targets or fluorescers. To minimize radiation damage to delicate aerosol samples only the secondary mode is used. Table 1 provides a listing of the fluorescers and the elements which they excite associated with energy dispersive spectrometers. Analysis atmospheres are selectable with choices of helium, vacuum or air; helium is used for all targets except Gd where air is employed because it gives a lower background. The detector is cryogenically cooled lithium-drifted silicon with a 5 µm Be window and a resolution of 158 eV at Fe K" and comes with two manually changeable collimators. A 16 position rotating wheel accommodates the samples and provides sample changing. The machine is operated by procedure files (or programs) written in Kevex's proprietary Job Control Language (JCL) which runs in a Windows 3.1 environment and provides setting of the analytical conditions and data acquisition. Using