Laboratory Experiment pubs.acs.org/jchemeduc
Collection, Extraction, and Analysis of Lead in Atmospheric Particles Kathlyn L. Fillman† and Julie A. Palkendo*,‡ †
Department of Chemistry, University of Rochester, Rochester, New York 14627, United States Department of Physical Sciences, Kutztown University, Kutztown, Pennsylvania 19530, United States
‡
S Supporting Information *
ABSTRACT: Environmental science students are frequently exposed to the analysis of waters, soils, and biological species but have limited experience analyzing the air they breathe. This lab experiment was developed to introduce environmental science majors to a highvolume air sampler, hot-acid extraction, graphite furnace atomic absorption (GFAA) spectroscopy, limits of detection and quantitation, and percent recovery. Lead was specifically chosen for analysis due to the University’s location in Berks County, PA, where two nonattainment areas of this criteria air pollutant are designated by U.S. EPA. Two lab sections determined the concentration of lead in total suspended particulates (TSP) to be 0.0097 ± 0.0009 μg/m3 and 0.0011 ± 0.0012 μg/m3 on two different sampling days in March 2013. Students compared their experimental values to the 2008 National Ambient Air Quality Standard (NAAQS) for lead of 0.15 μg/m3. This experiment provided students an opportunity to think about the chemical composition of atmospheric particles, emission sources, and human health effects. KEYWORDS: Second Year Undergraduate, Upper-Division Undergraduate, Analytical Chemistry, Environmental Chemistry, Laboratory Instruction, Hands On Learning/Manipulatives, Atmospheric Chemistry, Atomic Spectroscopy, Quantitative Analysis
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simultaneous multielement detection, operating costs, and capital expenses. in addition, students learn that the selection of an analytical technique is especially important if accurate and reliable measurements are required, as is the case when enforcing the NAAQS. Recently, this Journal has published interesting lab experiments involving the analysis of cigarette smoke4 and an indirect analysis of metal pollutants from sparkler and space shuttle combustion products;5 however, very few experiments have related air sampling and analysis to the NAAQS for criteria air pollutants.6,7 The experiment described here exposes students to sample collection, extraction, and analysis techniques routinely used by national and state environmental agencies. an external calibration curve was employed, and quality control parameters such as limit of detection (LOD), limit of quantitation (LOQ), and percent recovery were assessed. students successfully compared experimental lead concentrations to the NAAQS for lead in air.
hen the Environmental Protection Agency (EPA) was founded in 1970, it established the National Ambient Air Quality Standards (NAAQS) for six criteria air pollutants: ground-level ozone, particulate matter (PM), sulfur dioxide, carbon monoxide, nitrogen dioxides, and lead. The air quality trends for each of the air pollutants have improved significantly since the 1990 Amendment of the Clean Air Act. Lead specifically has shown the largest decline, with an 84% decrease in the national average between 1990 and 2010.1 Prior to 2008, the NAAQS for lead was set at 1.5 μg/m3 (quarterly average), and the 2008 NAAQS for lead is 0.15 μg/m3 (rolling 3-month average).2 As a result, there are 22 partial counties in 15 states that are not meeting this lower lead standard.3 Berks County, PA, now contains two nonattainment areas. Kutztown University is located within the Lyons nonattainment area in the vicinity of several lead-acid battery manufacturing plants and a secondary lead smelter. This experiment introduces students in the environmental science program to the sampling and analysis of lead in ambient air, a locally interesting problem. the possible use of a variety of atomic spectroscopy techniques for metal analysisflame atomic absorption (AA), graphite furnace atomic absorption (GFAA), and inductively coupled plasma (ICP)allows students to compare and contrast instrument capabilities such as detection limits, ease of automation, single-element versus © 2013 American Chemical Society and Division of Chemical Education, Inc.
Published: December 20, 2013 590
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Laboratory Experiment
Analysis
EXPERIMENTAL OVERVIEW
Students placed their samples (filter blank, unspiked, and spiked) into the autosampler tray of a Varian GTA 110 graphite furnace attached to a Varian 220 FS atomic absorption (AA) spectrometer and logged their sample information into the instrument control software data table. The autosampler was programmed to prepare standard lead solutions at concentrations of 0, 4, 8, 16, 20, 32, and 50 ppb lead from a 100.0 ppb working standard. Standards were analyzed in triplicate, and student samples were analyzed one time each at a wavelength of 217.0 nm. The total analysis time was about 2 h. As the instrument injected standards and samples, the instructor pointed out the automated progress through the temperature program to small student groups. Other important GFAA components were highlighted, such as lamp selection and alignment through the graphite tube and the autosampler operation. The complete data set was compiled by the instructor and made available to students online. Students prepared individual lab reports, which included analysis of limits of detection and quantitation, percent recovery, Pb concentrations in extracts, and mass of Pb in the extracted TSP (see the Supporting Information). Alternatively, simultaneous multielement analysis could be performed on the extract using inductively coupled plasmaoptical emission spectroscopy (ICP-OES) or mass spectrometry (ICP-MS) in lieu of GFAA.11 Our advanced analytical students used anodic stripping voltammetry (ASV) with a thin Hg film on a glassy carbon electrode to quantify Pb, Cu, Cd, and Zn in the filter extracts.12,13
Sample Collection
Each lab section of 13−14 students worked with the instructor to install an 8 × 10 in. glass fiber filter (Whatman EPM 2000) on a Tisch Environmental, Inc. model 5170 V high-volume air sampler designed specifically to collect total suspended particulates (TSP). Although access to this specialized air monitoring equipment may be unavailable at many universities, a simple, home-built system is relatively easy to construct as previously published in this Journal.8 During the filter installation, the instructor demonstrated how to properly secure the filter as well as how to use a manometer, timing devices, and the sampler pump (see the Supporting Information). Each lab section collected a 24 h sample. Removal of the filter after collection was performed by the instructor and student volunteers. Extraction
The steps used to extract soluble lead from the collected TSP are illustrated in Figure 1. The reference method was modified
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HAZARDS During the extraction, students must wear appropriate personal protective equipment, safety glasses and nitrile gloves. The digestion acid is composed of 2% and 4% trace metal grade hydrochloric and nitric acids (Fisher Scientific), respectively. When heating the digestion acid, the cap of the centrifuge tube should be loosened so as to avoid pressurizing the tube, and the hot water bath must be kept in a fume hood. After digestion, the tube should be cooled before addition of deionized water. The lead standard in dilute nitric acid (used to spike the sample) may cause slight irritation of the skin and eyes. Hazards related to lead exposure are minimal at these low concentrations; however, safety glasses and gloves are still mandatory.
Figure 1. Extraction of soluble lead from the collected TSP. (A) Filter strip is cut using a plastic template. (B) Digestion acid is added to the folded filter strip. (C) The digestion apparatus. (D) The addition of deionized water. (E) The tube is manually shaken. (F) The tube is centrifuged. Finally, (G) the supernatant is transferred to autosampler cups for analysis.
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slightly to complete it during a 3 h lab period.9,10 Student pairs cut a 1 × 2 in. strip from the filter using a plastic template. The strip was then carefully folded and placed into the bottom of a 15 mL polypropylene centrifuge tube. Digestion acid prepared as a 2% hydrochloric acid and 4% nitric acid mixture (by volume) was added, and the filter was digested in a hot water bath at 90 °C for 50 min. After cooling, deionized water was added, and the centrifuge tube was shaken vigorously to break up the filter. The sample was then centrifuged (Fisher Scientific Centrific model 228) for 20 min at 3000 rpm. After resting on the benchtop, less than 1 mL aliquots of the supernatant were transferred to GFAA autosampler cups. One sample remained unspiked, and a second sample was spiked with a known volume of 100.0 ppb lead standard. Students also prepared a blank filter (no collected TSP) using the same extraction procedure to determine the quantity of lead present within the filter itself. The sample preparation took students slightly less than 2 h.
RESULTS AND DISCUSSION The concentrations of lead extracted from a 24-h sample of TSP from Kutztown, PA on March 30, 2013 are summarized in Table 1. All measured concentrations were well above the LOD and LOQ of 1.3 and 1.8 ppb, respectively. The relative precision of the class data was very good for the filter blank, unspiked, and spiked samples at 12%, 7.6%, and 8.5%, respectively, indicating that lead in the TSP was uniformly distributed across the filter area. Percent recoveries ranged from 60−123% in this lab section. Many students were surprised that the filter medium contained analyte, prompting some students to ask if other filters were available that contained less lead. The Whatman EPM 2000 filter used in this experiment is the standard filter used by U.S. EPA. The average lead concentration of the filter blank was subtracted from the lead concentration in each unspiked sample before calculating the concentration of lead 591
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Laboratory Experiment
equipment and were prompted to think critically about the composition of the air they breathe.
Table 1. Example Student Data of the Extracted Lead in the Filter Blank, Unspiked Sample, and Spiked Sample group 1 2 3 4 5 6 7 x̅ ± s %RSD
Pb in filter blank (ppb) 10.9 8.6 8.2 9.6 7.5 9.0 8.8 8.9 ± 1.1 12%
Pb in unspiked samplea (ppb) 63.2 70.1 61.4 62.1 55.2 61.0 57.9 61.6 ± 4.7b 7.6%
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Pb in spiked samplea (ppb)
ASSOCIATED CONTENT
* Supporting Information S
86.3 90.1 74.0 74.2 79.9 75.5 73.6 79.1 ± 6.7 8.5%
Student handout; instructor notes. This material is available via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*J. A. Palkendo. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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a
The TSP sample was collected on March 30, 2013. The values reported here account for a 1:1 dilution of the extraction solution. b Concentration before subtraction of the filter blank.
ACKNOWLEDGMENTS We thank Gavin L. Biebuyck at Liberty Environmental, Inc., for his discussions regarding air quality in Berks County and help with the air monitoring equipment. We also wish to thank the students in the spring 2013 courses of CHM/ENV220 and CHM340 for their participation and valuable feedback in this lab experiment.
per volume of air sampled. From the Table 1 data, the average lead in air concentration was determined to be 0.0097 ± 0.0009 μg/m3. Students were asked to compare the experimental value to the 2008 NAAQS for lead of 0.15 μg/m3, assuming that the value would be similar to a three-month average. The students were shocked that the experimental value was significantly lowered than the NAAQS despite the rather dark gray color of the filter paper after TSP collection. Figure 2 shows an example 1 × 2 in. strip cut from a blank filter, the filter sample collected on March 30, 2013, as well as a
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REFERENCES
(1) Air Trends: Lead. http://www.epa.gov/airtrends/lead.html (accessed Dec 2013). (2) National Ambient Air Quality Standards (NAAQS). http://www. epa.gov/air/criteria.html (accessed Dec 2013). (3) Area Designations for 2008 Lead Standards http://www.epa.gov/ leaddesignations/2008standards/index.html (accessed Dec 2013). (4) Gonzalez-Ruiz, V.; Martin, M. A.; Olives, A. I. An Easily Built Smoking Machine for Use by Undergraduate Students in the Determination of Total Particulate Matter and Nicotine in Tobacco Smoke. J. Chem. Educ. 2012, 89 (6), 771−775. (5) Bowden, J. A.; Nocito, B. A.; Lowers, R. H.; Guillette, L. J.; Williams, K. R.; Young, V. Y. Environmental Indicators of Metal Pollution and Emission: An Experiment for the Instrumental Analysis Laboratory. J. Chem. Educ. 2012, 89 (8), 1057−1060. (6) Medhurst, L. J. FTIR Determination of Pollutants in Automobile Exhaust: An Environmental Chemistry Experiment Comparing ColdStart and Warm-Engine Conditions. J. Chem. Educ. 2005, 82 (2), 278− 281. (7) Mang, S. A.; Walser, M. L.; Nizkorodov, S. A.; Laux, J. M. Measurement of Ozone Emission and Particle Removal Rates from Portable Air Purifiers. J. Chem. Educ. 2009, 86 (2), 219−221. (8) Rockwell, D. M.; Hansen, T. Inventory Control: Sampling and Analyzing Air Pollution: An Apparatus Suitable for Use in Schools. J. Chem. Educ. 1994, 71 (4), 318. (9) Determination of Lead Concentration in Ambient Particulate Matter by Inductively Coupled Plasma Optical Emission Spectrometry, EQL0592−086; PA Dept. of Environmental Protection: Harrisburg, PA, 2008. (10) Compendium Method IO-3.1 Selection, Preparation and Extraction of Filter Material; U.S. Environmental Protection Agency: Cincinnati, OH, 1999. (11) Compendium Method IO-3.4 Determination of Metals in Ambient Particulate Matter using Inductively Coupled Plasma (ICP) Spectroscopy; U.S. Environmental Protection Agency: Cincinnati, OH, 1999. (12) Determination of Zinc, Cadmium, Lead and Copper by Anodic Stripping Voltammetry using Carbon Electrodes, Application Bulletin No. 254/1 e; Metrohm AG: Switzerland. (13) Suwannasom, P.; Ruangviriyachai, C. Simultaneous Quantification of Cd, Cu, Pb, and Zn in Thai Fermented Food by DPASV with a Microwave Digestion. Int. Food Res. J. 2011, 18 (2), 803−808.
Figure 2. Filter strips from (A) blank filter, (B) TSP sample collected on March 30, 2013, and (C) TSP sample collected on March 28, 2013.
strip from a filter sample collected on March 28, 2013. Darker shades of gray are indicative of increased TSP concentrations but not necessarily of an increased lead in air concentration. In this case, the light gray filter from March 28, 2013 also had a lower lead in air concentration of 0.0011 ± 0.0012 μg/m3. The large standard deviation indicates that the lead in the TSP was not uniformly distributed over the filter area, which typically occurs with low TSP concentrations. The overall results for both samples caused the students to question the bulk chemical makeup of the particles because lead contributed such a small mass from the total volume of air despite being located within a lead nonattainment area.
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CONCLUSIONS Although many lab experiments in our environmental science curriculum involve analyses of waters, soils, sediments, plants, and animal tissues, this lab experiment provided an opportunity to analyze ambient air. Over 85% of the students executing this experiment found it to be interesting or very interesting, and they appreciated learning the chemical extraction and analysis techniques within the context of their environmental science major. Students gained exposure to standard methods and 592
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