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EDXRF determination of Pb in aerosol samples from Mexico Valley
Radiation Physics and Chemistry 61 (2001) 681–682
EDXRF determination of Pb in aerosol samples from Mexico Valley J. Lartiguea,*, R. Padillab, T. Mart!ıneza, M. Ortaa a
Faculty of Chemistry, National University of Mexico, CU, DF 04510 Mexico City, Mexico b CEADEN, P.O. Box 6122, Havana, Cuba
Abstract Atmospheric pollution in very populated towns is mainly generated from fuel combustion and industrial activity, though in some regions, soil erosion, residues incineration and forest fires contribute appreciably. In the case of Mexico Valley, there exists a permanent additional factorFvolcanic ash whose chemical and physical characteristics represent a serious sample-preparation problem. This paper proposes an analytical procedure based on the energy dispersive X-ray fluorescence method (EDXRF), being quick, reliable and non-destructive, to determine Pb concentration in aerosol samples. A good correlation factor with the atomic absorption (AA) method is obtained. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: Pb concentration; Aerosol samples; EDXRF
1. Antecedents The analysis of environmental samples is performed in a laboratory (LBFQ) operated by the National University of Mexico for the Government of the Federal District. The method used to date to measure Pb concentration in air has been based on the atomic absorption (AA) analysis of atmospheric particles collected on filters, which requires the use of nitric and hydrochloric acids and is time-consuming. Furthermore, the presence of volcanic glass in environmental powder would require additional hydrofluoric acid treatment that complicates the procedure. Two alternative methods, quick and non-destructive, based on EDXRF, have been developed in the LBFQ for Pb analysis. Both of them imply higher limits of detection than the AA method, but they are sensitive enough to quantify onetenth of the maximum permissible concentration of Pb in air. The first one, based on fundamental parameters, was presented at NURT-99 (Lartigue and Padilla, 1999). The second one, based on calibration curves and Compton corrections, is presented in this paper. *Corresponding author. Fax: +52-5622-5232. E-mail address: [email protected] (J. Lartigue).
According to the Mexican Technical Norm, the maximum accepted level for lead concentration in air is 1.5 mg Pb/m3.
2. Experimental procedure Sampling of airborne particulate matter was performed using high volume collecting devices (2160 m3 air/day) on large aerosol filters (800 1000 ). With this arrangement, the maximum daily collected amount of Pb, corresponding to the permissible level, would be around 3200 mg Pb/filter. The average value remains under one-tenth of the same figure and coincides with the quantification limit of the now proposed method (300 mg/filter). Collected aerosols show a high volcanic glass proportion (40%) and a very high content of respirable particles (>75%). This figure is meaningful since contaminants adhere mainly to the smallest particles. The EDXRF spectrometer consists of a Princeton Gamma Tech. (SiLi) detector (resolution=180 eV, Mn Ka) and associated electronics, with a holder to position the 30 m Ci Pu-238 source. Samples were prepared with 200 600 portions of the filters, folded in three, then irradiated for 3000 s (live time). Spectra
0969-806X/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 0 1 ) 0 0 3 7 1 - 1
682
J. Lartigue et al. / Radiation Physics and Chemistry 61 (2001) 681–682
AA and EDXRF methods. The Pb content of 72 samples (by AA) was lower than the limit of quantification of the proposed EDXRF method but, as reported in this way (o0.15 mg Pb/m3), a practical coincidence of results has been found for the AA and EDXRF methods in this rank. However, in order to know the true correlation in the zone of interest (>0.15 mg Pb/m3), Fig. 1 was obtained for the rest of 10 samples. The correlation factor (0.98) and the statistical error (715%) let us confirm the adequacy of the EDXRF method, in this calibration-curve version, for Pb monitoring. Fig. 1. Correlation curve AA–XRF; cient=0.985; error=715%.
correlation
coeffi-
were analysed using the NUCLEUS program (Tennelec, Oak Ridge). Net ROIs were corrected using the scattered source lines method (Jenkins et al., 1981).
3. Results A calibration curve was produced for 59 samples whose Pb concentration had been determined by the AA method. The resulting correlation factor (0.94) and statistical error (711%) permitted us to assume an acceptable reliance for the EDXRF method. Later, a comparison was made for 82 samples analysed by the
Acknowledgements The authors would like to thank J. Flores, M. Barcena, C. Anzures and L.M. Rivas for their useful technical assistance.
References Jenkins, R., Gould, R.W., Gedcke, D., 1981. Quantitative X-ray Spectrometry. Marcel Dekker Inc., New York, pp. 462–464. Lartigue, J., Padilla, R., 1999. EDXRF determination of Pb in aerosol samples from Mexico City. Proceedings of NURT99 Symposium, IAEA-CEADEN, La Habana, Cuba.
EDXRF determination of Pb in aerosol samples from Mexico Valley J. Lartiguea,*, R. Padillab, T. Mart!ıneza, M. Ortaa a
Faculty of Chemistry, National University of Mexico, CU, DF 04510 Mexico City, Mexico b CEADEN, P.O. Box 6122, Havana, Cuba
Abstract Atmospheric pollution in very populated towns is mainly generated from fuel combustion and industrial activity, though in some regions, soil erosion, residues incineration and forest fires contribute appreciably. In the case of Mexico Valley, there exists a permanent additional factorFvolcanic ash whose chemical and physical characteristics represent a serious sample-preparation problem. This paper proposes an analytical procedure based on the energy dispersive X-ray fluorescence method (EDXRF), being quick, reliable and non-destructive, to determine Pb concentration in aerosol samples. A good correlation factor with the atomic absorption (AA) method is obtained. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: Pb concentration; Aerosol samples; EDXRF
1. Antecedents The analysis of environmental samples is performed in a laboratory (LBFQ) operated by the National University of Mexico for the Government of the Federal District. The method used to date to measure Pb concentration in air has been based on the atomic absorption (AA) analysis of atmospheric particles collected on filters, which requires the use of nitric and hydrochloric acids and is time-consuming. Furthermore, the presence of volcanic glass in environmental powder would require additional hydrofluoric acid treatment that complicates the procedure. Two alternative methods, quick and non-destructive, based on EDXRF, have been developed in the LBFQ for Pb analysis. Both of them imply higher limits of detection than the AA method, but they are sensitive enough to quantify onetenth of the maximum permissible concentration of Pb in air. The first one, based on fundamental parameters, was presented at NURT-99 (Lartigue and Padilla, 1999). The second one, based on calibration curves and Compton corrections, is presented in this paper. *Corresponding author. Fax: +52-5622-5232. E-mail address: [email protected] (J. Lartigue).
According to the Mexican Technical Norm, the maximum accepted level for lead concentration in air is 1.5 mg Pb/m3.
2. Experimental procedure Sampling of airborne particulate matter was performed using high volume collecting devices (2160 m3 air/day) on large aerosol filters (800 1000 ). With this arrangement, the maximum daily collected amount of Pb, corresponding to the permissible level, would be around 3200 mg Pb/filter. The average value remains under one-tenth of the same figure and coincides with the quantification limit of the now proposed method (300 mg/filter). Collected aerosols show a high volcanic glass proportion (40%) and a very high content of respirable particles (>75%). This figure is meaningful since contaminants adhere mainly to the smallest particles. The EDXRF spectrometer consists of a Princeton Gamma Tech. (SiLi) detector (resolution=180 eV, Mn Ka) and associated electronics, with a holder to position the 30 m Ci Pu-238 source. Samples were prepared with 200 600 portions of the filters, folded in three, then irradiated for 3000 s (live time). Spectra
0969-806X/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 0 1 ) 0 0 3 7 1 - 1
682
J. Lartigue et al. / Radiation Physics and Chemistry 61 (2001) 681–682
AA and EDXRF methods. The Pb content of 72 samples (by AA) was lower than the limit of quantification of the proposed EDXRF method but, as reported in this way (o0.15 mg Pb/m3), a practical coincidence of results has been found for the AA and EDXRF methods in this rank. However, in order to know the true correlation in the zone of interest (>0.15 mg Pb/m3), Fig. 1 was obtained for the rest of 10 samples. The correlation factor (0.98) and the statistical error (715%) let us confirm the adequacy of the EDXRF method, in this calibration-curve version, for Pb monitoring. Fig. 1. Correlation curve AA–XRF; cient=0.985; error=715%.
correlation
coeffi-
were analysed using the NUCLEUS program (Tennelec, Oak Ridge). Net ROIs were corrected using the scattered source lines method (Jenkins et al., 1981).
3. Results A calibration curve was produced for 59 samples whose Pb concentration had been determined by the AA method. The resulting correlation factor (0.94) and statistical error (711%) permitted us to assume an acceptable reliance for the EDXRF method. Later, a comparison was made for 82 samples analysed by the
Acknowledgements The authors would like to thank J. Flores, M. Barcena, C. Anzures and L.M. Rivas for their useful technical assistance.
References Jenkins, R., Gould, R.W., Gedcke, D., 1981. Quantitative X-ray Spectrometry. Marcel Dekker Inc., New York, pp. 462–464. Lartigue, J., Padilla, R., 1999. EDXRF determination of Pb in aerosol samples from Mexico City. Proceedings of NURT99 Symposium, IAEA-CEADEN, La Habana, Cuba.