(5)J. Dingman, Jr., S. Siggia. C. Barton, and K. B. Hitchcock. Anal. Chem., 44, 1351 (1972). (6)W. A. Aue and C. R. Hastings, J. Chromatogr..42, 319 (1969). (7)H. H. Weetall. Biochim. Biophys. Acta, 212, 1, (1970).
ACKNOWLEDGMENT Special thanks are given to Richard Cortney, Ames Laboratory summer trainee, for preparing the resins used.
LITERATURE CITED (1)"Standard Methods for the Examination of Water and Wastewater", 13th ed.,1971,p 179. (2)G. B. Harper, Anal. Chem., 47, 348 (1975). (3)D . E. Leyden and G. H. Luttrell, Anal. Chem., 47, 1612 (1975). (4)D . E. Leyden, G. H. Luttrell, and T . A. Patterson, Anal. Lett., 8, 51 (1975).
(8) R.
E. Courtney, Ames Laboratory ERDA. Ames Iowa, unpublished work,
1975. (9)Ref. 1. p 164. (IO)Ref. 1, p 189.
RECEIVEDfor review October 24, 1975. Accepted December 1, 1975.
Lead Determination in Airborne Particulate Matter by Proton Activation Analysis Georges Desaedeleer,' Claude Ronneau, and Desire Apers Universite de Louvain, Laboratoire de Chimie lnorganique et Nucleaire, 2,chemin du Cyclotron, B- 13~8-Louvain-la-Neuve,Belgique
Proton activation analysis has been applied to determine lead concentrations in airborne particulate matter collected on filter papers. 204Biradioactivity, produced by 40-50 MeV proton activation via 208Pb(p,3n), 207Pb(p,4n), 208Pb(p,5n) reactions, is used to identify and measure trace amounts of lead. Up to 40 samples are bombarded simultaneously for a half-hour period. The 374-KeV y ray is usually used to identify lead; however, y rays above the annihilation radiation, as the 899 KeV, are sometimes more suitable. Counting times range from 5 to 50 min per sample. Under reasonable irradiation and counting conditions, and without chemical separations, sensitivities of less than 1 ng/cm2 are currently obtained.
Lead in air is globally due to automotive emissions (1-4). Locally, other sources may also be prevalent (4-6). The physical and chemical properties of leaded aerosol are defined through their emission sources. These physical and chemical properties, as well as the total concentrations, should be taken into account to determine the potential toxicity of the aerosol ( I , 7). I t should be noted that there is still a lack of agreement concerning the toxicity of continuous low exposure to leaded aerosol. This is in part due to the variations with time and location in both total concentration and size distribution (8). In order to study the toxicity of leaded aerosol, one should have the best information on the exposure of humans to airborne lead and therefore take into account all these variations (9). This, however, requires a knowledge of the occurrence of lead in air that can be analyzed over short periods of time. Such analyses require high sensitivity techniques. Irradiation techniques using accelerator beams are very suitable for these high sensitivities. Furthermore, the sensitivity reached also allows considerable simplification of the air sampling devices, and therefore better air monitoring can be achieved (10). Lead analysis in atmospheric particulate matter is currently performed by flame and flameless atomic absorption (11-13), anodic stripping voltametry (14), mass spectrometry ( 1 5 ) ,x-ray fluorescence ( 1 6 ) ,and particle-induced x-ray emission (17, 18). 3He activation analysis has also recently been applied (19).Other activation techniques were used to determine lead in various materials, e.g. thermal and fast 572
ANALYTICAL CHEMISTRY, VOL. 48,
NO. 3,
MARCH 1976
neutron activation (20, 21 ), photon activation (22), protons and deuteron activation (23,24), and 4He activation (25). Low energy, 20 MeV, proton activation allows lead determination down to the nanogram levels (23).206Pb(p,n)and 207Pb(p,2n) reactions induce 206Biradioactivity. However, these levels are reached only under prolonged irradiation and counting conditions, and only after chemical separation of the radioisotopes. On the contrary, in the method presented here, irradiations are performed with more energetic protons. These protons produce 204Biradioactivity by means of *OGPb(p,3n), 207Pb(p,4n),and 208Pb(p,5n) reactions, all having a cross section close to 1 barn (28). Because of its shorter half-life (Table I), 204Biis much more suitable for the evaluation of minute amounts of lead. Also this half-life is long enough so that a large number of samples-up to 40-can be irradiated simultaneously, and subsequent counting may be achieved, making the method readily carried out on a routine basis.
EXPERIMENTAL Target. Standards are made a) of thin aluminum foils (2.7 mg/ cm2)covered by a lead film ( 2 mg/cm2) by evaporation in vacuum or b) of Whatman 41 cellulose filter paper and Sartorius membrane filters (SM11302) (3-5 mg/cm2) uniformly impregnated with a lead nitrate solution (1pg/cm2). Typical samples consist of 1-10 pg/cm2 of aerosol collected on Whatman or Sartorius filter paper. Irradiations. Irradiations are performed at the cyclotron of Louvain-la-Neuve. In a preliminary step, different sets of standards, each standard being sandwiched between aluminum degrader foils, are irradiated at different energies, 60, 55, 50, and 45 MeV. In the routine procedure, targets are covered on both sides by high-purity thin aluminum foils (1 mg/ cm2) and sandwiched between aluminum rings. In these rings, a hole is drilled, allowing helium circulation to cool the targets. They are maintained and aligned by means of two brass rods which are driven through the holes A (Figure l ) , allowing easy dismounting. Irradiations are done with 50-MeV protons and 1-MAintensity, for 30 min. Together with each set of three samples, several standards interleaved with the samples are irradiated. Counting. Radionuclides are identified by y spectrometry by means of an 80-cm3 Ge(Li) detector and a Northern 4096 channel analyzer coupled with a PDP 11-20 computer. Data acquisition is made in two steps: a) first, on-line with the analyzer, the PDP computer allows a simple treatment of the spectrum and stores it on magnetic tape, and b) second, the magnetic tape is treated by SAMPO (26) on an IBM 370 computer for peak location and area calculation. Samples are counted, without chemical separations, after at least 6-h cooling time in order to reduce the annihilation
I He in
Table Ia. Isotopic Composition of Natural Lead 204 (1.48%)
206 (23.6%)
207 (22.6%) 208 (52.3%)
Table Ib. Decay Characteristics of Bismuth Radioisotopes Induced by Proton Activation I sotope
Half-Life
*
Targets
cwllnq water
4hk-x
0 Ring
__
-
Sandwic.9 rings
y Energies (MeV) and a b u n d a n c e s
203 11.8 h 0.820(0.47) 204 11.2 h 0.899(1.00a) 205 15.3 d 0.703(0.28) 206m 7.8 !.is 0.060(1.00a) 206 6.23 d 0.803(0.33) 207m 0 . 1 8 m s 0.669‘ ’ 207 30. y 0.570(0.98) 208m 2.57 ms 0.510 208 3.7 x l o 5 y 2.615 a Relative abundances.
‘ H e out 1
1.034(0.16) 0.825(0.20) 0.375(0.83a) 0.912(0.23a) 1.766(0.21) 0.988(0.17) 0.881(0.72j 0.713‘ 1.063(0.77) 0.064
He
in
0.516(0.46) 0.932 1.770(0.09) 0.650
Targets holdei
radiation coming from the activity induced in the filter paper. Aluminum foils are removed before counting, to reduce the y spectrum background. Recoiling 204Biatoms are caught in the filter paper, and the upstream aluminum foil did not show a significant interference by *04Biactivity. The 374.7-KeV y ray of 204Biis usually used for lead identifications; the 899.3-KeV is more appropriate in some circumstances, e.g. when the annihilation radiation is still preponderant. Standards and samples are counted as extracted from the sample holder. Characteristic counting times are 5 min for standards and 5 to 50 min for samples, according to the loading. Quantitative analysis is achieved by comparison of the activities in the sample and in the set of standards interleaved with the samples. This allows easy analysis with satisfactory precision, better than 15%, (see Table 111below) without having to consider calculations for energy losses through the stack of samples. Interfering Reactions. Only the *ogBi(p,p5n)204Bireaction may interfere with the Pb(p,xnjZo4Bireactions. This interference is, however, negligible in the present cases because a) the cross section for the interfering reaction is around an order of magnitude smaller ( 2 7 ) and b) typical bismuth concentrations in atmospheric particles are IO3 times lower than lead concentrations. The present method for lead is essentially interference-free.
Flgure 1. Scheme of the target holder use for bombardment of paper filters
RESULTS Analytical Developments. (A) I n a preliminary experiment, t h e shape of t h e excitation function for P b ( p , ~ n ) ~ O * Breactions i was determined. Bell a n d Skarsgard (28) determined the cross section for (p,xn) reactions on the different lead isotopes, for a n energy range from 13 t o 47 MeV. Their data corrected for t h e isotopic composition of natural lead are presented in Figure 2. In order t o determine t h e most favorable irradiation energy for lead activation, irradiation of natural lead standards was achieved at higher energies, 45 t o 60 MeV. Degrader aluminum foils were used to extend the cross-section values t o lower energies, so as to have an idea of t h e shape of t h e excitation function for P b ( p , ~ n ) ~ ~T~hBe iresults . are presented in Figure 2. Error bars are statistical errors at one sigma, and are mainly associated with inhomogeneities in t h e preparation of t h e standard by evaporation. A marked peak appears a t around 47 MeV. This peak is ascribed a) t o t h e 208Pb(p,5n)reaction, occurring on t h e most abundant lead isotope, and b) t o t h e *07Pb(p,4n)reaction, which still has at 47 MeV a large cross section. As a set of 40 samples is irradiated simultaneously for routine analysis, a 50-MeV proton energy was chosen so a t o compensate for t h e energy loss in t h e stack. ( B ) Accuracy. I n order to test our analytical procedure, samples were analyzed by proton activation analysis a n d flameless atomic absorption spectrometry. T h e airborne particulates were collected by filtration on membrane filters using a high-volume sampler (20 m3/h). T h e aerosol was collected over 10 h on a 175 cm2 filter surface, in a
i/ / I
30
/*
,,
x/
40
Proton
Energy ( M e V ) -
50
60
Figure 2. Relative excitation function for the P b ( ~ , x n ) ~reactions ~~Bi on natural lead, Broken lines represent the data of Skarsgard and Bell (28)and the solid line those obtained in the present work
rural area (Perwez) located 35 km southeast of Brussels. A 1 cm2 filter area was submitted t o proton bombardment, and 40 cm2 of the filter were dissolved in nitric acid and subsequently analyzed by flameless atomic absorption. Comparison of t h e results is presented in Table 11. Agreement between t h e methods is usually fairly good, and only for low lead concentration is there a statistically significant difference. Activation analysis presents, among other things, t h e advantage of eliminating analytical uncertainties which result from extensive sample preparation. (C) Precision. Samples were collected in the western suburbs of Brussels and at Louvain-la-Neuve, a rural area 25 km southeast of Brussels, by a hi-volume sampler (20 m3/h) and were analyzed on a statistical basis. From the 175 cm2 filter area, six discs of 2.5-cm diameter were exposed t o t h e 1 cm2 cyclotron proton beam. Results of t h e analysis are presented in Table 111. T h e precision is better than 15%. It has to be noted that the variation may include non-uniform sample collection on t h e 175 cm2 filter area. ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
573
Table 11. Lead Concentration at Perwez, November 1973, Determined by Proton Activation and Flameless Atomic Absorption Pb, v g / m 3 Date
Activation
Atomic absorption
31110173 1/11/73 2/11/73 3/11/73 4/11/73 5/11/73 6/11/73 7/11/73 8/11/73 9/11 17 3 10/11/73 11/11/73 12111173 13/11/73 14/11/73 15/11/73 16/11/73 1711157 3 18/11/73
0.578 0.967 0.878 0.470 0.339 0.047 0.330 0.796 0.310 0.096 0.079 0.097 0.597 0.067 0.113 0.097 0.245 0.470 0.109
0.592 0.936 0.764 0.452 0.242 0.070 0.254 0.651 0.219 0.159 0.125 0.113 (1.36) 0.097 0.118 0.117 0.270 0.575 0.118
P b a c t . / P b a t . abs.
0.976 1.03 1.15 1.04 1.40 0.67 1 1.30 1.22 1.42 0.604 0.632 0.858 0.691 0.957 0.829 0.907 0.81 7 0.927 0.968 t 0.252
Table.111. Reproducibility of Results Obtained in Proton Activation of Lead Sampling
Pb W m 3 )
Brussels ( a ) February 1973 Brussels ( b ) February 1973 Louvain-la-Neuve April 1 9 7 3
1.74; 1.65; 1.98; 1.57; 1.80; 1.82 0.57; 0.59; 0.64; 0.63; 0.48; 0.54 0.064; 0.072; 0.083; 0.061; 0.071; 0.059; 0.060 0.107; 0.098; 0.122; 0.098; 0.115; 0.099
Louvain-la-Neuve May 1973
Pbav.
uPb
1.76 i 0.14 0.58 = 0.06 0.067
i
0.009
0.107
i
0.010
Figure 3. Location of sampling stations as compared to the local
emission sources subjected to the emissions from a freeway. Lead concentrations for samples collected from April 1972 to December 1973 a t three of these stations are reported. During this period, in February 1973, a new freeway (E40) was opened to automobile traffic, so that the contribution of the freeway to earlier lead concentrations can be evaluated. For each wind direction, a mean lead value and the standard deviation around this value are reported. These variations are due to the different meteorological conditions encountered during the sampling periods (32, 32). I t has to be noted that under some meteorological conditions, the same concentrations are encountered a t Station 1 and a t Station 4, meaning that meteorological conditions are a predominant factor in order to assess the pollution on a site.
CONCLUSION
Routine Analysis of Lead in Airborne Particulate Matter. Until now, about 500 lead determinations have been successfully carried out in filters loaded with small quantities of aerosol. The purpose is to determine the contribution of freeway emissions to ambient lead concentrations in a rural area. Five pollution stations are installed in the vicinity of Louvain-la-Neuve (Figure 3). Airborne particulate matter is collected by filtration through 25-mm diameter Whatman filters, with a low flow rate of 1 l./min. Only 1 cm2 of these filters is subjected to proton bombardment. Extensive data analysis is reported in the literature ( I , 29-32), and Table IV presents typical values which are indicative of the pollution levels of lead in a rural area
(A) The method is particularly sensitive and suitable for routine analysis. Nanogram amounts of lead on a 1 cm2 area are easily detected under bombardment and counting conditions as previously described. This sensitivity can easily be improved upon by longer irradiations and counting times, which will increase the induced and detected 204Bi activities. Also the half-life of 204Biis long enough so that, if required, a chemical separation can easily be performed. This separation will increase the sensitivity by lowering the background of the y-ray spectrum. The precision of the analysis is on the order of 15%.This can also be improved: (a) by taking into consideration the variation in the induced activity due to the energy loss of the protons going through the stack of samples, (b) by controlling the homo-
Table IV. Mean Lead Concentrations at Three Locations Near Louvain-la-Neuve, Belgium, and Variations with Wind Direction Lead ( n p j m 3 ) Station 1 Before0
N-NE NE-E E-SE SE-S
Station 4 .4fter0
2 1 6 + 48 1470 i 315 5 3 6 1 380 1181 z 577 628 t 348 1 3 8 9 i 809 291 i 226 4 3 4 ~208 s-SW 217 i 180 1 9 3 t 186 SW-W 1 2 5 - 104 368 I 307 W-NW 6 0 2 1 258 2 6 0 3 111 NW-N 1 8 5 i 112 a Before and after the opening of freeway E40.
574
Before0
272 i 430 i 236i 115 i 191 z 144 t 145 i 105:
ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
174 486 115 24 173 62 18 59
Station 3 After0
428 59 2 327i 237 176 = 147 t 273 = 187
147 110
143 209
Before0
67 = 150i 367 117 z 134t 383 = 369 i 3451
25 93 133 110
140 83 142
Aftera
616 i 3121 283i 53t 58k 84 i 325i
164 133 146 25 30 42 100
geneity of the standards, and (c) by increasing the counting statistics. Because of the features of activation analysis one may wish to reach highly sensitive and highly precise determinations in different material. The designed target holder-allowing the simultaneous irradiation of 40 samples-makes routine analysis readily performed by limiting the time consumption of a large cyclotron. T h e method allows analysis of homogeneous samples, as is the case for air filters, or of small inhomogeneous samples, e.g., samples t h a t can be covered by the beam area. Furthermore, the method as suitable for thin samples can also be applied to determine concentrations in thick samples. ( B ) Charged particle activation allows lead determinations in aerosol samples from less than 0.1 m3 of air of remote areas. Typical sensitivities achieved during our routine analysis are 1 ng/cm2, allowing lead determination in air volumes as low as 0.1 m3/cm2. This is particularly interesting for air pollution monitoring. Large air samplers are no longer required for this analytical technique, and samplers having low flow rate and small collection area (1cm2) can be used instead ( 1 0 ) .The analysis is nondestructive, so t h a t the samples can be reused for other purposes. Finally, other elements have been identified in the y-ray spectrum. They were, however, not analyzed quantitatively. There are As, Sn, Se, Cu, Zn, Mn, Fe, Ni, Sr, Cr, and Na. By changing the counting conditions, other elements could be seen, e.g., Ca, Sc, Ti, V, Co, Br, Ag, and Cd. Care, however, has to be taken on interfering reactions on lower 2 elements. The wide variety of elements seen makes this method very attractive for multielement analysis. Furthermore, lead isotopic analysis using prot.on activation could also be performed.
ACKNOWLEDGMENT We are indebted to the cyclotron staff and P. Macq for providing irradiation facilities. We also express appreciation to N. Jacob and J. Ligot for their valuable assistance in the laboratory analysis, and to J. Cara and P. Nemegeer for their very valuable technical aids. J. W. Winchester is acknowledged for his comments and review of the manuscript.
LITERATURE CITED (1) Georges Desaedeleer, Ph.D. Dissertation, Louvain University, October 1974. (2) M. Murozumi. T. J. Chovd, and C. Patterson, Geochim. Cosmochim. Acta. 33, 1247 (1969).
(3) T. J. Chow, K. W. Bruland, K. Bertine, A. Soutar, M. Koide, and E. D. Goldberg, Science, 181, 551 (1973). (4) "Airborne Lead in Perspective", National Academy of Sciences, Washington, D.C., 1972. (5) W. U. Auk, R . G. Senechal and W. E. Erlebach, Environ. Sci. Techno/., 4, 305 (1970). (6) M. B. Rabinowitz and G. W. Wetherill, Environ. Sci. Techno/., 6, 705 (1972). (7) Georges Desaedeieer and J. W. Winchester, Environ. Sci. Technol., 9, 971 (1975). (8) G. G. Desaedeleer, J. W. Winchester, R. Akselsson, K. A. Hardy, and J. W. Nelson, Trans. Am. Nucl. Soc., Suppl. 3, 21, 36 (1975). (9) G. G. Desaedeleer, J. W. Winchester and R. Akselsson, International Conference on Heavy Metals in the Environment, Toronto, 27-31 October. 1975. D. B1. J. W.Nelson, E. Jensen, G. Desaedeleer, R . Akselsson, J. W. Winchester, Adv. X-ray Anal., 19, in press. J. L. Moyers, W. H. Zoller, R. A. Duce, and G. L. Hoffman, Environ. Sci. Technol., 6, 68 (1972). E. L. Jernigan, B. J. Ray, and R . A. Duce, Atmos. Environ., 5, 881, 1971. R . M. Daines, Environ. Sci. Technol., 4, 318 (1970). J. W. Winchester, W. H. Zoiier, R . A. Duce, and C. S. Benson, Atmos. Environ., 1 , 105 (1967). T. J. Chow, J. L. Earl, and C. F. Bennet, Environ. Sci. Techno/., 3, 737 (1969) ~ ~ , C. S. Martens, J. J. Wesolowski, R . Kaifer and W. John, Atmos. Environ., 7, 905 (1973). T. B. Johansson, R . E. Van Grieken, J. W. Nelson, and J. W. Winchester, Anal. Chem., 47, 855 (1975). T. A. Cahill, "Cyclotron Analysis of Atmospheric Contaminants", Report of Crocker Nuclear Laboratory, University of California, Davis, Calif., 1972. B. Parsa and S. S. Markowitz, Anal. Chem., 46, 186 (1974). P. Meyers, "Proceedings of the 2nd Conference on Practical Aspects of Activation Analysis with Charged Particles, Liege, 1967", Vol. 1, Euratom, Brussels, p 195. G. W. Reed, K. Kogoshi, and A. Turkevich, "Proceedings of the 2nd International Conference on the Peaceful Uses of Atomic Energy, Geneva, 1958", Vol. 28, paper 953, United Nations, N.Y.. p 486. E. A. Schweikert and Ph. Albert. "Radiochemical Methods of Analysis", Vol. 1, IAEA, Vienna, 1965, p 323. E. A. Schweikert, Trans. Am. Nucl. SOC., 13, 58 (1970). D. C. Riddle and E. A. Schweikert, Anal. Chem., 46, 395 (1974). J. C. Cobb, J. Geophys. Res., 69, 1895 (1964). J. R. Routti, "SAMPO. A Fortran IV program for computer analysis of gamma spectra from Ge(Li) detectors, and for other spectra with peaks", University of California, Rept. UCRL-19452, 1969. M. Barbier, "Induced Radioactivity", North Holland, 1969. R. E. Bell and H. M. Skarsgard, Can. J. Phys., 34, 745 (1956). Georges Desaedeleer, Claude Ronneau, and Desire Apers, Progress Report CNEPAC, Vol. 6, Brussels, 1975. Georges Desaedeleer, Environ. Sci. Techno/. (submitted). G. Desaedeleer and E. Schifflers, Atmos. Environ. (submitted). G. Desaedeleer and C. Ronneau, Trans. Am. Nucl. SOC.,Suppl. 3 , 2 1 19 (1975). I
RECEIVEDfor review October 29, 1974. Resubmitted July 10, 1975. Accepted November 12, 1975. The authors gratefully acknowledge the Centre National d'Etude de la Pollution Atmosphkrique par la Combustion for its financial assistance.
Rapid Photochemical Decomposition of Organic Mercury Compounds in Natural Water A. M. Kiemeneij and J. G. Kloosterboer" Philips Research Laboratories, Eindhoven, The Netherlands
A method has been developed for the determination of total mercury in water at concentrations in the ppb range. Decomposition of organo mercurials is carried out by means of ultraviolet radiation of a suitable wavelength from small, low-pressure lamps containing either Zn, Cd, Hg or a mixture of these metals in their cathodes. The formed inorganic mercury is determined in the usual way by cold vapor atomic absorption after reduction of Hg2+ to Hg'. Determinations with and without irradiation make possible separate deter-
mination of total and inorganic mercury, respectively. Irradiation times are approximately 20 min. The "photochemical" analysis of natural water samples is compared with the wet-chemical analysis. The results agree within 4 % at a level of 1 pg/l., even for unfiltrated samples. The photochemical method, which requires a minimum of reagents (only HCI and SnCI2), yields substantially lower blank values than the wet-chemical method.
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