Literature Cited Altshuller, A. P., Bufalini, J. J., Photochenz. Photobiol. 4, 97-146 (1965). Altshuller, A. P., Cohen, I. R., Air Water Pollution 7, 787 (1963). Altshuller, A. P., Cohen, I. R., Air Water Pollution 8, 611 (1964). Altshuller, A. P.. Cohen, I. R., Purcell, T. C., Science 150, 1161 (1967). Altshuller, A. P., Kopczynski, S. L., Wilson, D., Lonneman, W., Sutterfield, F. D., 61st Annual Meeting, Air Pollution Control Assoc., St. Paul, Minn., June 1968. Altshuller, A. P., Kopczynski, S. L., Lonneman, W. A.. SCI. TECHNOL. 2, Becker, T. L., Wilson, D. L. ENVIRON. 696 (1968). Bodenstein, M.. Wachenheim, L., Z . Angew Chem. 31, 145 (1918). Bufalini. J. J.. Stephens. E. R., Air Water Pollution 9, 123 (1965). Bufalini. J. J.. Purcell. T. C., Science 150, 1161 (1965). California Department of Public Health, Bureau of Air Sanitation. Berkeley. Calif., "The Oxides of Nitrogen in Air Pollution." January 1966. Cvetanovic. R. J.. J . Air Polllition Control Ascoc. 14, 209 (1964).
Dimitriades, B.: J . Air Pollution Control Assoc. 17, 460 (1967). Glasson, W. A., Tuesday. C. S., J . A m . Chem. SOC.8 5 , 2901 (1963). Johnston, H . S.: Slentz, L. W., J . A m . Chem. SOC.73, 2948 (1951). Leighton, P. A., Physical Chemistry: Vol. IX, Thotochemical Aspects of Air Pollution," Academic Press, New York, 1961. Ripley, D . L.. Clingenpeel, M. M., Hurn, R. W., Air Water Pollzrfion 8, 455 (1964). Stephens, E. R., in "Chemical Reactions in the Lower and Upper Atmosphere." Cadle, R. D., Ed., p. 51, Interscience, New York, 1961. Treacy. J. C.: Daniels, F.. J . ' 4 m . Chem. SOC. 77, 2033 ( 1955). Wayne. I_. G.. "The Chemistry of Urban Atmospheres." Tech. Prog. Rep. 111, Los Angeles Air Pollution Control District. December, 1962. Received for review Airgust 21, 1968. Accepted January 23, 1969. itlention of cornnzercial products does not constitiite endorsement b j the Public Health Service.
Determination of Lead in Airborne Particulates in Chicago and Cook County, Illinois. by Atomic Absorption Spectroscopy Carole D. Burnham, Carl E. Moore, and Eugene Kanabrocki Chemistry Department, Loyola University, Chicago. Ill. 60626 Don M. Hattori City of Chicago, Department of Air Pollution Control. Chicago, Ill.
A simple precise procedure for determining the lead content of suspended particulate samples collected from the air uses atomic absorption spectroscopy. It is necessary to utilize the standard additions technique to overcome matrix effects. Analyses of 38 samples collected in the Chicago and Cook County area on March 31, 1966, as a part of the National Air Sampling Network, yielded values from 0.10 to 3.18 pg. of Pb per cubic meter of air. Results obtained by the referee method of polarography showed substantial agreement with atomic absorption values. Possibilities of employing atomic absorption for the determination of other metals found in suspended particulates are currently being investigated.
A
lthough the field of air pollution is attracting increasing public and scientific attention, there is a notable lack of information on the nature, quantity, and seasonal variations of pollutants in various localities. Without these data, the establishment of sensible legal standards for the prevention and control of atmospheric contamination is difficult. if not impossible. 472 Environmental Science & Technology
It is the purpose of these studies to develop simple, in expensive methods and procedures for the routine determination of metals contained in the particulate matter collected at air sampling stations in widely different environments. Since unique and complex conditions exist at each geographical location, matrix interferences in any given sample are difficult to predict or duplicate. thus posing the need for an analytical technique relatively free from chemical or spectral interferences. The technique of atomic absorption spectroscopy (Walsh, 1955) is an obvious choice for the analysis of many metals. Use of the atomic absorption methodology would allow the small Eow-budget laboratory to evaluate field samples and accumulate data on purely local conditions, in contrast to the large spectrographic equipment which is currently in good use (Keenan and Holtz. 1964) at the larger air pollution labs but which is outside both the budget and technical capabilities of the smaller laboratory. It is always preferable to develop analytical methods using actual field samples, particularly for spectrochemical methods in which matrix effects play a significant role. The present technique was thus evolved using particulate samples obtained on March 31, 1966, at 38 stations located throughout Chicago and Cook County. Ill. These samples were collected routinely and were made available for investigation by the City of Chicago. Department of Air Pollution Control. As a
point of departure it was decided to apply the atomic absorption technique to the determination of lead and to crosscheck the results by a referee method such as polarography. The feasibility of determining lead by atomic absorption spectroscopy has been demonstrated by Dagnall and West (1964) and Chakrabarti, Robinson, et al.; (1966). among others.
Experimental &uipment A Perkin-Elmer Model 303 double-beam spectrophotometer, fitted with a three-slot Boling burner (Boling, 1966) and an automatic null recorder readout accessory. was used for the atomic absorption analyses. Readings in per cent absorption on zero-left recorder paper were obtained from a Sargent Multi-Range recorder on the 0- to 12.5-mv. range using the 2170 A. spectral line and the operating conditions for lead recommended by the manufacturer (Perkin-Elmer Corp.). No measurable scatter was detected at a nonabsorbing line in the 2170 A. spectral region. Most analyses were performed on a scale expansion setting of 1 and a noise suppression of x3; the X 3 scale expansion and X 4 noise suppression were required for determination of the detection and sensitivity limits. The aspiration rate for which optimum results were obtained was 5 ml. per minute. Results obtained by atomic absorption were spotchecked on the E. H. Sargent Model XXI Polarograph with an electrolysis vessel requiring only 5 ml. of sample volume. Sensitivity ranges of 0.010 to 0.003 pa. per mm. and a voltage span of 0 to -2 volts were emploqed.
ensure absorption determinations in the linear range of the calibration curve. The method of standard additions (Willard, Merritt, et al., 1965a) was employed to avoid possible effects on the unique matrix in each sample on the absorption of the lead. To 4.00-ml. aliquots of the diluted solution were added 1.00 ml. of standard lead solutions containing from 0 to 20 pg. of Pb per ml. The absorption readings of these spiked solutions were then obtained and converted to absorbance units, from which the absorbance of a deionized water blank was subtracted. Each absorbance value was then plotted against the corresponding concentration of standard lead in each aliquot, and the lead content of the diluted solution was obtained from the intercept of the linear curve on the concentration axis as shown in Figure 2. Multiplication by the appropriate dilution factors and subtraction of the lead content of the glass-fiber filter extract ( 5 pg. per ml.) yielded the
3
/
cc 0
Standard Lead
/
~
Experimenfal Methods and Resirlrs
Atomic Absorption. STANDARD SOLUTIONS. Standard soltitions containing 0 to 50 pg. per ml. of lead in dilute nitric acid were used to examine the atomic absorption spectroscopy of lead under the operating conditions outlined above. Typical calibration curves (Figure 1) showed linearity in the range of 0 to 20 pg. per ml. of lead corresponding to 0 to 55% absorption or absorbances of about 0 to 0.350. The sensitivity (concentration required to produce 1;: absorption) and detection (concentration that can be determined with joyc certainty) limits were found to be 0.25 and 0.05 pg. per ml. of lead, respectively. Standard deviations determined at several lead concentrations and listed in Table I indicate that the range of 0 to 2 pg. per ml. shotild be avoided when precision corresponding to a coefficient of variation of less than 5Yc is required. PROCEDURE FOR ANALYSISOF PARTICULATES COLLECTED FROM THE AIR. Each sample was collected from the air over a 24-hour period on a weighed 8- X 10-inch flash-fired, glassfiber filter placed on a high volume sampler (U. S. Department of Health, Education and Welfare. 1962). That portion of the sample designated for the determination of metals was then ignited in a furnace at 500 "C. for 1 hour. extracted twice with hot 1-to-1 redistilled nitric acid. filtered. evaporated to 3 or 4 ml., and made up to a final volume of 8.8 ml.. according to a procedure suggested by the Robert H. Taft Engineering Center (U. S. Dept. of Health. Education and Welfare: 1962). A total of 38 samples. collected in Chicago and Cook County. Ill., on March 31, 1966. as well as extracts of unused glassfiber filters were then prepared and made available for analysis by the City of Chicago, Department of Air Pollution Control. To conserve sample, only 4.00 mi. of the original 8.8-ml. sample were used and subsequently diluted 5 to 25 times to
Figure 1. Lead calibration curves
Table I. Standard Deviations of P b Solutions Concn.
H?O background 1 2 5
10 15 18 30 40 50
Av. Absorbance 0.0093 0.0176 0.0362 0.1009 0.1774 0.2888 0.3066 0.3576 0.4668 0.5186
cozficient of variation =
''4 Coeff. St. Dev 0 0 0 0 0
of
No. of
Variationcz Analyses
0020 21 19 0034 0017 4 3 0037 3 0061 2 0 0063 1 0 0056 1 0 0055 1 0 0066 1 0 0087 standard deviation average absorbance
9 9 5 9 6 9 5 8 8 8
5 3 7 7 4 2 8 5 4 7 'O0'
Volume 3, Number 5, May 1969 473
0.15-
I County 3460
j
3ilution
I
*
: n t e r c e p + 1.48
ppr
County 3575 3'l"'ion 1:5 ',tercept 2 . 2 3
PO-
/ i
0 10-
Pb AddNtiori
Figure 2. tions
- ppn
Determination of Pb content by method of addi-
lead concentration of the original solution. Knowing the original weight of particulate sample dissolved in 8.8. ml. of solution and the volume of air that passed through the filter in 24 hours, the quantity of lead per cubic meter of air could then be calculated. The average value of 5 pg. per ml. for the lead content of the glass-fiber filters was obtained by analyzing a solution containing a composite of unused filters. RESULTS OF ANALYSES BY ATOMICABSORPTION. The lead contents of the 38 samples collected from various locations in Chicago and Cook County as determined by atomic absorption varied from a minimum of 0.10 to a maximum of 3.18 pg. of Pb per cu. meter of air (Figure 3). These values fall within the range of 0.1 to 17.0 pg. of lead per cu. meter of air reported by the National Air Sampling Network for urban areas from 1957 to 1963 (U. S. Dept. of Health, Education and Welfare, 1965). The average of 0.82 pg. of lead per cu. meter of air is very close to the mean value of 0.8 found by determining lead contents over 12 different urban areas by arc emission spectrography (U. S. Dept. of Health, Education and Welfare, 1965). In Figure 4A, the absorbance of each unknown solution, prepared from a field sample and containing a lead addition of 0 pg. of lead per ml.. is plotted against the concentration
Lead content of sample = (intercept X dilution factor of solution A X dilution factor of solution B) - p b content of filter (5 p.p.m.)]. Therefore, Lead (County 3460) = (1.48 X 20 X 514) 5 = 32 p.p.m. Lead (County 3575) = (2.23 X 5 X 5/41 - 5 = 8.9 p.p.m.
e
0
o
0
0 00 O
0
0
D
0
C.84
22
LAKE MICHIGAN
o c 0
a 10 0
0 72
2
0
0 63
A
0.27
6
EISENMMR X . W I I
0 85
W!zQ Bclp
COOK COUNTY ILLrrJorS
d
-+7-
0 63 019
,
I
I
\
024
070 052
029 043
Figure 3. Lead concentrations (microgram per cubic meter) samples in Cook County, Ill., on March 31, 1966 Wind conditions were as follows: up to 0800 hours, wind light and variable. From 0800 to 2200, wind direction South and South-westerly, average 18 knots. Increasing cloudiness. Temperature rose abruptly with overcast condition indicating a warm front passage. From 2200 to midnight, wind shifted to Westerl: Sky coyer cleared at 2200
.
474 Environmental Science & Technology
.
A
0
8
10
1
December 5 , 1966
Joouory 17, 1967 Jonuary 24, 1967 0 February 13, 1967 I March 23, 1967 0
I03
0 51
4
of the solution as determined from the method of standard additions. In the absence of a matrix effect, the plot in Figure 4,A should be a straight line similar to a calibration curve for pure lead as shown in Figure 4 3 . However, the point scatter in Figure 4,A greatly exceeds that in Figure 4 3 , which was plotted from data obtained over a period of several months. It was thus concluded that the scatter in Figure 4,A exceeded that which could be expected from the day-by-day variation in instrument performance and was due to the effect on the lead absorption signal of different concentrations of dissolved solids in the 38 field samples-Le., owing to a matrix effect. Polarography, a Referee Method. The technique of polarography was employed to check some of the results obtained by atomic absorption. Since the presence of nitric acid interfered with the analyses, the nitric acid in the original solutions was evaporated, and the solutes were redissolved in hydrochloric acid and adjusted to pH 3 using 50z NaOH to neutralize the larger part of the acid and completing the p H adjustment with dilute NaOH. The volume was finally diluted to 25.00 ml. If the pH was greater than 4, a precipitate appeared. An aliquot of 4.00 ml. of the 25-ml. solution was placed in the electrolysis vessel, 1-ml. of 0.5M NaCl was added as supporting electrolyte and the current-voltage curve was determined using the Sargent Model XXI polarograph under the conditions described in the experimental section. Two more curves were obtained upon two separate additions of 1.00 ml. of a standard lead solution of 20 to 60pg. per ml. The concentration of the solution was then calculated from the diffusion currents obtained from the curves for each determination (Willard. Merritt, et al., 1965b). A comparison of the analyses by polarography and by atomic absorption (before correcting for the lead content of the glass-fiber filters) may be found in Table 11. The results show substantial agreement. Discussion Atomic absorption spectroscopy provides a simple. precise technique for determining the lead content of suspended particulate samples collected from air. Once the sample has been put into solution, no further wet chemical methods, other than dilution, are required. However, the possibility of a matrix affecting the absorption of lead, as suggested from results in Figure 4. necessitates employment of the method of standard additions (Willard, Merritt. et al.. 1965a). The data presented here were determined over a period of four months. This represents a relatively long-term study involving many samples and is more likely to bring out longterm instrument and matrix effects than shorter-term studies. Also. this longer term study approaches the conditions met by an instrument routinely operated under field conditions Since the lead concentrations are in the range of 0 to 100 pg. of Pb per ml. and the two analytical techniques are so drastically different, the agreement obtained between atomic absorption and polarography is considered satisfactory (Table 11). Having established the range of lead concentrations in the samples. it will be possible in the future to carry out the analyses using only 1.00 ml. of the original sample, diluted to a total of 20.00 ml. Recently, an improved lead hollow cathode lamp employing the molten metal principle (Vollmer, 1966) has become available. This lamp should increase the precision of lead analyses so that future determinations might be performed with even smaller sample volumes. Application of the atomic absorption technique to the analyses of other metals in suspended particulates, such as vanadium, is currently being investigated.
Table 11. Lead Content Obtained by Atomic Absorption and Polarography Pb Content of S o h . pG./MI. by At.
Sample
Absorption. Polarographya
No.
A.A.
Pol.
Filter Extract County 3595 Chicago9642 Chicago 9702
5.0 47.1 63.9 75.8
4.8 43.2 62.4 73.1
a
*
Sensitivity, Differenceb pA./Mm. 4.0 0.004, 0.003 8.3 0.010 2.3 0.010, 0.006 3.6 0.010
= atomic absorption data. Pol. = polarography data. at. absorption value-polarography value difference = x 100. at. absorption value
A.A.
Although the lead contents were below the threshold limit value of 0.2 mg. per cu. meter of air (adopted at the 22nd Annual Meeting of the American Conference of Governmental Industrial Hygienists in April 1960). the highest values were found in samples taken from stations nearest the expressways and in the more industrial areas. The dry ashing procedure previously described resulted in losses of 11 to 337, of the lead collected on the filters (Burnham, Moore. et a/., 1968). Thus, the values reported here in micrograms of lead per cubic meter of air should be t-cik en as the minimum amounts of lead in the air on March 31, 1966. Conclusions Lead concentrations in samples containing complex matrices may be efficiently and precisely determined by applying the method of standard additions to atomic absorption spectroscopy. Thus, many of the tedious wet chemical procedures and interferences inherent in some of the more familiar techniques such as the dithizone method (Snyder, 1947) may be avoided. Literature Cited Boling, E. A,, Spectrochim. Acta 22, 425-31 (1966). Burnham, C. D., Moore, C. E., Kanabrocki, E., Hattori, D. M., Loyola University, Chicago, Ill.. unpublished data, (1968). Chakrabarti, C. L., Robinson, J. W., West, P. W., Anal. Chim, Acta 34,269-77 (1966). Dagnall, R. M., West, T. S., Talanta 11, 1553-7 (1964). Keenan, R. C., Holtz, J. L., Am. Ind. Hyg. Assoc. J . 25, 254-63 (1964). Perkin-Elmer Corp., Norwalk, Conn., “Analytical Methods for Atomic Absorption Spectrophotometry,” October 1966. Snyder, L. J., Anal. Chern. 19, 684-7 (1947). U. S. Dept. of Health, Education, and Welfare, Public Health Service, Washington, D . C.. “Air Pollution Measurements of the National Air Sampling Network 1957--1961,” Publ. 978. 1962. U. S. Dept.’of Health, Education, and Welfare, Public Health Service, Washington, D. C., “Air Pollution Measurements of the National Air Sampling Network 1963,” 1965. Vollmer, J., Atomic Absorption Newsletter 5, 35, (1966). Willard, H. H., Merritt, L. L., Jr., Dean. J. A., “Instrumental Methods of Analysis,” pp. 342-3, Van Nostrand, Princeton, N. J., 1965a. Willard, H. H., Merritt, L. L., Jr., Dean, J. A.. “Instrumental Methods of Analysis,” p. 693, Van Nostrand, Princeton, N. J., 1965b. Received for review December 19, 1967. Accepted February 16, 1969. This work was supported in part by a grant from the Dicision of Air Pollution, Bureau of State Sercices, Public Health Sercice, AP 00444-02. Volume 3, Number 5, May 1969 475
