Emission Spectrographic Determination of Trace Elements in Airborne Particulate Matter Akiyoshi Sugimae
Environmental Pollution Control Center, Osaka Pref., I-chome, Nakamichi, Higashinari-ku, Osaka, Japan
An emission spectrographic method has been used extensively for the determination of trace elements in airborne particulate matter, especially in a large-scale survey work, for which the potentiality for simultaneous multielement analysis is an important advantage (1-13). Airborne particulate matter is routinely collected by aspirating a measured volume of air through a glass fiber filter ( 2 2 , 24). However, for the determination of trace elements in airborne particulate matter, the chemical composition of the filter is important. The filter should be free of any elements presumably present in the airborne particulate matter itself. The glass fiber is definitely not suitable for the analysis for Ba, Sr, Rb, Zn, Ni, Fe, Ca, As, and so forth because of the high content of these elements in the glass fiber filter (10, 15, 16). In recent years, a membrane filter has played an increasing role for the collection of airborne particulate matter because of the low content of impurity elements. However, the application of the emission spectrographic method for the analysis of the airborne particulate matter collected on the membrane filter has been limited. Brash (1) has described a procedure for the determination of beryllium in airborne particulate matter on a membrane filter. The membrane filter was treated with concentrated nitric acid and perchloric acid after being charred with concentrated sulfuric acid. The clear solution obtained was analyzed by a solution-spark technique using a rotating disk electrode. However, the sample preparation is fairly complicated, and the sample thus prepared is highly diluted, with an adverse effect on sensitivity and the increased possibility of contamination. A powder-arc technique is preferable for the determination of trace elements. However, a dry ashing of the membrane filter is difficult because the filter flashes when ignited. Imai et al. ( 3 ) have described a powder-ac arc technique in which the membrane filter was moistened with ethyl alcohol and burned slowly, the carbonized ash was ignited about 2 hours by a plasma asher, the decolored ash was Brash. Appl. Spectrosc.. 14, 43 (1960). Hochheiser, F. J. Burman, and G . B. Morgan, Environ. Sci. Techno/.,5 , 679 (1971). (3) S. Imai. K . ito, A. Hamaguchi. Y . Kusaka, and M . Warashina, Jap.
(1) M . P. (2) S. S.
Anal. 22, 551 (1973). (4) T. Hasegawa and A. Sugimae. Jap. Anal., 20,840 (1971) (5) T. Hasegawaand A. Sugimae. Jap. Anal.. 20, 1406 (1971). (6) D. W. Lander, R. L. Steiner, D. H . Anderson, and R. L. Dehn. Appl. Spectrosc.. 25, 270 (1970). ( 7 ) N . L. Morrow and R. S. Brief. Environ. Sci. Techno/.. 5, 786 (1971). (8) R. L. O'Neii, Anal. Chem., 34, 781 (1962). (9) A . Sugimae and T. Hasegawa, Jap. Anal.. 22,3 (1973). (10) A . Sugimae, Intern. J. Environ. Anal. Chem., in press. (11 ) U.S. Dept. Health. Education. and Welfare, Public Health Service, Washington, D.C., "Air Pollution Measurements of the National Air Sampling Network," (1962). (12) P. W . West. "Chemical Analysis of Inorganic Pollutants." in "Air Pollution." Voi. ( I , A . C. Stern, Ed.. Academic Press, New York. N . Y . , 1968 (13) B. V . Wheeler, W . A . Ryder, and K . R. Arnold. Appl. Spectrosc.. 16, 17 (1962). (14) FederalRegister. 36, 8191 (1971). (15) T. J. Kneip. M . Eisenbud. C. D. Strehlow. and P. C. Freudenthal, J , AirPollut. Contr. Ass.. 20, 144 (1970) (16) J. Leroux and M . Mahmud, J. Air Pollut. Contr. A S S . . 20, 402 (1970).
mixed with lithium carbonate-graphite buffer, and ac arc excitation was used for the quantitative determination of 13 elements in airborne particulate matter. However, there is a considerable risk that loss of volatile elements could occur during the burning of the filter. This paper describes a powder-dc arc technique for the determination of trace elements in the airborne particulate matter collected on a membrane filter. The membrane filter on which airborne particulate matter is collected is dissolved in acetone, and the airborne particulate matter is separated from the filter. After centrifuging, the powder obtained is washed three times with acetone, dried, and mixed with sodium fluoride and graphite powder. The resulting mixture is packed in a graphite cup electrode and excited by a dc arc.
EXPERIMENTAL Sample Preparation. Air was drawn through a membrane filter (Gelman DM-800, 47 mm in diameter, pore size: 0.8 pm) a t a flow rate of 30 l./min for 7 days and airborne particulate matter was collected on the filter. Before and after collection of airborne particulate matter, the filter was weighed. The weight of the particulate matter on the filter was computed. Atmospheric concentration of airborne particulate matter could be calculated by dividing the weight by the air volume sampled. The filter was placed in a 10-ml tared centrifuge tube and 10 ml of A.G. grade acetone was added to the filter. The filter was dissolved in the acetone. The airborne particulate matter was separated from the filter and suspended in the acetone. The particulate matter was centrifuged a t a rotating speed of 2000 rpm for 20 minutes. The acetone was run off and discarded. The particulate matter was washed with 10 ml of acetone and centrifuged for 10 minutes. This procedure of washing was repeated three times to remove all the residue of the membrane filter from the particulate matter. The particulate matter was then dried a t 110 "C for 1 hour and cooled in a desiccator. The particulate matter was weighed t o determine the percentage of acetone soluble materials in the airborne particulate matter and crushed with an agate mortar and pestle. The 1-part particulate matter and 2part spectroscopic buffer were weighed into a polystyrene vial containing a 3&in. Plexiglas ball and shaken in a Spex Industries So. 3140 mixer-mill. The spectroscopic buffer is composed of 1part sodium fluoride and 1-part graphite powder (National Carbon SP-2), and contains 100 ppm indium oxide and 20,000 ppm tantalum oxide. Standards. A base mixture was prepared from Johnson Matthey Specpure chemicals. Oxides of the elements were used except calcium, sodium and potassium, where carbonates were chosen on the grounds of purity. They were thoroughly mixed and sintered a t 1000 "C for 12 hours. After cooling, the sinter was ground in an agate mortar. Carbon powder (National Carbon SP-3) was added to the sinter to give a product of approximately 30% SiOz, 10% Fez03, 3% CaO, 1% MgO, 1.5% NazO, 0.5% KzO, and 48% C. Standards were prepared by adding the desired amounts of Specpure oxides of analytical elements to the base mixture. The standards were then mixed with the spectroscopic buffer. Procedure. The samples and standards prepared for arcing were placed in undercut electrodes. Each electrode was then tapped gently to settle the powder. The charge in the electrode is about 35 mg and, a t that time, the crater of the electrode is filled two thirds full with the powder. The electrode was heated in an electric furnace at 360 "C for 1 hour to prevent any of the powder from popping out of the electrode on ignition. The electrode was then discharged under the conditions summarized in Table I. A A N A L Y T I C A L C H E M I S T R Y , VOL. 4 6 ,
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Table I. Experimental A p p a r a t u s and Conditions
Source unit
Shimadzu 1.7-m plane grating spectrograph (Type GE-170) 1200 lines/mm blazed for 3000 A, 1st order Shimadzu Modularsource (Type
Discharge Sample electrode
280000) 15-A dc arc Hitachi NE-1205 (ASTM 5-12)
Spectrograph Grating
Counter electrode Analytical gap Preburn time Exposure time Excitation chamber Gas composition Gas flow rate Electrode-chamber base distance Slit width Filter
(cathode) Hitachi CTE-2001, 0.18-inch diameter, pointed. 3 mm held constant None 60 sec Shimadzu Stallwood jet 10% oxygen, 90% argon 10 l./min 6 mm 10 r m 3-step filter (Transmission: 4,20,100%) 4- X l0:inch Kodak SA-1 plates, processed with D-19 developer for 4 min at 2OoC, stopped in running water, fixed for 3 min,
Film
Comparator
rinsed in water, and air-dried Nippon-Jarrell-Ash microphotometer (Type JM-3)
Table 11. Analytical Line Pairs and Working Ranges
Be Bi Cd Cr Cu Mn Ni Pb Sn Ti V Zn
I1 3130.416 I I I I I I I
I I I I
4 /Ta I 3012.537 rib
3067.716 Ab/In I 3039.356 3261.057 A /In I 3039.356 3021.558 A /Ta I 3012.537 3275.962 Aa/TaI 3012.537 3044.567 h; /Ta I 3012.537 3050.819 /Ta I 3012.537 2833 .OS9 AU/In I 3039.356 3262.328 Rb/In I 3039.356 2956.131 Ab/Ta I 3012.537 3183.952 A /Ta I 3012.537 3282,333 Ab/In I 3039.356
Aa
Ab Ab
Ab Ab An
.kb Ab k
Range, rg/g
1-100 2-200 2-200 10-1000 20-2000 50-5000 10-1000 50-5000 10-1000 20-2000 10-1000 50-5000
a Spectrum at 4% tranamittance part of step filter. b Spectrum at 20% transmittance part of step filter.
list of analytical line pairs used and working ranges is given in Table 11.
RESULTS AND DISCUSSION Morrow and Brief ( 7 ) have reported that the concentration of silicon, aluminum, calcium, and magnesium in the atmosphere correlated with each other and that the relative proportions of these elements agreed surprisingly well with the relative proportions of these elements in the lithosphere. However, the concentration of sodium which occurred as ocean-generated NaCl aerosol, varied independently to the other elements. The author et al. (17) have reported that the iron content in airborne particulate matter collected a t commercial and residential areas, agreed with that in the lithosphere. From these results, it might be thought that the content of the major constituents, except sodium, in airborne particulate matter varied to a small extent. Moreover, it was anticipated that elements other than silicon, iron, aluminum, calcium, magnesium, sodium, and potassium would be present in ex(17) A . Sugimae. Y . Matsuo, and T. Hasegawa, J. Jap. SOC.Air Pollut. in Dress.
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Table 111. Comparison of Emission Spectrographic and Atomic Absorption Analysis, gg/g Emission spectrographic Element
A
Be Bi Cd Cr cu Mn Ni Pb Sn Ti V Zn
