Environ. Sci. Technol. 1084, 18, 818-822
X-ray Analysis of Airborne Particulates Collected by an Andersen Sampler. Compound and Elemental Distributions vs. Particle Size of Laboratory Particulates Masaakl Iwatsukl, SuJlth P. Tlllekeratne, Tsuglo Fukasawa, and Tsutomu Fukasawa,
Department of Applied Chemistry, Faculty of Engineering, Yamanashi University, Takeda-4, Kofu-shi 400, Japan Polycarbonate films (80-mm diameter) of 15 mg were prepared on the standard glass plates of an Andersen cascade impactor air sampler and used as collection substrate. After sampling, the particulate-loaded film was re-formed into a 16-mm diameter film with a few drops of dichloromethane. Distribution curves of compounds or elements vs. particle size were constructed by using the strongest diffraction line intensities of compounds or Ka line intensities of elements after X-ray diffraction or fluorescence analyses of the identical samples. Good recoveries of some elements in the preparation of a small-fii sample were ascertained by neutron activation analysis. Adequate reproducibility of the small-film sample was confirmed by X-ray diffraction and fluorescence analyses. This method provides about 25-fold improvement in sensitivity and permits X-ray diffraction and fluorescence analyses of both soluble and insoluble constituents in particulates collected by an Andersen sampler. An application to laboratory particulates and discussion are also given.
Introduction Many papers and reports have been published on the distribution curves of element concentration vs. particle size for airborne particulates by using the Andersen cascade impactor sampler and various analytical methods as described in our previous paper (I). No paper, however, has been published so far on the X-ray diffraction (XRD) analysis of the particulates fractionated by the Anderson sampler except for our previous paper (I). In the previous paper (I), airborne particulates were collected on Nuclepore filters (80-mm diameter) by an Andersen sampler, and then each of the filters loaded with particulates was re-formed into a small 16-mm diameter film after dissolution in dichloromethane, centrifugation, and pipetting the supernatant. This permitted the XRD analysis and construction of the distribution curves of compound concentration vs. aerodynamic particle size, which provided valuable information in studies of environmental problems. However, in addition to using expensive Nuclepore filters, the method is not applicable to the determination of constituents that are soluble in the solvent. In the present paper, we carried out a study to develop a method, which does not use the membrane filters and is applicable to both XRD and X-ray fluorescence (XRF) analyses of airborne particulates containing constituents soluble in the solvent. This paper describes the preparation of large thin polycarbonate film (80-mm diameter) as the collection substrate, re-formation of the large film loaded with airborne particulates into a small flat film of 16-mm diameter, recovery of particulates in the re-formation, and reproducibility of XRD and XRF intensities from the small-film sample: The recovery was estimated by neutron activation analyses of some elements of soluble forms. This method provides about 25-fold sensitivities in both XRD and XRF analyses of airborne particulates collected by an Anderaen sampler and enables construction of the compound and elemental curves for identical air818
Environ. Sci. Technol., Vol. 18, No. 11, 1984
Table I. Conditions of XRD Analysis X-ray tube voltage, kV current, mA filter d and s slit, deg
Cu 35 14 Ni 1
r slit, mm time constant, s scan speed, degfmin chart speed, mmfmin sample spin
0.6 4
5 on
borne particulates. The method was used to construct distribution curves of compound and element concentrations vs. particle size for particulates collected in a room of an analytical chemistry laboratory.
Experimental Section Polycarbonate Solution, Backup Filter, and Homogenized Airborne Particulates. Polycarbonate solutions of 10 and 3 mg/mL were prepared by dissolving Panlite powder (Teijin Co. Ltd.) in analytical-grade dichloromethane. Fuji FM-80 microfilter (pore size 0.8 km; acetylcellulose; Fuji Photo Film Co. Ltd.) of 80-mm diameter and 210-mg mass was used as the backup filter for the collection of submicron particles. A homogenized airborne particulate sample denoted by AS-5 (2) was prepared by using particulates collected on a filter attached to the inlet of an air cleaner on the roof of a tall building in a business district of Tokyo in Jan 1975. Apparatus. Airborne particulates were collected by an Andersen cascade impactor sampler, Koritsu Model KA 200, consisting of eight stages with removable glass plates (80-mm diameter) as the standard collection media. A constanbhumidity box (type C-3, Doi Co. Ltd., made of acrylic resin) was used to control the sample moisture. Humidity in the box was kept at 50% with 43% sulfuric acid. A Sartorius semimicrobalancewas used for determining the tare weight of freshly prepared large films on the glass plates and for film after collection of particulates. A Cahn 26 automatic ultramicroelectrobalance was used for weighing the other samples. A Sakuma centrifuge was used at 2000 rpm (500g) for centrifugation of particles. A Rigaku X-ray diffractometer equipped with a rotating sample holder was used for the XRD analysis. The small-film sample was stuck onto a nondiffracting singlecrystal quartz plate by using a drop of dichloromethane and mounted on the rotating sample holder. The sample was rotated during intensity measurements to reduce errors caused by nonuniform deposition of crystallites. After XRD analysis, the film can be stripped off for other uses. Operating conditions are shown in Table I. A Philips PW 1410 semiautomatic X-ray spectrometer was used for the elemental analysis. The film sample was placed between two nylon nets set in a standard aluminum holder for heavy elements and between a nylon net and a tungsten mask (aperture 10-mm diameter) set in the holder for light elements. Operating conditions are shown in Table 11.
0013-936X/84/0918-0818$01.50/0
0 1984 American Chemical Society
Table 11. Conditione of XRF Analysis heavy elements X-ray tube voltage, kV current, mA collimator detector analyzing cryst scan speed, deg/min chart speed, mm/min spinner path
light elements
W
Cr
45 30 fine fc and sc
40 34 coarse fc
LiF
EDDT
1 5
5
on vacuum
on vacuum
1
All intensity measurements in the XRD and XRF analyses were carried out by chart recording. Neutron activation analyses were carried out by using the reactor JRR-2 and a y-ray spectrometer equipped with a Ge(Li) detector in National Universities' Laboratory for the Common Use of JAERI Facilities (Tokai). Recommended Procedures. (1) Preparation of 80mm Diameter Film, Collection of Particulates, and Weight Distribution Curve. Five-milliliter polycarbonate solutions (3 mg/mL) are pipetted separately onto eight clean glass plates (80-mm diameter) of the standard collection media, and the solvent is evaporated to make thin films of 80-mm diameter on the glass plates. These plates and a backup Fuji microfilter are kept in the 50% humidity box for at least 1 day to control moisture (3),weighed, and arranged in order in the Andersen sampler, After sample collection, the plates and the Fuji microfilter with particulates are placed in the humidity box and weighed. The distribution curve of weight vs. particle size is constructed by using the Lagrange interpolation equation with the aid of a computer as described in previous papers (1,4). (2) Preparation of 16-mm Diameter Flat Film with Embedded Particulates for X-ray Analysis. After being weighed, each particle-loaded polycarbonate film (80-mm diameter) is stripped off from the glass plate by using a pair of tweezers and placed onto an 80-mm diameter watch glass which has a 16-mm diameter circle marked on its backside. A round homogeneous film of 16-mm diameter with embedded particles is made with the aid of a few drops of dichloromethane and a thin glass rod. The polycarbonate f i i blank for the XRF analysis is prepared with 15 mg of polycarbonate powder and a few drops of dichloromethane. The Fuji microfilter loaded with the submicron particles is centrifuged with 10 mL of dichloromethane for 30 min at 2000 rpm in a 15-mL centrifuge tube with a cork stopper. Nine milliliters of supernatant is pipetted and discarded for reduction of the filter material, and the remainder is evaporated to form an irregular film on the bottom of the tube. This film is transferred onto a watch glass by using a pair of tweezers and re-formed into a film of 16-mm diameter. Similarly the blank for XRF analysis is also prepared. These films both with and without embedded particles are pressed between two flat tungsten-carbide blocks under 6 X lo3 kg/cm2 and at 50 "C during 10 min to get improved surface for the X-ray analysis. (3) Identification of Compounds and Construction of Distribution Curves of Compounds and Elements vs. Particle Size. The identification of compounds are carried out by using the JCPDS cards and/or others aided by results of the XRF analysis. Use of the strongest diffraction line of each compound is generally recommended for the construction of the distribution curve of compound
concentration vs. aerodynamic particle size. The distribution curve of element concentration vs. particle size is constructed by using the Ka!line intensity of the element found by the XRF analysis of the film sample identical with the sample used for the XRD analysis. The compound and element distribution curves are constructed as described in the previous paper (1). They are compared to each other for reconfirmation of the identification. Recovery Test of the Particulates in Preparation of Small-Film Sample. Recoveries of some elements were investigated by neutron activation analysis for information about the recovery of the particulates in the preparation of small films. Three-milliliter polycarbonate solutions (10 mg/mL) were pipetted separately onto eight clean glass plates (Wmm diameter), and 80-mm diameter films were formed on them after solvent evaporation. Airborne particulates were collected on these films by the Andenen sampler, and the films were stripped off and cut into equal halves. A half from each stage was transferred onto a watch glass and formed into a 16-mm diameter film (A) and subjected to neutron activation analysis together with the remaining untreated half (B). Estimation of the recovery was also carried out with AS-5 as follows. A blank polycarbonate film (30 mg) of 80-mm diameter was divided into equal halves, onto which AS-5 of 5 mg each was added. A 16-mm diameter film (A) embedded with the particulates was prepared from one half and subjected to neutron activation analysis together with the remaining untreated half (B). Recovery was estimated by comparison of the y-ray intensities of the same radionuclide on both (A) and (B), after half-life correction. Recovery in the centrifugation-concentrationtechnique of the previous paper (1)was also studied to show clearly the capability of the new method for determination of soluble constituents. Airborne particulates were collected on Nuclepore filters (80-mm diameter) by the Andersen sampler. Each particulate-loaded filter was cut into equal halves, one of which was centrifuged in 5 mL of dichloromethane in a 15-mL centrifuge tube for 30 min at 2000 rpm: Five milliliters of the solvent was used for the experiment under the same concentration on the filter material and particulates. The 4.5-mL supernatant was pipetted and discarded, and the remainder containing particles was evaporated to form an irregular film on the bottom. This film was re-formed into a 16-mm diameter film (A) on a watch glass with a few drops of dichloromethane and a thin glass rod. Neutron activation analysis of film (A) and untreated half (B) was carried out. Recovery was estimated as described. In addition, 5 mg of AS-5 was also centrifuged together with a Nuclepore filter (80-mm diameter) in 10 mL of dichloromethane. The 9-mL supernatant was pipetted onto a watch glass and evaporated to form a relatively large film, from which another 16-mm diameter film (C) was prepared. The remainder (1mL with the particulates) was evaporated, and the resulting irregular film was stripped off and re-formed into a 16-mm diameter film (D). These two films were subjected to neutron activation analysis. The recovery was estimated as D / ( C D). ReproducibilityTest of XRD and XRF Intensities. Polycarbonate f i i of about 20-mm diameter was prepared with 15 mg of polycarbonate and a few drops of dichloromethane. The homogeneous particulate A S 4 (5 mg) was weighed precisely on this film with the ultramicrobalance, and a round homogeneous film of 16-mm diameter with embedded particles was prepared on a watch glass
+
Envlron. Scl. Technol., Vol. 18, No. 11, 1984
819
Table 111. Recovery of Elements in Preparation of Small-Film Sample by the New Method element
sample
Mn
stage 4 stage 7 stage 3 stage 2 stage 6 stage 8 AS-5 ( 5 mg) and film
A1 Na Mn
recovery, %
::1
Table IV. Recovery of Elements in Preparation of Small-Film Sample by Centrifugation-Concentration Technique element Mn
1 av 100
90 86 87}av 93 106 100
Al Na Mn
as described. Four other equivalent samples were prepared similarly. These films were pressed to get improved flatness, followed by the XRD analysis. The homogeneous particulate sample used herein contained gypsum, aquartz, and plagioclase as the main compounds (2). Intensities of their selected planes were measured. Subsequently these films were subjected to XRF analysis.
Results and Discussion Preparation of Large-Film and Small-Film Samples. In the previous paper (I), a Nuclepore filter (80-mm diameter) loaded with the particulates, consisting of 50 mg of polycarbonate, was reduced to one-tenth of its original polycarbonate mass by the centrifugation-pipetting procedure after dissolution in dichloromethane. Then the 16-mm diameter film with the concentrated and embedded particles was prepared from the remainder for the XRD analysis. We also tried the preparation of an 80-mm diameter film using a solution containing 5 mg of polycarbonate. This film, however, was too thin to be stripped off easily from the glass plate by tweezers without loss of particulates. Actually film prepared with larger quantities of polycarbonate (30-50 mg) was easy to remove from the glass plate but led to higher background intensities in both XRD and XRF analyses. Finally, we found that the use of 15 mg of polycarbonate was suitable for making an easily removed film and produced low background intensities in the X-ray analyses. A small film (16-mm diameter) prepared by using 5 mg of polycarbonatewas thin and gave complete flatness when mounted on the quartz plate with a drop of dichloromethane for XRD analysis. However, the 16-mm diameter film formed from 15 mg of polycarbonate was rough and did not gain complete flatness when mounted on the quartz plate with the solvent. Therefore, the film was pressed between two flat tungsten-carbide blocks. I t is obvious that extremely higher pressures and temperatures would produce undesirable effects on the shape and properties of the crystalline compounds in samples, and lower temperature and pressure may not give adequate flatness. Our study indicated that pressing under 6 X lo3kg/cm2 at 50 OC gave adequate flatness of the film sample for the XRD analysis. The pressing under these conditions had no significant effect on XRD patterns of thin film samples of some airborne particulates studied. Recovery of the Particulates in Preparation of Small-FilmSample. Recoveries of three or four elements are compared in the preparation of the small-film sample and shown in Table I11 for the new method and in Table IV for the centrifugation-concentrationtechnique. Table I11 shows that the average recoveries of these elements by the new method were 90-100%. Considering the expected precision of neutron activation analysis and the heterogeneity of the particulates, we believe that preparation of small-film samples was successful without significant loss of the particulates. On the other hand, Table IV shows that the average recoveries using the centrifugation technique of four elements were 64-74% for the particulates 820
Environ. Scl. Technol., Vol. 18, No. 11, 1984
sample
recovery, %
stage4 stage 7
1
6o av 64 68 /av 6 5
:?
stage stage 43 stage 6 stage 8 AS15 ( 5 mg) and filter
~~
1av 74
95
~~
Table V. Reproducibility of XRD Intensitiesa
--- &-quartz
linemeasured av, x10 cps on..,, % a
gypsum
plagioclase
1 0 1 100 1 2 1 1 4 1 002 002 040
24.7 5.2
8.4 6.3
5.2 7.1
4.7 8.3
7.1 7.6
For 5 mg of AS-5.
Table VI. Reproducibility of XRF Intensitiesn
av, X10 cps gn-1,
%
Fe
Zn
element Mn Cr
1692
80 3.8
30 3.1
1.9
7.9
6.8
Ni
Pb
7.4 11.5
5.6 4.0
=For 5 mg of AS-5.
collected by the Andersen sampler, and significantly low, though the recovery of manganese in AS-5 containing larger particulates seemed to be good. Our results show that airborne particulates contain significant amounts of the elements in solvent-soluble forms, and therefore the centrifugation-concentration technique gave rise to significant loss of the soluble elements. We believe that the new concentration technique, which also gives good recovery for the elements in soluble forms, can be successfully applied to the XRF analysis of particulates samples, even if they contain substances soluble in dichloromethane. In dissolution of the film, some particles may be dissolved and solidified after solvent evaporation. Newly crystallized and recrystallized substances, however, may allow to be determined by XRD analysis. On inorganic particles found herein as well as in our previous paper ( l ) no , effect was found on XRD analysis. Reproducibility of XRD and XRF Intensities. Table V shows intensities and their relative standard deviations obtained in the XRD analysis of a-quartz, gypsum, and plagioclase in five 16-mm diameter film samples prepared. Table VI shows XRF intensities of some elements and their relative standard deviations for the identical samples in the order of their intensities. Relative standard deviations for the major diffraction lines of each compound were 5.2-8.3%. On the other hand, the relative standard deviations in the XRF analyses were 1.9-4.0% except 6.8% of Cr Ka and 11.5% of Ni Ka! which may be due to their low intensities and/or some heterogeneity. Results of the XRF analysis indicate that the small-film samples prepared have good reproducibility with a relative standard deviation of 5 4 % in the XRD analyses. Application to Laboratory Particulates. Particle collection was carried out during Nov 25-Dec 13,1981 (dry season), and during June 19-29, 1981 (wet season), in a room of the analytical chemistry laboratory at a constant flow rate of 28.3 L/min. (1) Concentration of Particulates. The total mass of collected particles during winter and summer were 33.0
I \j: \
\
t L
t
I 5
hY = 3
h I-
g1 2 Y s v-
0,5
1
2
5 7 10
3
D (rm)
Flgure 3. Distribution curves of compound concentration vs. particle size for laboratory particulates in winter (1981). For symbols see Figure 2.
1
I
n
2
1
0.5
D
3
5
7
1
0
(rem)
F W e 1. Distributioncurves of welght vs. partlcie size. (A) Laboratory particulates in winter (1981); (8) laboratory particulates In summer (1981); (C) outdoor particulates In winter (1982).
- 60
Y
50 0 Y
-$
40
5
20
--\
A
0.5
10
2
1
3
5
7
1
0
(vm) Figure 4. Distribution curves of elemental concentrationvs. particle size for S, Ci, Ca, and Si in laboratory particulates (winter). D
OLI
;5
30
35 40 20' for Cu KO
45
50
Flgure 2. Examples of XRD patterns of smali-film sample (16-mm diameter) embedded with airborne particulates. (a) For stage 4, 1.6 mg of particulates; (b) for stage 8, 6.9 mg of particulates. Collected In winter (1981); full scale 8 X IO' cps. Q, a-quartz; P, plagioclase; C, calcite; NS, (NH,),(NO,),SO,; S, (NH4),SO4; CI, NH,CI.
(46 pg/m3) and 16.0 mg (39 pg/m3), respectively. Concentrations of the airborne particulates inside the laboratory were almost the same in both dry winter and wet summer, which were also similar to the concentration (37 pg/m3) of the outdoor particulates collected during rainy days in summer (July 2-13,1982) and significantly lower than those of the outdoor in dry winter, e.g., 68 pg/m3 (Jan 12-23, 1982)) in the same place (1). (2) Distribution Curve of Weight vs. Particle Size. Figure 1shows particle size distributions for the particulates collected in winter (A) and summer (B)inside the laboratory together with an example (C)of the outdoor particulates in the dry winter. There was a similarity between curves A and B, where larger distributions appeared toward the fine particle region with a small peak in the 3-7-pm region. It differed from the curve of the outdoor particulates with a significantly large peak in the 3-7-pm region. The difference between the laboratory and outdoor particulates may be attributed to the removal of larger particulates from the atmosphere when air was introduced into the room.
(3) X-Ray Diffraction Patterns and Identification of Compounds. Figure 2 shows examples of the diffraction patterns observed on small-film samples embedded with the winter particulates, where sharp peaks were visible though there were high backgrounds with decreasing diffraction angle. This indicates the effect of concentration of the spotty dispersed particulates into a small-film sample. Improvement in sensitivity is about 25-fold. The difference between the backgrounds of XRD patterns for stage 4 (a) and stage 8 (b) was caused by the difference in the amount of embedded particulates, i.e., 1.6 and 6.9 mg, respectively. Ammonium chloride, ammonium sulfate, ammonium nitrate sulfate, a-quartz, and plagioclase were identified as the major crystalline species together with trace calcite in the laboratory particulates. (4) Distribution of Compounds and Elements vs. Particle Size. Figure 3 shows distribution curves of compound concentration vs. particle size €or laboratory particulates collected in winter (1981). It indicates that most of the ammonium-containing compounds were accumulated in the fine particle region, whereas a-quartz and plagioclase were in the coarse particle region. Figures 4-6 show the distribution curves of elements vs. the particle size for the identical sample. The distribution curves of S and C1 resembled those of their compounds, i.e., amEnvlron. Sci. Technoi., Voi. 18, No. 11, 1984 821
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I
1 \
0
1
0.5
2
5
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1
.
,
\
',.>
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.
,
0
D (urn) Figure 5. Distribution curves of elemental concentrationvs. particle size for K, Ti, and Fe in laboratory particuiatgs (winter).
I
I
1
2
I
3 D (urn)
I
I
' I
5 7 1 0
Flgure 8. Distribution curves of elemental concentrationvs. particle size for Mn, Zn, and Pb in laboratory particulates (winter).
monium sulfate, ammonium nitrate sulfate, and ammonium chloride, respectively. It shows that the main parts of sulfur and chlorine were contained in the forms of ammonium sulfates and ammonium chloride, respectively. Ammonium-containing compounds were found in large concentration, because of the high usage of ammonium compounds in the laboratory. Distributions of Si and Ca resembled those of their related compounds such as aquartz and plagioclase. I t shows that the principal contributions of silicon and calcium in these laboratory particulates were contained in the forms of quartz, plagioclase,
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Environ. Scl. Technol., Vol. 18, No. 11, 1984
1981, 30, T55-T60. (4) Fukasawa, T.; Iwatsuki, M.; Ito, J.; Hayashi, E.; Kamiyanagi, T. Nippon Kagaku Kaishi 1982, 1940-1945.
Received for review July 18,1983. Revised manuscript received January 6,1984. Accepted May 2,1984. The work reported here has been supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Japan.
