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Thus, from a qualitative standpoint it is possible to determine the matrix, minor, and trace elements present, to infer the chemical forms in which several of these elemenb are present, and to establish those elemenb which exhibit the phenomenon of surface enrichment. Quantitatively the excellent agreement between the results obtained by SIMS and XRF for bulk analyses provides evidence for the effectivenessof the MISR correction procedure in this sample. Consequently, it is reasonable to suppose that the surface analytical data presented in Table I together with the surface enrichment factors and depth profiles in Table I1 and Figures 5-7, respectively, constitute quantitative measurements. In order to achieve such quantitative measurements, however, it is necessary to render the sample electrically conductive, to limit the analytical region precisely, and to apply a matrix correction which changes sequentially with depth as the composition changes. It should be noted that single particle analyses were not performed in the present SIMS study. Such analyses are, however, possible using more modern ion microprobes which also provide improved quantitation capabilities in terms of sample positioning and sensitivity.
ACKNOWLEDGMENT The authors thank P. Van Dyck (U.I.A.) for performing the
XRF measurements. LITERATURE CITED (1) Leroy, V. Mater. Scl. Eng. 1980, 42,289-307. (2) Lovering, J. NBS Spec. Publ. 1075, No. 247, 135-140.
(3) Proceedings of the 2nd Congress on secondary ion mass spectrometry, Stanford, CA, 26-30 Aug 1979, Springer Series (Berlin). (4) Galle, P. Ann. Phys. Elol. Med. 1070, 1 , 83-88. (5) Llnton, R. W.; Natusch, D. F. S.; Evans, C. A,, Jr.; Willlams, P. Science 1076, 191 852-854. (6) Linton, R. W.; Williams, P.; Evans, C. A,, Jr.; Natusch. D. F. S. Anal. Chem. 1077, 49,1514-1521. (7) Keyser, T. R.; Natusch, D. F. S.;Evans, C. A., Jr.; Linton, R. W. Environ. SC/. Technol. 1978, 12,768-773. (6) Morrison, G. H.; Slodzian, G. Anal. Chem. 1975, 47, 932A-943A. (9) Van Espen, P.; Van Craen, M.; Saelens, R. J . Microsc. Spectrosc. Electron. 1081, 6 , 195-199. (io) Van Craen, M.; Van Espen, P.; Adams, F. Rev. Sci. Insfrum., in press. (11) Dewolfs, R.; Deneve, R.; Adams, F. Anal. Chim. Acta 1975, 75, 47-60. (12) Van Dyck, P.; Markowicz, A.; Van Grieken, R. X-Ray Spectrom. 1980, 9 , 70-78. (13) Plog, C.; Wiedmann, L.; Benninghoven, A. Surf. Sci. 1977, 67,565. (14) Van Craen, M.; Denoyer, E.; Adams, F.; Natusch, D. F. S., submltted for publication in Environ. Sci. Technol. (15) Ganjei, J. D.; Leta, D. P.; Morrison, G. H. Anal. Chem. 1978, 50, 285-290. (16) Van Craen, M.; Verlinden, J.; Gijbels, R.; Adams, F. Talanta, in press. I
RECEIVED for review November 2,1981. Resubmitted April 2,1982. Accepted May 10,1982. M. Van Craen is indebted to the Belgian “Instituut tot Aanmoediging van het Wetenschappelijk Onderzoek in Nijverheid en Landbouw (I.W.O. N.L.)” for financial support. This work was carried out under research grant 80/85-10 of the Interministrial Commission for Science Policy, Belgium.
Analysis of Chrysotile Asbestos in Bulk Materials David 0. Bush” Health, Safety, and Human Factors Laboratory, Eastman Kodak Company, Kodak Park, Rochester, New York 14650
Richard A. Schumacher Industrlal Laboratory, Eastman Kodak Company, Kodak Park, Rochester, New York 14650
A quantltatlve method for the analysls of chrysotile asbestos In bulk materlals uslng thermal evolution analysls has been developed. The amount of chrysotile in a sample Is determined by measurlng the evolved water, using a DuPont molsture evolution analyzer, resuitlng from dehydration at about 840 O C . The method uses 10-20-mg samples and is quantltatlve (f5%) for chrysotlle in materials such as flreprooflng, Insuiatlon, and celling tile. By modlflcation of the DuPont molsture analyzer a temperature program could be applied which yields a qualltatively slgniflcant water loss/ temperature profile.
The analysis of asbestos has become important in recent years as the harmful nature of the mineral fiber has been more fully recognized (1, 2). The ability to quantify the amount of asbestos in the many products which contain the material is important in determining potential exposure. The identification and quantification of asbestos are confounded by the fact that at least six asbestos minerals have been used commercially: chrysotile, anthophyllite, amosite, 0003-2700/82/0354-1792$01.25/0
crocidolite, tremolite, and actinolite (3). The type of asbestos most often associated with asbestos-related diseases is chrysotile. It is therefore not only desirable to be able to specifically measure chrysotile asbestos in a wide variety of commercial products but in other forms of asbestos as well. Potential interference from other types of asbestos is minimized, however, by the fact that 90-95% of all asbestos mined is chrysotile (3). For the quantitative measurement of chrysotile asbestos, X-ray diffraction techniques have received considerable use (4-9). X-ray methods have several recognized drawbacks, however, including laborious sample preparation, interferences from other minerals as well as other asbestos types, and poor precision resulting from nonhomogeneous sample preparation, in addition to the expensive equipment required for analysis (4-8).
Differential thermal analysis (DTA) has been proposed as a quantitative method of analysis for chrysotile in bulk s a m ples (7, 10-13). The method is based on the measurement of the DTA peak corresponding to the exothermic recrystallization of chrysotile to forsterite at about 830 “C. An alternative approach using the DTA method is to measure the 0 1982 Amerlcan Chemlcal Society
ANALYTICAL CHEMISTRY, VOL. 54, NO. 11, SEPTEMBER 1982
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Table I. Water Content, of Five U.I.C.C. Standard Reference Samples % water
sample
country of origin asbestos group
Canada chrysotile Rhodesia chrysotile crocidolite South Africa South Africa amosite anthophyllite Finland Standard deviation s = 0.25% H20.
serpentine serpentine amphibole amphibole amphibole
enthalpy of the endothermic dehydration at about 640 "C associated with the losci of 2 mol of water from chrysotile (Mg,(Si,O,)(OH),). The endothermic dehydration peak appears to be of a greater magnitude allowing for more sensitive measurements of chrysotile. However, conventional DTA has been recognized as a relatively imprecise quantitative tool due to the variable effects of thermocouple placement and sample geometry (14). This paper describes a novel method for the quantitative measurement of chrysotile asbestos in bulk samples. The principle of the method involves the thermal dehydration of chrysotile. The evolved water is measured accurately with a high-temperature moisture evolution analyzer. The chrysotile content of sample is calculated from the measurement of water loss through the dehydration temperature range expressed as a fraction of the observed water loss of a pure sample of chrysotile.
EXPERIMENTAL SECTION Apparatus. A Tracor Low temperature asher, Model LTA 600 L, and a DuPont moisture evolution analyzer (MEA), Model 26-321 AMA, were used. In the later stages of this work the DuPont MEA was modified so that an increase in temperature could be applied to the sample with time via a pulley connected to a mechanical timer. Typically, an indicated temperature increase from 200 to 900 "C was obtained in about 25 min. Unfortunately, this equipment did not apply a truly linear temperature ramp; the temperature ramp is less steep above 600 OC. A more sophisticated change in this equipment would allow the application of an exactly linear temperature ramp. When a temperature ramp was applied to a sample, the output of the instrument was recorded with a DuPont single pen X-Y recorder (992009-901). The resulting water loss/temperature profile is reproducible if the sample size and analysis and recording conditions are kept constant. The total water loss from the sample, equivalent to the area under the profile, is digitally displayed on the instrument. The DuPont MEA wa!3 calibrated with 10-20 mg of sodium tungstate dihydrate each day of use. The temperature scale oln the DuPont MEA was calibratedwith a Digitec thermocuple thermometer, Model 590-KC (made by United Systems Corp.). The results follow:
DuPont MEA, "C
actual temp, "C
200
226
400 600
455 685 925
800
All the temperatures reported in this paper are indicated temperatures and have to be corrected to give actual temperatures. A Waring blender, in a ventilated hood, was used to masticate some of the bulk samples in order to ensure representative sampling. (CAUTION: This process may produce a fine dust. Care should be used in working ,with such samples so that none of the dust is inhaled.) Materials. Two samples of Johns-Manville asbestos (Lots 7RF02 and 7MF5) were used throughout this work. These commercial materials were urged as purchased except for low-temperature ashing. No effort was made to make them more homogeneous. Five U.I.C.C. Standard Reference Asbestos samples of chrysotile (Canada), chrysotile (Rhodesia), crocidolite (South
approx composition (15)
approx ( 8 )
founda
Mg,( si 2 0 5 )(OH)4 Mg,(Si,O,)(OH), Na,Fe,(Si,O,, )(OH),(F), Fe,Mg,(Si*O*2 )(OH), Mg,Fe,(Si,O,,)(OH),(F),
11.4-12.9 11.4-1 2.9 2.5-4.5 2.5-4.5 1.0-6.0
12.58 11.74 1.63 1.37 2.62
Africa),amosite (South Africa), and anthophyllite (Finland) were purchased from Duke Scientific Corp., Palo Alto, CA. Sodium tungstate was purchased from Mallinkrodt 4159, Lot J-1. Diatomite (Kieselguhr) was purchased from E. Merck AG (Lot F740). Calcite was purchased from Wards Natural Science Establishment, Rochester, NY. Ceramfab and Zetex were obtained from DuPont. The ceiling tiles, mica, vermiculite, talc, perlite, gypsum, and mineral wool were all commercial grade materials. A series of homogeneous standard samples of known asbestos content were made by dispersion of weighed mixtures in hexane of an asbestos-freeceiling tile (47-09)and Johns.Mansville asbestos 7MF5 in an explosion-proof Waring blender. The solids were recovered from the hexane by filtration, dried in a vacuum oven at 60 "C, and ashed overnight in the low-temperature asher. Procedure. A 15-mg sample is dried in a nickel boat in the instrument at 200 "C for 20 min. If the instrument is operated manually, the temperature is advanced rapidly to 800 "C and the water lost from the sample is noted for the next 20 min. If the instrument has been modified to apply the temperature ramp automatically, the total amount of water lost from the sample between 200 and 800 "C is recorded against time (temperature). The amount of water in the sample is calculated after subtracting the value for an empty boat. The measured water content is converted to percent chrysotile assuming chrysotile contains 12.58% water. The precision of the method obtained by making replicate analyses of commercial asbestos is 5% (1 standard deviation).
RESULTS AND DISCUSSION The dehydration reaction of chrysotile is approximated in the following equation:
-
Mg3(Siz05)(OH)4 chrysotile
A
2Hz0 + Mg2Si04 forsterite
In this work the water lost between 200 and 800 "C is taken as a measure of chrysotile content. The electrolytic cell in the DuPont MEA is susceptible to contamination by materials which will react with or coat P,Ob The removal of carbonaceous and sublimable material in the asbestos samples can be effected by low-temperature ashing, thus extending the life of the electrolytic cell. The low-temperature ashing (at about 150 "C) has no effect on the water content of asbestos. Five samples of U.I.C.C. Standard Reference Asbestos samples were analyzed by the MEA for their water content (Table I). Chrysotile contains markedly more water than the three amphiboles examined, yet the latter must still be considered as "interferences" in a method for chrysotile based on water content alone. Two samples of commercial Johns-Mansville asbestos were analyzed for their water content between the indicated temperatures of 200 and 800 "C. Lot 7RF02 contained 11.71% HzO (s = 0.67%); lot 7MF5 contained 11.97% H,O. The standard deviation in the standardization of the MEA with sodium tungstate dihydrate is 1.5%. The standard deviation in the above analysis of asbestos samples is 6.8%. This difference in precision is probably due to the fact that asbestos is a natural product and is not homogeneous. Even though a 15-mg sample is used, it is difficult to obtain samples representative of the whole.
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Table 11. Analysis of Known Mixtures of Johns-Manville 7RF02 Asbestos and Asbestos- Free Ceiling Tilea % asbestos av % H,O ( n = 4) 100 80 60 40 20 0
11.71, 10.09, 7.79, 5.94, 3.79, 1.33,
s = 0.67 s = 0.48 s = 0.17 s = 0.26 s = 0.34 s = 0.22
a Standard deviation of the method from the above data = 0.40% H,O.
Table 111. Water Content of Potential Interferants in the Method for Chrysotile no. of water analy- content, material composition ses % mica complex hydrous 2 4.22 aluminosilicates 3.60 vermiculite (Mg,Ca)o. ,(Mg,Fe,Al),- 4 [ (Al,Si),O20 NOH 1,. 8H,O 2 1.53 talc Mg3(Si4010)(0H)2 perlite volcanic glass 2 0.50 2 gypsum CaSO ,.2H 0 0.45 mineral wool cooled slag 2 0.12 calcite CaCO
