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Anal. Chem. 1982, 54, 2140-2142
Determination of Microgram Amounts of Asbestos in Mixtures by Infrared Spectrometry G. A. Luoma," L. K. Yee, and R. Rowland Department of Natlonal Defence, Defence Research Establishment Paclflc, CFB Esquimalt, British Columbia, Canada VOS 180
The inhalation of asbestos particles has been found to cause a number of serious illnesses among mine workers. The major illnesses, asbestosis and mesothelioma, are caused by the direct inhalation of asbestos fibers into the throat and lungs (1, 2). Other experiments suggest that certain types of asbestos belonging to the amphibole class (amosite, crocidolite, and anthophyllite) are potentially more dangerous than those belonging to the serpentine class (chrysotile) (3,4). This latter observation is directly related to particle size and shape, since amphiboles are usually composed of larger, needlelike fibers which can cause more tissue damage. As a result, determination of asbestos types and concentrations in working environments is necessary to assess potential harmful effects. Although many asbestos substitutes are currently available, the complete replacement of asbestos has not been achieved (5, 6). At present, asbestos is still used in such products as fire blankets, lagging materials for heat pipes and electronics, gaskets, and cement. About 3.5 million tons of asbestos is consumed each year, so methods for its identification are still required. Much recent experimentation concerned with developing positive detection of small amounts of asbestos has been carried out. The major methods used are polarized light microscopy, X-ray diffraction, and scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEMEDS) (7-10). Other less common methods include thermal methods such as differential scanning calorimetry (DSC) and Raman spectroscopy (11,12). All of these techniques produce very good qualitative, and sometimes quantitative, results for specific analyses, but none has been shown to be generally applicable to all asbestos analyses. Furthermore, some are time-consuming and not truly confirmatory (e.g., light microscopy), while others require fairly large sample volumes (e.g., X-ray diffraction) or specialized equipment (e.g., SEMEDS). Therefore, a fast identification technique having a wide general applicability and requiring only small samples is required. A number of infrared studies of asbestos have been reported (13-16). Patterson and O'Connor (13) originally showed that amosite and crocidolite contain strong and characteristic Si0 infrared absorption bands at 1200-900 cm-l, and these bands were also found for chrysotile by Beckett et al. (14). For chrysotile asbestos, a further characteristic sharp OH peak a t 3670 cm-' was also reported (15). Finally, the region between 800 and 200 cm-l was shown to contain a characteristic pattern of peaks which could be successfully used to classify asbestos types (16). Also, quantitative infrared studies on samples of 10-100 pg of the individual asbestoses have been performed (16-18). However, the desire to detect a single small fiber in airborne samples suggests that detection limits of 10 pg or less are necessary. Although the use of infrared spectrometry for the quantitative detection of small amounts of pure asbestos species is well-known, the use of infrared spectrometry for the anaysis of mixtures containing asbestos has been hampered by the presence of interfering bands of the nonasbestos matrix (15). However, the advent of low-priced computer subtraction and multiple scanning abilities has resulted in increased use of infrared spectrometry for identification of components in mixtures (16). Therefore, infrared spectrometric identification and quantification of asbestos in largely nonasbestos mixtures is possible. This report demonstrates that a low-priced in0003-2700/82/0354-2140$01.25/0
frared spectrophotometer equipped with a minicomputer can quantitatively identify microgram amounts of asbestos in a variety of commonly encountered mixtures. The results indicate that infrared sensitivity and selectivity are sufficient for most analyses, while ease of sample handling, speed of analysis, lower cost of equipment, and often superior ability to identify components in mixtures can make it the method of choice.
EXPERIMENTAL SECTION Samples of pure asbestos were obtained from Duke Scientific (Palo Alto, CA). Infrared spectra of these samples were obtained on a Perkin-Elmer Model 398 dispersive infrared spectrophotometer equipped with a Model 3600 data station and a Model 660 printer. Standard concentrations were prepared by mixing 1.00 mg of the asbestos in 100 mg of KBr and diluting successively with KBr to obtain desired concentrations. Exactly 3.00 mg of each sample was loaded into a 3 mm diameter die set and pressed at a constant pressure to form the pellets used to obtain infrared spectra. A Perkin-Elmer beam condenser was also employed during the analyses. For samples containing large amounts of organic nonasbestos components, the samples were first pretreated in sulfuric acid (6 M) and then in aqueous ammonia (15 M), followed by washing with acetone and oven-drying for approximately 2 h at 120 "C. The latter procedure was found (1) to eliminate many organic components, (2) to allow individual asbestos fibers to be isolated, and (3) to remove excess adsorbed water which may interfere with infrared analyses. RESULTS AND DISCUSSION (A) Identification and Quantification of Asbestos Types by Their Infrared Spectra. As mentioned previously, all four of the asbestos types considered here have unique crystal structures which have been shown to produce the characteristic infrared spectra contained in Figure 1. Included in this figure are arrows indicating the infrared bands most useful for quantitative measurements. For a more detailed comparison see references (17, 18). By utilization of the the entire infrared region between 4000 and 400 cm-l the various types of asbestos are readily identified, even in mixtures. Also, a comparison of the infrared spectra of asbestoses to common nonasbestos substitutes indicates that the two groups are readily distinguishable (19). The characteristic bands mentioned above can also be used to determine the four asbestos types quantitatively and to estimate the lower detection limit of each asbestos type. The present study indicates, for each asbestos type, linearity of absorbance vs. asbestos amount is achieved for samples ranging from 1pg to 30 pg. Thus, the infrared technique using a low cost instrument can be used to estimate the quantity of asbestos in very small samples. Although the lowest amount of asbestos examined in the present study was 1.5 pg for chrysotile and amosite varieties, the infrared technique could be extended by using multiple scans or by employing a micropellet accessory (1 mm pellet) to identify as little as 100 ng of asbestos. Using more sensitive (but more expensive) dispersive instruments could further reduce the detection limit. Finally, the use of Fourier transform infrared spectrometry by this laboratory suggests that less than 10 ng of asbestos is detectable. (B) Identifying and Quantifying Mixtures of Asbestos. In a test of the ability of infrared spectrometry to identify and quantify the components of mixtures of more than one as-
Published 1982 by the American Chemical Society
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Flgure 2. The spectrum of an actual mixture of anthopyllite and chrysotile (a) and the best match computer simulated spectrum obtained by summing individual anthopyllite and chrysotile spectra (b).
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infrared spectra of the four major asbestos types in the region 4000-400 cm-': (a) chrysotile; (b) amosite; (c) anthophyllite; (d) crocidolite. Flgure 1. The
bestoe type, two samples were studied one a synthetic mixture of 5.5 pg of chrysotile and 18pg of anthophyllite; and the other an unknown mixture of amosite, chrysotile, and a nonasbestos material. Figure 2a shows that the spectrum of the mixture of chrysotile and anthophyllite displays features characteristic of a mixture of these two asbestos types. The strong doublet at 3680 and 3630 cm-l is indicative of the presence of chrysotile. Further, since anthophyllite contains only a weak band in this region, the intensity of this peak can be used to estimate the quantity of chrysotile present. When the intensity of the 3680-cm-' peak is compared to standard calibration curves, the estimated amount of chrysotile is 5.5 pg, exactly the amount which was known to be present. 'I'herefore, for many samples no computer manipulation is necessary. The strong infrared band at 669 cm-l is indicative of the presence of anthophyllitt? asbestos, which is the only asbestos
type with an absorption band in that region. The intensity of this band corresponds to the presence of 19.5 pg of anthophyllite. This value is slightly higher than the known amount (18 pg) and is likely due to added intensity from the broad overlapping chrysotile band centred at 600 cm-'. Although for the present study the comparisons were made by hand, the minicomputer could easily perform the analysis automatically while subtracting out the interferences from the chrysotile band. Figure 2b shows that best match spectrum obtained by summing individual chrysotile and anthophyllite spectra. This simulated spectrum was composed by mixing 22% chrysotile and 78% anthophyllite from computer-stored spectra of each asbestos type. Thus, a computer simulation can also be used to estimate the proportions of each asbestos type, and again can be done automatically by the minicomputer. As a test of the ability of infrared spectrometry to identify and quantify asbestos mixtures in samples containing other inorganic components, a sample of lagging material of unknown composition was analyzed (Figure 3a). The results obtained by infrared analysis were checked by X-ray diffraction for confirmation of findings. The strong absorption at 3680 cm-l indicates the presence of chrysotile asbestos in the sample. Further evidence is provided by the broad band at 600 cm-' and the strong absorption at 435 cm-l. As well as confirming the presence of chrysotile, the presence of an amphibole is suggested by the peak at 770 cm-'. The amphibole can be identified as amosite by the presence of peaks at 700,900, and 1128 cm-', as well as by the broad strong absorption at 480 cm-l. The final major component of the mixture was determined by means of the shoulder at 800 cm-' and the lack of any non Si-0 bands to be amorphous silica. To determine the proportions of the two asbestoses and silica in the mixture, we simulated the spectrum from spectra of known amounts of the three components (Figure 3b). The simulation indicates that the composition is about 40% chrysotile asbestos, 30% amosite asbestos, and 30% amorphous silica. The presence of both amosite and chrysotile asbestoses was confirmed by X-ray diffraction but the diatomaceous earth cannot be detected because of ita amorphous
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Flgure 3. The Infrared spectra of (a) an unknown sample of lagging material and (b) the best match computer simulated spectrum obtained by summing individual diatomatceous earth, amosite, and chrysotile
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Flgure 4.
The infrared spectrum of an asbestos-impregnated rubber
character. Therefore, for this sample, infrared analysis proved superior for estimating quantities of components in a mixture containing multiple types of asbestos and nonasbestos materials. (C) Determination of Asbestos in Largely Nonasbestos Materials. Since asbestos is often found as a minor component in nonasbestos media (e.g., nonskid deck coatings, gaskets, impurities in talcs), samples of a rubber gasket containing asbestos and a synthetic mixture of 10% chrysotile in amorphous silica were analyzed to determine the utility of infrared spectrometry for largely nonasbestos samples (Figures 4 and 5). For an untreated asbestos/rubber gasket (Figure 4),the infrared spectrum as a KBr pellet confirms the presence of chrysotile asbestos (strong peak at 3670 cm-l, 600 cm-l, 1100-900 cm-’, etc.), as well as the organic rubber (C-H stretches a t 2900 cm-l). The characteristic asbestos bands show very little interference from the rubber. Furthermore, purification by acidlbase and acetone washing (not shown) causes the interference from the rubber to be reduced, pro-
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The spectra of (a) a 10% mixture of chrysotile in diatomaceous earth and (b) the computer subtracted difference spectrum obtained by subtracting the spectrum of diatomaceous earth from (a). Figure 5.
ducing a high-quality spectrum of chrysotile as in Figure la. In the synthetic mixture of 10% chrysotile in amorphous silica (Figure 5a), the presence of chrysotile asbestos is again indicated by the peak at 3670 cm-l but cannot be confirmed because of the strong interference from the Si-0 bands of amorphous silica. However, by carefully computer subtracting the spectrum of amorphous silica from this “mixture”, the difference spectrum can be positively identified as chrysotile (Figure 5b). Therefore, the infrared technique can also be used on samples which contain asbestos as only a minor component, if proper care in sample preparation is performed.
LITERATURE CITED
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(1) Becklake, M. R. Am. Rev. Respir. Dis. 1978, 114, 187-203. (2) Tlmbrell, V. Ann. N . Y . Acad. Sci. 1985, 732, 255-273. (3) Harrington, J. S.;Gilson, J. C.; Wagner, J. C. Nature (London) 1971,
232,54-55. (4) Timbrell, V.; Grlffiths, D. M.; Pooley, F. D. Nature (London) 1971, 232, 55-56. (5) “Asbestos Properties”; Duke Scientific: Palo Alto, CA, 1979. (6) Department of National Defence Canada, Specification #D-03-011001/SF-000; Ottawa, Canada, April 1, 1980. (7) McCrone, W. C. Mlcroscope 1977, 28, 251-264. (8) McRae, K. I.; Waggoner, C. A. Defence Research Establishment Paclflc Technical Memorandum, 80-10,1980. (9) Lange, B. A.; Haartz, J. C. Anal. Chem. 1973, 45,809-811. (IO) Rickards, A. L. Anal. Chem. 1978, 50, 892-898. (11) . . Hamer. D. H.; Folie. F. R.: Shelz. J. P. Am. Ind. Hva. Assoc. J. 1078, 37, 296-304: (12) Blaha, J. J.; Rosasco, G. J. Anal. Chem. 1978, 50, 892-898. (13) Paterson, J. H.; O’Connor, D. J. Aust. J . Chem. 1985, 79, 7. 155-7 ... . 764. . .. (14) Beckett, S. T.; Middleton, A. P.; Dodgson, J. Ann. Occup. Hyg. 1975, 78.313-320. (15) Baglonl, R. P. Envlron. Scl. Techno/. 1975, 9 ,262-263. (18) Coates, J. P. Perkin Elmer InfraredBull. 1978, IR147. (17) Coates, J. P. Am. Lab. (Fairfield, Conn.) 1977, 9 , (ll), 105-111. (18) Coates, J. P. Am. Lab. (Fairfleld, Conn.) 1977, 9 (12),57-85. (19) Luoma. 0. A.; Yee, L. K.; Rowland, R. Defence Research Establlshment Pacific Materials Report, 81-D, 1981.
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RECEIVED for review November 23, 1981. Accepted July 9, 1982.
