ASBESTOS, CHRYSOTILE by XRD
Mg3Si2O5(OH)4
MW: ca. 283
METHOD: 9000, Issue 2
EPA Standard (Bulk):
CAS: 12001-29-5
9000
RTECS: CI6478500
EVALUATION: FULL
1% by weight
PROPERTIES:
Issue 1: 15 May 1989 Issue 2: 15 August 1994
solid, fibrous mineral; conversion to Forsterite at 580 °C; attacked by acids; loses water above 300 °C
SYNONYMS: Chrysotile
SAMPLING BULK SAMPLE:
1 to 10 grams
SHIPMENT:
seal securely to prevent escape of asbestos
SAMPLE STABILITY:
indefinitely
BLANKS:
none required
ACCURACY RANGE STUDIED: 1 to 100% in talc [1] BIAS:
negligible if standards and samples are matched in particle size [1]
ˆ ): OVERALL PRECISION (S rT
unknown; depends on matrix and concentration
ACCURACY:
± 14% to ± 25%
MEASUREMENT TECHNIQUE:
X-RAY POWDER DIFFRACTION
ANALYTE:
chrysotile
PREPARATION:
grind under liquid N 2; wet-sieve through 10-µm sieve
DEPOSIT:
5 mg dust on 0.45-µm Ag membrane filter
XRD:
Cu target X-ray tube; Optimize for intensity; 1° slit; Integrated intensity with background subtraction
CALIBRATION:
suspensions of asbestos in 2-propanol
RANGE:
1 to 100% (w/w) asbestos
ESTIMATED LOD: 0.2% asbestos in talc and calcite; 0.4% in heavy X-ray absorbers such as Fe 2O 3 PRECISION (Sr):
0.07 (5 to 100%); 0.10 (@ 3%); 0.125 (@ 1%)
APPLICABILITY: Analysis of percent chrysotile asbestos in bulk samples.
INTERFERENCES: Antigorite (massive serpentine), Chlorite, Kaolinite, Bementite, and Brushite interfere. X-ray fluorescence and absorption is a problem with some elements; fluorescence can be circumvented with a diffracted beam monochromator, a nd absorption is corrected for in this method.
OTHER METHODS: This is P&CAM 309 [2] applied to bulk samples only, since the sensitivity is not adequate for personal air samples. The EPA Test Method for the determination of asbestos in bulk insulation samples is similar to this one [3]. Me thod 7400 is an optical counting procedure for airborne fibers in personal samples. Methods 7402 (Asbestos by Transmission El ectron Microscopy) and 9002 (Asbestos by Polarized Light Microscopy) are also useful for positive identification of asbestos.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 CHRYSOTILE ASBESTOS (BULK): METHOD 9000, Issue 2, dated 15 August 1994 - Page 2 of 6 REAGENTS: 1.
2. 3. 4.
EQUIPMENT:
Chrysotile*, available from: Analytical Reference Minerals, Measurements Research Branch, DPSE, NIOSH, 4676 Columbia Parkway, Cincinnati, OH 45226; or UICC Asbestos Reference Sample Set, UICC MRC Pneumoconiosis Unit Llandough Hospital, Penarth, Glamorgan, CF6 1XW, UK.2. 2-Propanol.* Desiccant. Glue or tape for securing Ag filters to XRD holders.
See SPECIAL PRECAUTIONS.
1. Vials, plastic (for bulk sample). 2. Freezer mill, liquid N 2-cooled, (Spex Model 6700 or equivalent), grinding vials (Spex 6701), extractor (Spex 6704). 3. Ultrasonic bath. 4. Sieve, 10-µm, for wet-sieving. 5. Filters, polycarbonate, 1.0-µm, 37-mm (Nuclepore or equivalent). 6. Filtration apparatus and side-arm vacuum flask with 25- and 37-mm filter holders. 7. Oven, drying, 110 °C. 8. Analytical balance, readable to 0.01 mg. 9. Beaker, Griffin, 50-mL, with watchglass cover. 10. Filters, silver membrane, 25-mm diameter, 0.45-µm pore size (Millipore Corp., Poretics Corp., or equivalent). 11. Desiccator. 12. Bottles, glass, 1-L, with ground glass stoppers. 13. Wash bottle, polyethylene. 14. Magnetic stirrer. 15. X-ray powder diffractometer with copper target x-ray tube and scintillation detector. 16. Reference specimen (mica, Arkansas stone or other stable standard) for data normalization. 17. Volumetric pipettes and flasks.
SPECIAL PRECAUTIONS: Asbestos, a human carcinogen, should be handled in a hood [4]. 2-Propanol is flammable.
SAMPLING: 1.
Place several grams of the dust to be analyzed in a plastic vial, seal the vial securely and ship in a padded carton.
SAMPLE PREPARATION: 2. 3.
4.
Place ca. 0.5 g of sample dust in a grinding vial and grind in a liquid nitrogen-cooled mill for 2 to 10 min. Wet sieve the ground dust using a 10-µm sieve and 2-propanol. Place the dust on the sieve and place the sieve directly in an ultrasonic bath or in a wide dish in the bath. Use enough 2-propanol to cover the dust (put water in the bath if a dish is used to contain the 2-propanol). Apply ultrasonic power to sieve the dust. NOTE: It may take some time to obtain several mg of dust. Heating of the 2-propanol is likely and cooling periods may be required. Recover the sieved sample dust from the 2-propanol by filtering the suspension through a non-fibrous filter (polycarbonate) or by driving off the 2-propanol on a hot plate. Dry the sieved sample in 110 °C oven for 4 h or more.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 CHRYSOTILE ASBESTOS (BULK): METHOD 9000, Issue 2, dated 15 August 1994 - Page 3 of 6 9 5.
6.
7.
8.
Weigh out ca. 5 mg of the sieved material onto a small square of tared weighing paper. Record the actual weight, W, to the nearest 0.01 mg. Transfer the dust to a 50-mL beaker, washing the weighing paper with several mL of 2-propanol. Add 10 to 15 mL 2-propanol to the beaker. Cover the beaker with a watchglass. Agitate in an ultrasonic bath at least 3 min until all agglomerated particles are dispersed. Wash the underside of the watchglass with 2-propanol, collecting the washings in the beaker. Place a silver filter in the filtration apparatus. Attach the funnel securely over the entire filter circumference. With no vacuum, pour 2 to 3 mL 2-propanol onto the filter. Pour the sample suspension from the beaker into the funnel and apply vacuum. During filtration, rinse the beaker several times and add rinsings to the funnel. NOTE: Control the filtration rate to keep the liquid level in the funnel near the top during rinsing. Do not wash the walls or add 2-propanol to the funnel when the liquid level is lower than 4 cm above the filter. Leave the vacuum on after filtration for sufficient time to produce a dry filter. Remove the filter with forceps and attach it to the sample holder for XRD analysis.
CALIBRATION AND QUALITY CONTROL: 9.
Prepare and analyze working standard filters: a. Prepare two suspensions of chrysotile asbestos in 2-propanol by weighing 10 and 100 mg of the dry powder to the nearest 0.01 mg. Quantitatively transfer each to a 1-L glass-stoppered bottle using 1.00 L 2-propanol. NOTE: Depending on the particle size of the standard, it may need to be ground and wet sieved (step 3). Dry the standards in a 110 °C oven for 4 h or more. Store in a desiccator. b. Suspend the powder in the 2-propanol with an ultrasonic probe or bath for 20 min. Immediately move the flask to a magnetic stirrer with thermally-insulated top and add a stirring bar to the suspension. Cool the solution to room temperature before withdrawing aliquots. c. Mount a filter on the filtration apparatus. Place several mL 2-propanol on the filter surface. Turn off the stirrer and shake vigorously by hand. Within a few seconds of setting the bottle down, remove the lid and withdraw an aliquot from the center of the 10 or 100 mg/L suspension. Do not adjust the volume in the pipet by expelling part of the suspension. If more than the desired aliquot is withdrawn, return all of the suspension to the bottle, rinse and dry the pipet, and take a new aliquot. Transfer the aliquot from the pipet to the filter. Keep the tip of the pipet near the surface but not submerged in the delivered suspension. d. Rinse the pipet with several mL 2-propanol, draining the rinse into the funnel. Repeat the rinse several more times. Prepare working standard filters, in triplicate, by this technique, at e.g., 0, 20, 30, 50 100, 200 and 500 µg. e. Apply vacuum and rapidly filter the suspension. Leave vacuum on until filter is dry. Do not wash down the sides of the funnel after the deposit is in place since this will rearrange the material on the filter. Transfer the filter to the sample holder. f.
Analyze by XRD (step 12). The XRD intensities (12.d.) are designated
and are then
normalized (12.e.) to obtain . The intensities for standards greater than 200 mg should be corrected for matrix absorption (12.f. and 13). g.
h.
Prepare a calibration graph by plotting , as a function of µg of each standard. NOTE: Poor repeatability (greater than 10% above 0.04 mg chrysotile) indicates that new standards should be made. The data should lie along a straight line. It is preferable to use a weighted least squares with 1/ σ2 weighing, where σ2 is the variance of the data at a given loading. Determine the slope, m, of the calibration curve in counts/µg. The intercept on the abscissa should be within ±5 µg of zero.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 CHRYSOTILE ASBESTOS (BULK): METHOD 9000, Issue 2, dated 15 August 1994 - Page 4 of 6 NOTE: A large intercept indicates an error in determining the background, i.e., an incorrect baseline has been calculated or interference by another phase. Select six silver membrane filters as media blanks (for determination of sample self-absorption, step 13) randomly from the same box of filters to be used for depositing the samples. Mount each of the media blanks on the filtration apparatus and apply vacuum to draw 5 to 10 mL of 2-propanol through the filter. Remove, let dry and mount on sample holders. Determine the net
10.
normalized count for the silver peak, value for the six media blanks.
, for each media blank (step 12). Obtain an average
MEASUREMENT: 11.
Obtain a qualitative X-ray diffraction scan (e.g., 10 to 80 degrees 2-theta) of the sample to determine the presence of chrysotile and interferences. The expected diffraction peaks are as follows:
Mineral Chrysotile Silver 12.
Peak (2-Theta Degrees) Primary Secondary 12.08 38.12
24.38 44.28
Mount the filter (sample, standard or blank) in the XRD instrument and: a. Determine the net intensity, I r, of the reference specimen before each filter is scanned. Select a convenient normalization scale factor, N, which is approximately equivalent to the net count for the reference specimen peak, and use this value of N for all analyses. b. Measure the diffraction peak area of a chrysotile peak that is free of interference. Scan times should be long, e.g., 15 min. c. Measure the background on each side of the peak for one-half the time used for peak scanning. The sum of these two counts is the average background. Determine the position of the background for each sample. d. Calculate the net intensity, I x (the difference between the peak integrated count and the total background count). e. Calculate and record the normalized intensity, Î x, for the sample peak on each sample and standard:
f.
g.
NOTE: Normalizing to the reference specimen intensity compensates for long-term drift in X-ray tube intensity. If intensity measurements are stable, the reference specimen may be run less frequently; net intensities should be normalized to the most recently measured reference intensity. Determine the net count, I Ag, of an interference-free silver peak on the sample filter following the same procedure. Use a short scan time for the silver peak (e.g., 5% of scan time for analyte peaks) throughout the method. Scan each field blank over the same 2-theta range used for the analyte and silver peaks. These analyses serve only to verify that contamination of the filters has not occurred. The analyte peak should be absent. The normalized intensity of the silver peak should match that of the media blanks.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 CHRYSOTILE ASBESTOS (BULK): METHOD 9000, Issue 2, dated 15 August 1994 - Page 5 of 6 CALCULATIONS: 13.
Calculate the percentage of chrysotile in the bulk dust sample:
where: Îx = normalized intensity for sample peak b = intercept of calibration graph ( vs. W) m = slope of calibration graph (counts/µg) f(T) =
= absorption correction factor (Table 1)
R = sin ( T = Î Ag/(average ) = transmittance of sample ÎAg = normalized silver peak intensity from sample average
= normalized silver peak intensity from media blanks (average of six
values) W = mass of deposited sample in µg. NOTE: For a more detailed discussion of the absorption correction procedure, see references [5] to [8].
EVALUATION OF METHOD: This method is based on the work of B.A. Lange in developing P&CAM 309 [1,2]. Samples in the range of 1 to 100% chrysotile in talc were studied to establish the feasibility of an XRD method for airborne asbestos. Analytical precision was as follows: % Chrysotile in Talc
Sr (%)
100 10 7 5 3 1
6.9 4.7 9.8 8.2 10.1 12.5
This work also showed that bias of results after absorption corrections are made is negligible.
REFERENCES: [1] [2] [3] [4] [5]
Lange, B. A. Determination of Microgram Quantities of Asbestos by X-Ray Diffraction: Chrysotile in Thin Dust Layers of Matrix Material, Anal. Chem., 51:520(1979). NIOSH Manual of Analytical Methods, 2nd ed., V. 5, P&CAM 309, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 79-141 (1979). Perkins, R.L. and B.W. Harvey. U.S. Environmental Protection Agency Test Method for the Determination of Asbestos in Bulk Building Materials, EPA/600/R-93/116 (June, 1993). Criteria for a Recommended Standard...Occupational Exposure to Asbestos (Revised), U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-169 (1976). Leroux, J. and C. Powers. Direct X-Ray Diffraction Quantitative Analysis of Quartz in Industrial Dust Films Deposited on Silver Membrane Filters, Occup. Health Rev., 21:26 (1970). NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 CHRYSOTILE ASBESTOS (BULK): METHOD 9000, Issue 2, dated 15 August 1994 - Page 6 of 6 [6] [7]
Williams, D. D. Direct Quantitative Diffractometric Analysis, Anal. Chem., 31:1841 (1959). Abell, M. T., D. D. Dollberg, B. A. Lange, R. W. Hornung and J. C. Haartz. Absorption Corrections in X-ray Diffraction Dust Analyses: Procedures Employing Silver Filters, Electron Microscopy and X-ray Applications , V. 2, 115, Ann Arbor Science Publishers, Inc. (1981). Dollberg, D. D., M. T. Abell, and B. A. Lange. Occupational Health Analytical Chemistry: Quantitation Using X-Ray Powder Diffraction, ACS Symposium Series, No. 120, 43 (1980).
[8]
METHOD REVISED BY: M. T. Abell, NIOSH/DPSE.
TABLE 1. ABSORPTION CORRECTION FACTOR AS A FUNCTION OF TRANSMITTANCE FOR SOME CHRYSOTILE-SILVER PEAK COMBINATIONS. f( T) Transmittance T 1.00 0.99 0.98 0.97 0.96 0.95 0.94 0.93 0.92 0.91 0.90 0.89 0.88 0.87 0.86 0.85 0.84 0.83 0.82 0.81 0.80 0.79 0.78 0.77 0.76 0.75 0.74 0.73 0.72 0.71 0.70
Chrysotile Silver
12.08 38.12
24.38 38.12
1.0000 1.0157 1.0317 1.0480 1.0647 1.0817 1.0991 1.1168 1.1350 1.1535 1.1724 1.1917 1.2114 1.2316 1.2522 1.2733 1.2948 1.3168 1.3394 1.3624 1.3859 1.4100 1.4346 1.4598 1.4856 1.5120 1.5390 1.5666 1.5949 1.6239 1.6536
1.0000 1.0078 1.0157 1.0237 1.0319 1.0402 1.0486 1.0572 1.0659 1.0747 1.0837 1.0928 1.1021 1.1115 1.1212 1.1309 1.1409 1.1510 1.1613 1.1718 1.1825 1.1933 1.2044 1.2157 1.2272 1.2389 1.2508 1.2630 1.2754 1.2881 1.3010
Transmittance T 0.69 0.68 0.67 0.66 0.65 0.64 0.63 0.62 0.61 0.60 0.59 0.58 0.57 0.56 0.55 0.54 0.53 0.52 0.51 0.50 0.49 0.48 0.47 0.46 0.45 0.44 0.43 0.42 0.41 0.40
f( T) 12.08 24.38 38.12 38.12 1.6839 1.7151 1.7470 1.7797 1.8132 1.8475 1.8827 1.9188 1.9558 1.9938 2.0328 2.0728 2.1139 2.1560 2.1993 2.2438 2.2895 2.3365 2.3848 2.4344 2.4855 2.5380 2.5921 2.6478 2.7051 2.7642 2.8251 2.8879 2.9526 3.0195
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
1.3142 1.3277 1.3414 1.3555 1.3698 1.3845 1.3995 1.4148 1.4305 1.4465 1.4629 1.4797 1.4969 1.5145 1.5325 1.5510 1.5700 1.5895 1.6095 1.6300 1.6510 1.6727 1.6950 1.7179 1.7414 1.7657 1.7907 1.8165 1.8431 1.8705