Page:NIOSH Manual of Analytical Methods - 9000.pdf/3

 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