Page:NIOSH Manual of Analytical Methods - 7504.pdf/3

 VANADIUM OXIDES: METHOD 7504, Issue 2, dated 15 August 1994 - Page 3 of 10 SAMPLING: 1. 2.

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Calibrate each personal sampling pump with a representative sampler in line. Sample at 1.7 ± 5% L/min with a nylon cyclone or 2.2 ± 5% L/min with an HD cyclone for a total sample size of 200 to 1000 L. Do not exceed 2 mg dust loading on the filter. NOTE: Do not allow the sampler assembly to be inverted at any time. Turning the cyclone to more than 90 °C from vertical may deposit over-sized material from the cyclone body onto the filter. Obtain an area high-volume bulk sample in the vicinity of the personal sampling area.

SAMPLE PREPARATION: 4.

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Place sample filter in a centrifuge tube. Add 10 mL THF. Place centrifuge tube in ultrasonic bath for 10 min. NOTE: The filter should dissolve almost instantaneously. Mount a silver filter in the filtration apparatus. Attach the funnel securely over the entire filter circumference. With no vacuum, pour 2 to 3 mL THF onto the filter. Pour the sample suspension from the centrifuge tube into the funnel. Rinse centrifuge tube twice with 5-mL portions of THF, adding rinses to the funnel, and apply vacuum. Control filtration rate to keep liquid level near top of funnel during filtering. Do not wash the walls or add THF to the funnel when the liquid level is lower than 4 cm above the filter. Leave vacuum on after filtration for sufficient time to dry the filter. Transfer filter with forceps to sample holder for XRD analysis.

CALIBRATION AND QUALITY CONTROL: 7.

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Select six silver membrane filters as media blanks, randomly from the same box of filters to be used for depositing the samples. Mount each media blank on the filtration apparatus and apply vacuum to draw 5 to 10 mL THF through the filter. Remove, let dry and mount on XRD holders. NOTE: These will be used to test for sample self-absorption. Prepare standard suspensions. a. Weigh 10- and 50-mg portions of the dry analytes to the nearest 0.01 mg. Quantitatively transfer to 1-L glass-stoppered bottles. Add 1.00 L acetonitrile (for V 2O 5) or isopropanol (for V2O 3 or NH 4VO 3). b. Disperse the powder in the liquid using an ultrasonic probe or bath for 20 min. Immediately move the flask to a magnetic stirrer and add a stirring bar to the suspension. Allow the solution to return to room temperature before withdrawing aliquots. Prepare a series of standard filters over the range 0.05 to 2 mg V per sample. a. Mount a filter on the filtration apparatus. Wet the filter with ca. 3 mL of acetonitrile (for V2O 5) or isopropanol (for V 2O 3 or NH 4VO 3). b. Turn off the stirrer and shake the bottle vigorously by hand. Immediately remove the lid and withdraw an aliquot (2 to 25 mL) from the center of the 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. c. Transfer the aliquot from the pipet to the funnel. Keep the tip of the pipet near the surface but not submerged in the suspension. Rinse the pipet with ca. 5 mL of acetonitrile (for V2O 5) or isopropanol (for V 2O 3 or NH 4VO 3), draining the rinse into the funnel. Repeat the rinse three more times. d. Apply vacuum and rapidly filter the suspension. Leave vacuum on until filter is dry. Do not wash down sides of funnel after deposit is in place (to avoid rearranging the material on the filter). e. Transfer the filter to the XRD sample holder.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94