Page:NIOSH Manual of Analytical Methods - 7506.pdf/3

 BORON CARBIDE: METHOD 7506, Issue 2, dated 15 August 1994 - Page 3 of 7 SAMPLING: 1. 2.

3.

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% with a HD cyclone for a total sample size of 100 to 1000 L. Do not exceed 2 mg dust loading on the filter. NOTE 1: Do not allow the sampler assembly to be inverted at any time. Turning the cyclone to anything more than a horizontal orientation may deposit oversized material from the cyclone body onto the filter. NOTE 2: For determination of total boron carbide, sample on the PVC filter, without cyclone, at 1 to 4 L/min. Take a bulk dust sample (e.g., 1 m 3 at 4 L/min).

SAMPLE PREPARATION: 4.

5. 6.

7.

Prepare the high-volume respirable dust or settled dust sample for qualitative analysis. Transfer to a filter and XRD sample holder by: (1) ashing and redepositing as described below for personal samples, (2) removing part of the dust from a thickly-coated sample and redepositing it, or (3) mounting all or part of the collection filter on the holder. The settled dust may be ground and/or wet sieved to best match the airborne dust exposure. Wet-sieving is done with a 10-µm sieve, 2-propanol, and an ultrasonic bath, followed by evaporation of excess alcohol, drying in an oven for 2 h, and overnight storage in a dessicator. Deposit the end product on a filter or pack in a conventional XRD powder holder and follow step 10. NOTE: For quantitative determination of percent boron carbide, weigh out, in triplicate, 2 mg of the respirable or sieved dust, transfer to a 50-mL beaker, add 10 mL 2-propanol, and continue with steps 6 and 7. Place the filters in 50-mL beakers in the low temperature asher. Ash according to manufacturer's instructions. After ashing, carefully add 15 mL 2-propanol to each beaker. Cover the beaker with a watchglass. Agitate in an ultrasonic bath for at least 3 min (until agglomerated particles are broken up). 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. Control 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 vacuum on after filtration to produce a dry filter. Remove the filter with forceps and mount it in the XRD sample holder.

CALIBRATION AND QUALITY CONTROL: 8.

9.

Select six silver membrane filters randomly from the same box of filters used for depositing the samples. These will be used as media blanks to correct for sample self-absorption. Mount each media blank on the filtration apparatus and apply vacuum to draw 5 to 10 mL 2-propanol through the filter. Remove and let dry. Determine the net normalized intensity for the silver peak, ˆIAgo, for each media blank (step 11). Average the values for the six media blanks. Prepare and analyze working standard filters. a. Weigh 10- and 100-mg portions of boron carbide to the nearest 0.01 mg. Quantitatively transfer each to a 1-L glass-stoppered bottle using 1.00 L 2-propanol. b. Suspend the powder in 2-propanol using an ultrasonic probe or bath for 20 min. Immediately move the flask to a magnetic stirrer and add a stirring bar. Cool to room temperature before use. c. Mount a silver filter on the filtration apparatus. Place 2 to 4 mL 2-propanol on the filter. Turn off the stirrer and shake the suspension vigorously by hand. Immediately withdraw an aliquot from the center of the suspension. Do not adjust volume in the pipet by expelling NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94