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||Respirable Coal Mine Dust
||25-250 micrograms of quartz
||August 3, 1989
||November 14, 1994
1 PRINCIPLE OF THE METHOD
1.1 Airborne respirable dust samples are collected on
membrane filters (in capsules pre-weighed to one
hundredth of a milligram, or one thousandth of a
milligram) using MSHA/NIOSH approved personal respirable
dust samplers as described in 30 CFR Part 74.
2 RANGE AND LIMIT OF DETECTION
1.2 After collection, the filter capsules are reweighed to
one hundredth of a milligram in order to determine the net sample mass.C
1.3 The sample filters are ashed in a low-temperature radio-frequency asher to destroy the organic matrix (coal dust and collection filter).
1.4 Ashed samples are deposited onto a 0.64 cm2 circular
area (9 mm diameter) of a DM-450 vinyl/acrylic copolymer filter. (The
use of smaller deposit areas may increase the sensitivity of the analysis. Redeposited
samples to be analyzed for quartz must be of the same deposit diameter as
1.5 The redeposited, ashed dust samples are scanned by infrared spectrometry
between frequencies of 1,000 and 700 cm-1 to determine the quartz and
1.6 The mass of quartz in the deposit is determined (after
correcting for the interference by kaolinite) using calibration data from standard
quartz samples and standard kaolinite samples.
1.7 The percentage of quartz in the samples is calculated using the quartz mass
determined from the analysis and the and the samples mass of dust.
2.1 The range of this method is 25 to 250 micrograms of quartz. The mass required
is 0.45 milligram of respirable coal mine dust if filters are preweighed to
0.01 milligram and 0.100 milligram of dust if preweighed to 0.001 milligram.
2.2 The detection limit of this method (3 time the standard deviation of the analysis
of 10 blank filters) is 3 micrograms quartz.
3.1 Cristobalite, tridymite, kaolinite, and amorphous silica have absorbance peaks at
800 cm-1 . Of these, however, only kaolinite has been detected in coal mine dust.
4 PRECISION AND ACCURACY
3.2 Coal mine dust frequently contains kaolinite. Since kaolinite has an absorption
band at the same frequency as quartz (800 cm-1 ), its presence causes an
overestimation of the quartz mass. However, kaolinite also has an infrared absorbance band
at 917 cm-1 . (The kaolinite absorbance at 917 cm-1 is approximately
eight times that at 800 cm-1 .) The kaolinite content in the sample is determined
from the 917 cm-1 band and the kaolinite contribution to the absorbance at 800
cm-1 is determined from the absorbance of kaolinite at 917 cm-1
using the calibration data. The quartz absorbance is the remainder of the absorbance at
800 cm-1 after subtracting the kaolinite contribution from the total absorbance.
4.1 The error of the low-temperature asher, infrared method for the determination of
quartz mass is between 5 and 10 percent relative standard deviation (RSD in the 100 to
500 microgram quartz range.(1)
5 ADVANTAGES AND DISADVANTAGES OF THE METHOD
4.2 The accuracy of the method may depend on the particle size distribution and purity
of standard materials used in preparation of instrument calibration.
5.1.1 The quartz analysis can be performed on a single sample having a weight gain as
low as 0.100 milligram if the sample is pre- and post-weighed to a thousandth
of a milligram, or a weight gain as low as 0.45 milligram if the sample is weighed to a
hundredth of a milligram.
5.1.2 The detection limit is lower than either the X-ray diffraction method (Anderson
1983) or the Talvitie method (Talvitie 1951, 1958).<
5.1.3 Samples prepared for analysis can also be analyzed using X-ray
diffraction without any additional preparation.
5.1.4 The analytical equipment is considerably less expensive than that required for
The method requires the low-temperature ashing and redeposition of all samples prior to analysis.
6.1 Fourier transform infrared spectrophotometer; PE Model 1750, 1725x or equivalent
with optional sample shuttle accessory.
6.2 Polystyrene film standard (0.05 millimeter thickness); PE No. 186-2082 or equivalent.
6.3 Low-temperature radio-frequency (RF) asher and vacuum pump; LFE Model
LTA-504 or equivalent.
6.4 Oxygen tank and two-stage regulator for low temperature asher, second stage of
regulator capable of being set at 2 to 10 psi.
6.5 Microbalance capable of weighing to 0.001 or 0.01 milligrams; Mettler M-3 or equivalent.
6.6 Filters for sample redeposit; Gelman Instrument Company, DM-450, vinyl/acrylic
copolymer membrane, 47 millimeter diameter, 0.45 micrometer pore size.
6.7 Filters for supporting collection filter during redepositing; Gelman Type A/E
glass fiber filters, 25 millimeter diameter.
6.8 Filtration apparatus consisting of: 3-place manifold, fritted supports and clamps,
rubber stoppers, a 4,000 ml side-arm filtering flask and vacuum tubing.
(See Figure 1 for illustration of this apparatus.)
6.9 Vacuum source (water aspirator or vacuum pump) with trap, (2,000 ml side-arm flask).
(See Figure 1 for illustration of this apparatus.)
6.10 Small, stainless steel forceps for opening filter cassettes and for handling filters.
6.11 Petrislides for 47 millimeter diameter filters; Millipore No. PD15-047-00 or equivalent.
6.12 Ultrasonic bath, 200 watt input.
6.13 Wash bottles, polyethylene, 250 milliliter.
6.14 Beakers, Pyrex, 50 ml, one per sample to be analyzed (Beakers are numbered in
sequence and grouped in lettered sets to prevent mixing of samples, i.e., A1, A2,...A28;
B1, B2,...B28; etc.)
6.15 Diamond Marking Pencil (used to mark numbers on beakers in Section 6.14).
6.16 Aluminum filtering funnels (These are specially fabricated funnels, similar to the
Millipore No. XX10-025-40, and are shown on Figure 2. All funnels used
for calibration and analysis must have the same bore diameter, such as the 9 millimeters
6.17 Desiccator for storing the quartz and kaolinite standard materials.
6.18 Sample holders for infrared instrument (These are specially-made steel plates
with a center hole having a diameter the same as, or slightly smaller than, that of
the sample deposit (9 mm). Small ring magnets are used to hold the filters in position
on the sample holder.)
6.19 Slide warmer (for drying filters after filtering).
6.20 Volumetric pipettes, Class A, Pyrex-type or borosilicate glass, in the following
sizes: 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, and 30 milliliters (for preparing
calibration standards and QA samples).
6.21 Pipette filler, rubber or neoprene.
6.22 Flasks, volumetric, Pyrex-type, with stoppers, 500 and 1,000 milliliter sizes.
6.23 Spatula, micro, stainless steel, (for weighing out quartz and kaolinite standard materials).
6.24 Weighing boats, aluminum, 12 millimeter; Cahn Instruments No. 1187.
7.1 Isopropanol (IPA), technical and ACS reagent grade.
7.2 Quartz for calibration samples; Standard Reference Material(SRM)1878,
"Respirable Alpha Quartz," U.S. Department of Commerce, National Institute
for Standards and Technology, Washington, D.C. or -5 micrometer MINUSIL, Pennsylvania
Glass and Sand Company, Berkeley Springs, West Virginia.
7.3 Kaolinite for calibration samples; Georgia Kaolin, Hydrite UF or equivalent.
8.1 Assemble the numbered beakers, the respirable coal mine dust samples to be analyzed,
and the sample handling data sheet that is obtained from the computer. (See Sample Handling
Procedure-Quartz Lab, April 22, 1993.)
8.2 Using the forceps, remove the collection filter and stainless steel wheel from the
cassette capsule and place them, first the wheel and then the filter with the dust side
down, into the bottom of a numbered beaker.
8.3 Put the beakers containing the samples into the low-temperature asher. With each
run of filters ashed (up to 25), also include three quality assurance (QA) samples.
(See Internal Quality Assessment Program for Quartz Analysis, October 1992 for an
explanation of the QA samples.)
8.4 Ash samples until the filters are completely ashed, approximately 1 hour,
using 300 watts RF power and an oxygen flow rate of approximately 200-300 cc/minute.
(See Standard Operating Procedures Low-Temperature Ashers.) Carefully remove
the glass beakers from the low-temperature asher. As each beaker is removed,
gently rinse the sides with about 10 ml of technical grade IPA using a wash bottle.
Do not squirt the IPA directly at the bottom of the beaker as this will blow the ash out of
8.5 Set-up the filtering apparatus (Section 6.8) as illustrated in Figure 1. Place two
Type A/E glass fiber filters on top of each fritted support.
8.6 For each sample to be filtered, cut a 47 mm DM-450 filter into quarters. Place one
quarter, glossy side down, on top of the Type A/E glass fiber filter.
8.7 Position the filter funnel on top of the DM-450 filter and clamp securely in place.
8.8 Add several milliliters of technical grade isopropanol (IPA) to the funnel with a
wash bottle. Apply the vacuum and check for leakage at the base of the funnel. If leakage
occurs, unclamp and reposition funnel, then recheck for leakage. Turn off vacuum.
8.9 Place the beakers containing the dust/alcohol slurry into the ultrasonic bath for 1 to 2 minutes to disperse the dust.
8.10 Remove the beakers from the bath, wipe any excess water from the outside, then
carefully pour the slurry into the filter funnel, being careful not to lose any drops
of alcohol. Apply the vacuum.
8.11 Rinse the inside of the beaker with IPA from the wash bottle and add the rinsing
to the funnel. Repeat this rinsing a second time.
8.12 When the depth of the liquid in the funnel reaches about 2 centimeters above the
filter, gently rinse the inside of the funnel with IPA and filter until all alcohol is
removed. When the alcohol is below the 'lip' on the funnel, carefully rinse the 'lip'
on the inside of the funnel so as not to disturb the ash deposit.
8.13 When filtration is complete, remove the clamp and lift off funnel while taking
care not to scrape off or disturb the deposit on the DM-450 filter. Release the vacuum.
8.14 Remove each filter from the filter base. Number the corner of the filter with the
beaker number and place the filter in a petrislide which is numbered and lettered the same
as the beaker so that the samples are not mixed up.
8.15 Prepare a filter blank by filtering IPA through a DM-450 filter quarter as in
Sections 8.5 through 8.8. Place the blank filter in a petrislide marked "blank".
8.16 Set the petrislides containing the filters on the slide warmer with the lids
partially ajar to permit evaporation. Several holes, approximately 1 mm in diameter
drilled through the top of the petrislides ensure thorough evaporation of the alcohol.
Allow the filters to dry for about 30 minutes. Remove the petrislides from the slide
warmer and close the lids.
Note: Drying samples in this manner is necessary due to the presence of an
interfering peak, created from the combination of the alcohol, polystyrene (petrislide)
and the heat from the hotplate, which causes an error in the baseline position and the
quartz peak height measurement.
8.17 Set the instrument parameters on the FTIR as follows:
||Interleaved (requires sample shuttle accessory)
||Number of scans:
Note: When using the FTIR, the setting of these parameters and the following
sections, 8.18 through 8.20 are performed through computer programs.
8.18 Prior to scanning any set of samples or standards, check the operation of the
infrared spectrophotometer using a polystyrene film standard. Scan the polystyrene standard
between 1,000 and 850 cm-1 . An absorption band should occur at 908
cm-1 . The intensity (peak height) of the absorption band from a baseline drawn
between the shoulders on each side of the peak should be within the limits established for
the film on the particular instrument being used.
Note: this intensity and its limits vary from instrument to instrument and
between one standard film and another, and must be established by direct observation over
a period of time. If either or both of these conditions are not met, then it may indicate
that there is a problem with the spectrophotometer. No samples should be analyzed until
the problem is brought to the supervisor's attention and until corrective action is taken
as dictated by the operator's manual or repair personnel.
The polystyrene film is used as a standard and must be cared for accordingly.
Keep polystyrene films in suitable containers to prevent them from becoming dirty or scratched.
8.19 Scan all samples between frequencies of 1,000 and 700 cm-1, beginning with the three QA samples. If quartz
is present in a sample, a doublet will be present in the scanned range, the higher
frequency peak at 800 cm-1 . Kaolinite in the sample is recognizable as an
absorption band at 917 cm-1 , usually on the shoulder of a broad, more intense
band. (If both quartz and kaolinite are present in a sample, the kaolinite band in the
800 cm-1 region is obscured by the quartz doublet.) The infrared scan for a
typical field sample containing both quartz and kaolinite is shown in Figure 3.
8.19.1 Remove one filter at a time, so as not to mix samples, from its petrislide
holder and place it onto an infrared sample holder (Section 6.18). Use a light source to
center the deposit over the hole in the holder, then secure the filter with a ring magnet
8.20 Determine the results for all samples, beginning with the three QA samples. The
QA samples are a test of the total system operation: Low-temperature ashing,
the filtering process, and infrared scanning. If the QA sample results are not within
established limits, notify the laboratory supervisor. If the QA sample results are within
the QA program limits, then determine the quartz content of all samples ashed. (See
Internal Quality Assessment Program for Quartz Analysis, October 20, 1992 for an explanation
of the QA samples.)
8.19.2 Insert the holder with the filter sample into the sample position of the sample shuttle.
8.19.3 Place the dried blank filter onto a holder, secure with a ring magnet, and
insert into the reference position of the sample shuttle.
8.20.1 When not automatically performed through computer programs, determine the
peak heights for the absorption bands for each sample according to the following steps.
184.108.40.206 Draw a baseline for the quartz/kaolinite absorbance band between 815 and
8.20.2 Calculate the corrected absorbance for quartz at 800 cm-1 :
770 cm-1 .
220.127.116.11 Draw a baseline for the kaolinite absorbance band between 950 and 895 cm-1 (see Figure 3).
18.104.22.168 For each peak, draw a straight line from the vertex of the peak at either 917
or 800 cm-1 down through the baseline drawn in Sections 22.214.171.124 and 126.96.36.199.
188.8.131.52 Determine the height of each peak in absorbance units, from the peak vertices
to the point where the vertical lines intersect the baselines.
184.108.40.206 Determine the kaolinite contribution to the quartz/kaolinite peak at 800
cm-1 from the calibration data (Section 9):
|kaolinite abs.@ 800 cm-1 = kaolinite abs.@ 917 cm-1 X mean abs.@800
220.127.116.11 Subtract the kaolinite absorbance contribution to the 800 cm-1 quartz/kaolinite
peak from the total absorbance:
|corrected abs. quartz = abs. quartz + kaolinite @800 cm-1 - abs. kaol. @ 800 cm-1
8.20.3 Calculate the mass of quartz present in the samples using the calibration
information (Section 9):
8.21 To determine the percent quartz, divide the mass of quartz (micrograms) by the
sample mass (converted to micrograms) and multiply by one hundred. The precision of the
percent determination is dependent on the precision of the sample mass determination.
||mass of quartz (µg) = corrected absorbance
9.1.1 Prepare a suspension of kaolinite in IPA, 100 micrograms of kaolinite per milliliter of alcohol.
18.104.22.168 Weigh out 25.000 ±0.001 milligrams of dried kaolinite.
9.1.2 Prepare kaolinite standards using the same filtering apparatus described in
Sections 6.8, 6.9, and 6.16 and illustrated in Figure 1. Position two Type A/E glass fiber
filters and one quarter of a DM-450 filter on each fritted support as
described in Sections 8.5 and 8.6. Position and clamp the filtering funnel in place and
visually check for leaks as indicated in Sections 8.7 and 8.8 using reagent grade IPA.
22.214.171.124 Quantitatively transfer the kaolinite to a 500 milliliter volumetric flask,
adjust the temperature of the suspension to 20°C using either hot or cold water
baths as necessary, and bring to volume with reagent grade IPA.
126.96.36.199 Disperse the kaolinite by placing the flask in an ultrasonic bath for 30 minutes.
188.8.131.52 Cool the flask in a cold water bath until the temperature of the suspension returns to 20°C.
9.1.3 Prepare at least five DM-450 filters containing the following quantities of the
kaolinite standard material: 50, 100, 300, and 500 and 750 micrograms. These are obtained
by pipetting 1, 2, 6, 10, and 15 milliliters, respectively, of the standard suspension
onto the filters.
184.108.40.206 Vigorously shake the flask with the kaolinite suspension about 15 times.
9.1.4 When dry, scan the standards on the infrared spectrophotometer between the
frequencies of 1,000 and 700 cm-1 , following Sections 8.17 to 8.19.
220.127.116.11 Withdraw an aliquot of the suspension from the center of the flask with the
appropriate pipette, then allow this to drain back into the flask to condition the pipette. Repeat.
18.104.22.168 Draw the liquid up to the mark on the pipette, adjusting as necessary.
22.214.171.124 Drain the suspension into the filter funnel. Do not blow out the pipette.
126.96.36.199 Apply vacuum to the funnel and complete the preparation of the kaolinite standard
as described in Sections 8.13 to 8.16.
188.8.131.52 Complete preparation of the remaining kaolinite standards as described above.
Shake the flask three or four times before each aliquot is withdrawn.
9.1.5 Calculate the absorbance of kaolinite at 917 cm-1
and at 800 cm-1 , as described in Section 184.108.40.206
through 220.127.116.11, for each of the kaolinite standards.
9.1.6 Determine the ratio of the net absorbance at 917 cm-1 to the net
absorbance at 800 cm-1 for each sample.
9.1.7 Determine the mean ratio for the five samples. This ratio is used to determine the kaolinite
contribution to the 800 cm-1 quartz peak.
9.1.8 Calculate the absorbance per microgram of kaolinite for each of the standards.
||ex.:|| absorbance per microgram = absorbance @ 917 cm-1
9.1.9 Calculate the mean absorbance per microgram for the five standards. This value is used to
determine the mass of kaolinite in a sample.
9.2.1 Prepare a suspension of -5 micrometer MINUSIL quartz in isopropyl IPA, 10 micrograms of MINUSIL per milliliter of alcohol.
18.104.22.168 Weigh out 10.00 ±0.01 milligrams of dried -5 micrometer MINUSIL.
9.2.2 Prepare the quartz standards using the same filtering apparatus described in
Sections 6.8, 6.9, and 6.16, and Figure 1. Position two Type A/E glass fiber filters and
one quarter of a DM-450 filter on each fritted support as described in
Sections 8.6 and 8.7.
22.214.171.124 Quantitatively transfer the MINUSIL to a 1,000 ml volumetric flask, adjust the
temperature of the suspension to 20°C using either hot or cold water baths as necessary,
and bring to volume with reagent grade IPA.
126.96.36.199 Disperse the MINUSIL by placing the flask in an ultrasonic bath for 30 minutes.
188.8.131.52 Cool the flask in a cold water bath until the temperature of the suspension returns to 20°C.
9.2.3 Prepare at least five DM-450 filters containing the following quantities of the
quartz standard material: 20, 50, 100, 200, and 300 micrograms. These are obtained by
pipetting 2, 5, 10, 20, and 30 milliliters, respectively, of the standard suspension onto
the filters. Complete preparation of the standards following sections 184.108.40.206 through 9.1.4.
9.2.4 Calculate the absorbance of quartz at 800 cm-1 for each standard, as
in Section 220.127.116.11, 18.104.22.168 and 22.214.171.124.
9.2.5 Calculate the absorbance per microgram of quartz for each of the quartz standards.
9.2.6 Calculate the mean absorbance per microgram for the five quartz standards. This
value is used to determine the mass of quartz in the sample.
Anderson, C.C. Collaborative Tests of Two Methods for Determining Free Silica in
Airborne Dust. DHHS (NIOSH) Publication No. 83-124, Contract No.
210-79-0059, February 1983.
Freedman, R.W., S.Z. Toma, and H.W. Lang. On Filter Analysis of Quartz in Respirable
Coal Dust by Infrared Absorption and X-ray Diffraction. Am. Ind. Hyg.
Assoc. J., v. 35, 1974, p. 411.
Talvitie, N. A. Determination of Quartz in Presence of Silicates Using Phosphoric
Acid. Analytical Chemistry, v. 23, No. 4, April 1951, pp. 623-626.
Talvitie, N. A., and F. Hyslop. Colorimetric Determination of Siliceous Atmospheric Contaminants.
Am. Ind. Hyg. Assoc. J., v. 19, No. 1, February 1958, pp. 54-58.
Toma, S. Z., and S. A. Goldberg. Direct Infrared Analysis of Alpha Quartz Deposited on Filters.
Analytical Chemistry, v. 44, February 1972, p. 431.
Figure 1. One half of the filtering manifold
Figure 2. Aluminum filtering funnel dimensions
Figure 3. FTIR spectrum of an ashed respirable coal mine dust sample
1. Silica, Crystalline in coal mine dust, by IR; NIOSH Manual of
Analytical Methods, Fourth Edition, August 15, 1994.
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