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QUARTZ
ANALYTICAL METHOD (P-7)
INFRARED DETERMINATION OF QUARTZ
IN RESPIRABLE COAL MINE DUST
| ANALYTE: |
Quartz |
METHOD NO.: |
P-7 |
| MATRIX: |
Respirable Coal Mine Dust |
RANGE: |
25-250 micrograms of quartz |
| PROCEDURE: |
Infrared |
PRECISION: |
5-10% RSD |
| DATE ISSUED: |
August 3, 1989 |
QUANTIFICATION LIMIT: |
10 µg |
| DATE REVISED: |
November 14, 1994 |
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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.
1.2 After collection, the filter capsules are reweighed to one hundredth of a milligram
in order to determine the net sample mass.
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 calibration samples.)
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 kaolinite
content.
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 RANGE AND LIMIT OF DETECTION
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 INTERFERENCES
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.
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 PRECISION AND ACCURACY
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)
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 ADVANTAGES AND DISADVANTAGES OF THE METHOD
5.1 Advantages
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
X-ray diffraction.
5.2 Disadvantages
The method requires the low-temperature ashing and redeposition of all samples prior to
analysis.
6 APPARATUS
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
illustrated.)
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 MATERIALS
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 PROCEDURE
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 the beaker.
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:
| Resolution: |
8 cm-1 |
| Acquire mode: |
Interleaved (requires sample shuttle accessory) |
| Apodization: |
Normal |
| Number of scans: |
1 |
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.
8.19.2 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 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.)
8.20.1 When not automatically performed through computer programs, determine the peak
heights for the absorption bands for each sample according to the following steps.
8.20.1.1 Draw a baseline for the quartz/kaolinite absorbance band between 815 and
770 cm-1.
8.20.1.2 Draw a baseline for the kaolinite absorbance band between 950 and 895 cm-1
(see Figure 3).
8.20.1.3 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 8.20.1.1 and 8.20.1.2.
8.20.1.4 Determine the height of each peak in absorbance units, from the peak vertices
to the point where the vertical lines intersect the baselines.
8.20.2 Calculate the corrected absorbance for quartz at 800 cm-1:
8.20.2.1 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 |
| abs.@917 |
8.20.2.2 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):
| mass of quartz (µg) = corrected absorbance |
| mean abs./microgram |
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.
9 CALIBRATION
9.1 Kaolinite
9.1.1 Prepare a suspension of kaolinite in IPA, 100 micrograms of kaolinite per
milliliter of alcohol.
9.1.1.1 Weigh out 25.000 ±0.001 milligrams of dried kaolinite.
9.1.1.2 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.
9.1.1.3 Disperse the kaolinite by placing the flask in an ultrasonic bath for
30 minutes.
9.1.1.4 Cool the flask in a cold water bath until the temperature of the suspension
returns to 20°C.
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.
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.
9.1.3.1 Vigorously shake the flask with the kaolinite suspension about 15 times.
9.1.3.2 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.
9.1.3.3 Draw the liquid up to the mark on the pipette, adjusting as necessary.
9.1.3.4 Drain the suspension into the filter funnel. Do not blow out the
pipette.
9.1.3.5 Apply vacuum to the funnel and complete the preparation of the kaolinite
standard as described in Sections 8.13 to 8.16.
9.1.3.6 Complete preparation of the remaining kaolinite standards as described above.
Shake the flask three or four times before each aliquot is withdrawn.
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.
9.1.5 Calculate the absorbance of kaolinite at 917 cm-1 and at 800 cm-1,
as described in Section 8.20.1.1 through 8.20.1.4, 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 |
| mass, µg
|
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 Quartz
9.2.1 Prepare a suspension of -5 micrometer MINUSIL quartz in isopropyl IPA,
10 micrograms of MINUSIL per milliliter of alcohol.
9.2.1.1 Weigh out 10.00 ±0.01 milligrams of dried -5 micrometer MINUSIL.
9.2.1.2 Quantitatively transfer the MINUSIL to a 1,000 ml volumetric flask, adjust the
temperature of the suspension to 20C using either hot or cold water baths as necessary,
and bring to volume with reagent grade IPA.
9.2.1.3 Disperse the MINUSIL by placing the flask in an ultrasonic bath for 30 minutes.
9.2.1.4 Cool the flask in a cold water bath until the temperature of the suspension
returns to 20C.
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.
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 9.1.3.1 through
9.1.4.
9.2.4 Calculate the absorbance of quartz at 800 cm-1 for each standard, as
in Section 8.20.1.1, 8.20.1.3 and 8.20.1.4.
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.
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| BIBLIOGRAPHY |
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.
(Return to text)
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