Quartz in Coal Mine Dust, by IR (Redeposition) (7603)
QUARTZ in coal mine dust, by IR (redeposition) SiO2
MW: 60.08
METHOD: 7603, Issue 3
CAS: 14808-60-7
RTECS: VV7330000
EVALUATION: UNRATED
OSHA : quartz (respirable): 10 mg/m3 / (%SiO2 + 2) NIOSH: 0.05 mg/m3 (suspect carcinogen) ACGIH: 0.1 mg/m3
PROPERTIES:
7603
Issue 1: 15 May 1989 Issue 3: 15 March 2003
solid; d 2.65 g/cm3 ; crystalline transformations: quartz to tridymite @ 867 °C: trydymite to crystobalite @ 1470 °C; "quartz to $-quartz @ 573 °C
SYNONYMS: free crystalline silica; silicon dioxide SAMPLING SAMPLER:
CYCLONE + PREWEIGHED FILTER (10-mm cyclone, nylon or Higgins-Dewell (HD), and PVC filter, 37-mm, 5-µm)
- see sampling section
FLOW RATE: HD cyclone: 2.2 L/min nylon cyclone: 1.7 L/min VOL-MIN: -MAX:
300 L @ 0.1 mg/m3 1000 L
SHIPMENT:
Routine
MEASUREMENT TECHNIQUE:
INFRARED ABSORPTION SPECTROPHOTOMETRY (IR)
ANALYTE:
Quartz
WEIGH:
Dust cassette
ASH:
Muffle furnace or RF plasma asher
REDEPOSIT:
0.45-µm acrylic copolymer membrane filter
IR:
Scan, 1000 to 650 cm-1 , absorbance mode with blank filter in reference beam
SAMPLE STABILITY:
Stable
BLANKS:
2 to 10 field blanks per set
CALIBRATION:
NIST SRM 1878a suspension in 2-propanol
Rrequired for OSHA standard calculations; area respirable or settled dust
RANGE:
30 to 250 µg quartz per sample [1]
ESTIMATED LOD:
10 µg quartz per sample [1]
PRECISION ( þ r ):
0.098 @ 100 to 500 µg per sample (varies with sample matrix) [1]
BULK SAMPLE:
ACCURACY RANGE STUDIED:
25 to 160 µg/sample [1] (2 mg quartz/m3 atmosphere)
BIAS:
Unknown
OVERALL PRECISION (Ö r T ): 0.13 to 0.22 (varies with sample loading and matrix ACCURACY:
±25.6 to 43.4%
APPLICABILITY: The working range is 0.03 to 0.25 mg/m3 for a 1000-L sample. The method was specifically developed for respirable coal mine dust samples [1]. The precisions (þr & þrT ) stated above are based on ruggedization data [2]. IR is useful for a simple matrix like coal dust where the interference can be removed. See also discussion of crystalline silica in Chapter R of this volume [3]. INTERFERENCES: Calcite is used as a dusting agent in coal mines and interferes by reacting with quartz during muffle furnace treatment resulting in low quartz assay. Kaolinite is sometimes present in coal dust and interferes by absorbing radiation at the quartz analytical wavelength of 800 cm-1 . These interferences are corrected by procedures given in this method. Muscovite does not interfere. Cristobalite and tridymite have absorbance peaks at 800 cm-1 . Cristobalite and tridymite have not been detected in coal mine dust. OTHER METHODS: This is similar to MSHA P-7 which was collaboratively tested [2,4]. Quartz can also be determined by Methods 7500 (XRD) and 7602 (IR). XRD can distinguish the three silica polymorphs and silica interferences can be eliminated by phosphoric acid treatment. Crystalline silica can also be determined by visible absorption spectrophotometry (e.g., Method 7601), but polymorphs cannot be distinguished. Visible absorption methods also have larger laboratory-to-laboratory variability than XRD and IR methods and therefore are recommended for research use only [5].
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition QUARTZ in coal mine dust: METHOD 7603, Issue 3, dated 15 March 2003 - Page 2 of 7 EQUIPMENT:
REAGENTS: 1. Qua rtz* (SRM 1878a, 295 0, 2951, 2958), available from Sta ndard R eference Mate rials Program, Rm. 204, Bldg. 202, National Ins titute of Stan dards T echnology, Gaithersbu rg, MD 2 0899; ww w.nist.gov. 2. 2-Propanol*, reagent grade. 3. Ca libration s tock solution, 15 µg/m L. Suspend 7.5 mg of quartz in 2-propanol in a 500-mL volumetric flask and dilute the suspension to the mark with 2-propanol (See CAL IBRAT ION A ND QU ALITY C ON TR OL). 4. Kaolinite (Hydrite UF from Geo rgia Kaolin), for standard samples, 100 µg/mL. Suspend 50 m g of dried kaolinite in a 500-m L volum etric flas k w ith 2-propa nol an d dilute the susp ens ion to the m ark with 2-prop ano l. NOTE: This is not required if muffle furnace is used to ash sam ples (see step 5). 5. Hydroch loric ac id solution*. 25% v/v conc. HCl in distilled wate r. Required if ca lcite is present and sam ples are ashed with a m uffle furnace. 6. Desicca nt (Drierite). 7. Oxygen, purified.
- See SPECIAL PRECAUTIONS
1. Sam pler: a. Filter: 37-mm diameter, 5.0-µm pore size, polyvinyl chloride filter s upp orted with back up pad in a two-piece, 37-m m cassette filter ho lder (preferably, conductive) held together by tape or cellulose shrink band. b. Cyclone: 10-m m nylon or Higgins-Dew ell (HD ). c. Sam pling head holder: Holder must keep the cassette, cyclone and coupler together rigidly so that air enters only at the cyclone inlet. 2. Area air sampler: PVC m embrane filter, 37mm , 5-µm pore size in two-piece filter cassette . Sa m ple closed fa ce at 3 L/m in 3. Sam pling pumps for: HD cyclone, 2.2 L/min; nylon cyclone , 1.7 L/m in; and area sam pler, 3 L/min. 4. Filters for standards and redeposition, 47m m diam ete r, 0.45 -µm pore size , vinyl chloride-acrylonitrile copolymer m embrane (DM -450 G elma n Science s, or equivalent). 5. Glass fiber filters, 25-mm diameter, for backup during filtration. 6. Filtratio n apparatu s for red epositing sam ple after ashing, consisting of fritted support (Millipore XX1002502), side-arm vacuum flask and sp ecial funnel similar to Millipore XX1002514 but with an internal diameter of 1.0 cm . The fun nel is glass with a b akelite bas e an d sh ould sea l to the fritted sup port to m ake the fit liquid-tight.** 7. Funne l for treating filters to rem ove calcite (required only if using a m uffle furnace): Millipore XX1002514 with apparatus in item 6 above except with funnel internal diameter ca. 1.6 cm; 0.5-µm pore size PVC filters, 37m m diam eter to recollect residue .** 8. Doub le-beam infrared spectrophotom eter, with sam ple ho lders for infra red instrum ent: metal (preferably steel) plates with a center hole to m atc h the diam ete r of the sam ple dep osit (1 cm ), and sm all ring m agn ets to hold the filter in position on the plate. 9. Low-temperature radio frequency asher (LTA ) or m uffle furnace (600 °C ). 10. Ultrasonic bath. 11. Porc elain cruc ibles with cove rs, 10-m L.** 12. Bea kers , 50-m L.** 13. Analytical balance, 0.01-mg; desiccator cab inet. 14. Magnetic stirrer with thermally insulated top,
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition QUARTZ in coal mine dust: METHOD 7603, Issue 3, dated 15 March 2003 - Page 3 of 7 EQ UIPM ENT : - cont. and stirring bars. 15. Reagent bottles with ground glass stoppers, 500-m L, and vo lum etric flasks , 500-m L.** 16. Tweezers. 17. Petri dishes, plastic, for 47-mm diameter filters. 18. Polyethylene wash bottles; metal spatulas. 19. Serological pipets, various sizes as required. 20. Lighted viewing box (optional).
Glassware should be detergent-washed, rinsed thoroughly with distilled or deionized water, and then with 2-propanol, and dried in a dust-free area.
SPECIAL PRECAUTIONS: Avoid inhaling quartz dust [6]. 2-Propanol is flam m able. H ydrochloric acid is corrosive and should be handled in a fume hood. SAMPLING: 1. Calibrate each personal sampling pump with a representative sampler in line. 2. Preweigh each filter to the nearest 0.01 mg. 3. Sa m ple at 1.7 ± 5% L/min with nylon cyclone or 2.2 ± 5% L/m in with HD cyclone fo r a tota l sam ple volum e of 300 to 1000 L. Do not exce ed 2 m g dust loading on the filter. NOT E 1: Do not allow the sampler assembly to be inverted at any time whe n using a cyclone. Turning the cyclone to anything other than a horizontal orientation may deposit oversized m aterial from the cyclone body onto the filter. NOT E 2: A single sampler/flow rate s ho uld be used for a given application. Sampling for both crystalline silica and coal mine dust should be done in accordance with the ISO/CEN/ACGIH/ASTM respirable aerosol sampling convention. Flow rates of 1 .7 L/m in for the Dorr-Oliver nylon cyclone and 2.2 L/min for the Higgins-Dewell cyclone have been found optim al for this purpose . Outside of coal m ine dust sam pling, the regulatory agencies currently use these flow rates with the Do rr-Oliver cyclone in the United States and the Higgins-Dewell sampler in the United Kingdom. Though the sampling recomm endations presented in a NIOSH Criteria Document have been formally accepted by MSHA for coal mine dust sampling, the Dorr-Oliver cyclone at 2.0 L/min with 1.38 conversion factor is currently used in the United States for the purpose of matching an earlier sampling con vention [7]. In any case, a single sam pler/flo w rate should be used in any given application so as to eliminate bias introduced by differences between sampler types and sam pler convention s [3].
SAMPLE PREPARATION: 4. 5.
Reweigh the filters under conditions identical to those before preweighing. The difference is the sam ple weight, W s (µg). Ash sample and blank filters by one of the following methods: a. Low-temperature ashing. Using forceps , trans fer filter to a 50-mL beaker. Ash 2 h at 300 watts RF power and oxygen flow rate of 75 m L/m in fo llowing tec hniques rec om m ended in the instrument m anual. After ashing, add 15 m L 2-propan ol to each beak er. b. Muffle furnace ashing. (1) If the samples contain calcite in concentrations greater than 20% of the total dust loading, wash the filters with acid using the filtration apparatus with the 1.6-cm ID glass fun nel. Place a 25-m m glas s fibe r filter over the frit area, then place a 0.5-µm , 37-mm PVC filter NIOSH Manual of Analytical Methods (NMAM), Fourth Edition QUARTZ in coal mine dust: METHOD 7603, Issue 3, dated 15 March 2003 - Page 4 of 7
6.
over the glass fiber filter. Clamp down the filter funnel. Add 5 mL 2-propanol and check for leakage. Rem ove the sample filter from the cassette. Fold it in half with the collection surface inside, then in quarters. Place the folded filter into the funnel. If necessary, push the filter to the bottom half of the funnel with a glass rod. Add 10 mL HC l solution, then 5 m L 2-propanol. Apply suction and continue until all of the liquid has been removed. Press the folded sa m ple filter on to the surface of the co llecting filter if neces sary to remove all the liquid. R em ove both filters and place in a porcelain crucible. Allow filters to air-dry. (2) If acid wash was not required, transfer filter samples and blanks to porcelain crucibles. (3) Loosely cover the crucibles and p lace in a muffle furnace. Hold for 2 h at 600 °C. After ashing, add several mL 2-propanol to the ash, scrape the crucible to loosen all particles and transfer to a 50-m L beaker. W ash the crucible several times and add wash to beaker. Add 2-propanol to the beaker to bring the volume to ca. 15 mL. Redeposit the sample residue as follows using the filtration apparatus with the 1.0-cm fun nel. W ith a slight vacuum applied, place a 25-mm glass fiber filter on the fritted base. Cut a 47-mm DM-450 filter in half. Superimpose one half over the other, glossy sides down, and place on the glass fiber filter. (The lower half of the DM-450 filter serves as a blank and is used in the reference beam of the infrared spectrometer). Position filter funnel, apply clamp and turn off vacuum. Add several mL 2propanol to the funn el. Check that the fun nel is securely and uniform ly clam ped. P lace sam ple beak ers into ultrasonic bath for at least 30 sec to ensure homogeneous dispersion. Remove a beak er, wipe exc ess wate r from the outside , trans fer slurry to the filtration funnel and reapply vacuum. During filtration, rinse the beaker twice with 2-propanol to remove all dust and add rins ings to fun nel. Co ntrol the filtration rate to ke ep the liquid near th e fun nel top during rinsing to avoid disturbing the dep osit. W hen the depth of liqu id in the funnel reaches ca. 4 cm above the filter, gently rinse the inside of funnel with 2-propanol and com plete filtration . Rem ove the clam p and lift off the fu nnel, taking care not to d istu rb and deposit. Release the vacuum . Define the deposit area by marking around the circumference using a pencil or scriber. This is especially important for standards or lightcolored sam ples. P lace the D M-450 filter ha lves in petri dishes and allow to air-dry.
CALIBRATION AND QUALITY CONTRO L: 7.
Prepare and analyze NIST SRM 1878a standard quartz filters. NOT E 1: Ca libration s tand ards are lim ited to NIST and U SG S c ertified stan dards of known purity, particle size, and sam ple-to -sample homogeneity. At least 12 materials, including 5 µm Min-U-Sil, previously used by laboratories throughout the United States and Canada, have been evaluated, and none has been fo und to be an accepta ble alternative to the certified standards cited within this method [3]. Standard reference materials should be corrected for ph ase purity. NOT E 2: Establishing traceability of secondary calibration standards to the specified NIST and USGS primary standards requires the use of measurement methods with better precision and accuracy than the XRD, IR and visible absorption spectrophotometry methods com m only used in the industrial hygiene field can provide. In addition, pa rticle size distribution measurem ents have considerable error. Therefore, the use of second ary calibration standards that are traceable to NIST and USGS certified standards is not appropriate. NOTE 3: NIST SRM 2950 calibration set ("-quartz) may be useful for preparing working standards at known concentrations. a. Place the flask containing the calibration stock solution in an ultrasonic bath for 30 to 45 min. b. Move the flask to a magnetic stirrer and stir slowly while the flask cools to room tem perature. Continue to stir slowly while preparing standards. c. Mount a DM-450 filter in the filtration apparatus in the same m anner used to redeposit the samples. Add 5 m L 2-propanol to th e fu nnel. W ithdraw an aliquot of the quartz suspension from the cente r of the flask . Draw liquid to the mark but do not attempt to adjust volume by draining pipet. Carefully wipe the outside of the pipet, then drain the suspension into th e filter fun nel. Rins e do wn th e inside wa ll of the pipet with a few m L of 2 -propan ol, draining the was hings into the filter funnel. Apply vacuum to complete the filtration. Prepare quartz standards to cover the range 10 to 25 0 µg per filter. d. Carry an additional set of these standards and media blanks through steps 5 and 6 to monitor for contamination and losses. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition QUARTZ in coal mine dust: METHOD 7603, Issue 3, dated 15 March 2003 - Page 5 of 7 NOTE:
8.
9.
Accuracy depends on obtaining uniform deposition of samples and standards across the filter surface and obtaining re prod ucible aliquo ts from the quartz s usp ens ion. This requires som e skill. The quartz calibration curve should be prepared before analyzing samples as a check on the analyst's ability to prepare uniform deposits. Repeatability should be <10% on re plicate standard s with m ore than 4 0 µg qua rtz. Perform an IR scan for each standard filter using the other half of the filter in the reference beam (steps 10 through 12). Construct a calibration graph (absorbance at 800 cm ! 1 vs. µg quartz per filter). This graph should be linear and pass through the origin. (O nly for samples ashed in LTA). Prepare suspensions of at least 5 kaolinite standards in the range 100 to 600 µg per filter. P erform an IR sca n of the kaolinite s tand ards from 100 0 to 650 cm ! 1. Draw baselines as described in step 12 and measure the height of the absorbance bands at both 915 and 800 cm ! 1. Prepare a graph with absorbance at 915 cm ! 1 as ordinate vs. absorbance at 800 cm ! 1 as abscissa. Plot a point for eac h standa rd. If possible, generate the correction curve data on the same day that coal mine dust samples are analyzed since curve param eters may vary somewhat from day to day. A curve through the points should be linear but will not pass through the origin since the peak at 915 cm ! 1 is more intense than the peak at 800 cm ! 1 and sm all am oun ts of kaolinite do not interfere with the quartz analysis. NOTE 1: Ka olinite correctio n calibration curve is required when s am ples are ashed in an LTA since kaolinite is not destroyed under these circum stances a nd has a s interfering peak at 800 cm ! 1 for which a correction must be performed. NOT E 2: A more detailed discussion of IR peaks is given in the IR sec tion of Ch apte r R of this volum e [3]. NOT E 3: S om e training (university or short course) in geology or mineralogy can be useful for the analyst and /or labo ratory mana gem ent. Althoug h m ost analytical chem ists are fam iliar with the IR tec hnique a s ap plied to organic analyses, mineralogical samples require additional knowledge of g eology and m ineralogy to correctly interpret c rystal structu re, m atrix interfe renc es a nd m ineral transform ation for the laboratory client.
MEASUREMENT: 10. 11.
12.
13.
Set appropriate instrument conditions for quantitative analysis. Place the dry D M-450 filter-half conta ining the dust deposit on a holder. Center the deposit over the hole in the holder and secure the filter with a magnet. (A lighted viewing bo x fac ilitate s th is procedure). Insert the sample into the beam of the spectrophotometer. Place the other half of the DM-450 filter on another holder, secure with a magnet and insert it into the reference beam. NOTE: For the best precision, the referenc e filter should be half of the same DM -450 filter which contains the redeposit. However, for routine analysis, the same 2-propanol-treated blank can be used for all filters with the sam e lot numb er. Run an infrared scan, in linear absorbance mode from 1000 to 650 cm ! 1. Draw an app ropriate baseline under the absorbance band at 800 cm ! 1 from ca. 820 to 670 cm ! 1. Measure and record the absorbance at 800 cm ! 1, baseline to maximum . If the sample was ashed in an LTA, the presence of ka olinite will be indicated by an absorption band with a maximum at 915 cm ! 1. Draw a baseline under this band from ca. 960 ! 1 to 860 cm ! 1. Measure and record the absorbance at 915 cm ! 1, baseline to maximum . Analyze blanks. Check results for contamination.
CALCULATIONS: 14.
Correct for kaolinite, if required. Using the sample absorbance at 915 cm ! 1, refer to the kaolinite curve to find the absorbance at 800 cm ! 1 due to ka olinite. Subtract this am ount from the sam ple absorbance at 800 cm ! 1. Use this corrected value to calculate µg quartz in the sample.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition QUARTZ in coal mine dust: METHOD 7603, Issue 3, dated 15 March 2003 - Page 6 of 7 15.
16.
If correction for kaolinite is not required, use the absorbance at 800 cm ! 1 determined in step 12. Determine the weight of qu artz, W q (µg), from the quartz standard curve. Since the deposition area for samples and standards is the same, it is not necessary to correct for area. Ca lculate the percent quartz by dividing the weight of quartz, W q (µg), by the total sam ple weight, W s (µg).
EVALUATION OF METHOD: This method is based MSHA P-7 which was collaboratively tested [2,4]. The testing included a ruggedization step to test the effects of the use of muffle furnace or plasma asher, amount of calcite or kaolinite on the sample, ashing time, pH of solvent to remove calcite, shipment of samples and others. None of these factors was found to have an effect. Results obtained by this method are equivalent to those obtained by Method 7500. A collaborative study of the rugge dized m etho d wa s pe rform ed w ith 15 lab orato ries participa ting [2]. The total erro rs an d interlabora tory and intralabora tory errors were found to be dependent on the types of samples. For samples collected from laboratory-generated aerosols, using a set of matched-flow orifices, the lower and upper limits of the relative standard deviation over the range 60 to 150 µg quartz were:
Total error (RSD) Intralaboratory error Interlaboratory error
Lower
Upper
0.13 0.07 0.08
0.22 0.10 0.14
The lower limit applies to samples containing up to 1 mg coal mine dust with less than 2% kaolinite; the upper lim it was found for samples with 2 mg coal mine dust or a lower amount of coal mine dust with more than a few percent ka olinite. The total error increased to 0.36 to 0.40 (lower and upper range) when personal sampling pumps were used to collect the sam ples. The pum p error increased the interlaboratory error. Precision for pure quartz samples is ca. 0.05 in the 100 to 500 µg ra nge [4]. Precision fo r ac tua l sam ples is not as good and depends on sample size and ashing technique. This method is particle size dependent. The particle sizes of the standards and samples should be matched as closely as poss ible to prevent a bias in the res ults , wh ich is not c orrecta ble with this m etho d. A thorough study of the range of biases has not been done for IR methods.
REFERENCES: [1] [2]
[3]
[4]
Freedman RW , Toma SZ, Lang HW [19 74 ]. On -filter an alys is of q ua rtz in respirable coal dust by infrared absorption and X -ray diffraction. Am Ind H yg Assoc J 35:411. An de rso n C C [19 83 ]. Collaborative tests of two me thods for determining free silica in airborne du st. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Ce nters for Disease Con tro l, Na tiona l Institute for O ccu pa tiona l Sa fety a nd He alth, D H H S (NIOSH) Pub. No. 83-124. Key-Sch wartz RJ, Baron PA, Bartley DL, Rice FL, Schlecht PC [2003]. Chapter R, Determination of airborne crystalline silica. In: N IOS H M anu al of Analytical M etho ds, 4 th ed., 3 rd Suppl. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2003-154. MSHA [1994]. Infrared dete rm ination of q uartz in res pirable coal mine dust: Method P-7. Pittsburgh, PA: U.S. Department of Labor, Mine Safety and Health Administration.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition QUARTZ in coal mine dust: METHOD 7603, Issue 3, dated 15 March 2003 - Page 7 of 7 [5] [6] [7]
Eller PM, Feng HA, Song RS, Key-Schwartz RJ, Esche CA, Groff, JH [1999]. Proficiency analytical testing (PAT) silica variability , 1990-1998. Am Ind Hyg Assoc J 60(4):533-539. NIOSH [1974]. Criteria for a Rec om m ended S tandard: Oc cupational Expos ure to Crystalline Silica. Cincinnati, OH: U.S. Department of Health, Education, and W elfare, Publ. (NIOSH) 75-120. Inhaled Particles and Vapours [1961]. Pergamon Press, Oxford, U.K.
METHOD REVISED BY: Paul Schlecht, Ro sa K ey-Sc hwa rtz, Ph.D ., NIO SH /DA RT .
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition