# Silica, Crystalline, by XRD (Filter Redeposition) (7500)

​SILICA, CRYSTALLINE, by XRD (filter redeposition) SiO2
MW: 60.08
7500
CAS: 14808-60-7 (quartz) RTECS: VV7330000 (quartz) 14464-46-1 (cristobalite) VV7325000 (cristobalite) 15468-32-3 (tridymite) VV7335000 (tridymite)
METHOD: 7500, Issue 4
EVALUATION: FULL
quartz (respirable) 10 mg/m3 /(%SiO2 +2); cristobalite and tridymite (respirable) ½ the above NIOSH: 0.05 mg/m3 ; carcinogen ACGIH: quartz (respirable) 0.1 mg/m3 cristobalite (respirable) 0.05 mg/m3 tridymite (respirable) 0.05 mg/m3
OSHA :
PROPERTIES:
Issue 1: 15 August 1990 Issue 4: 15 March 2003 solid; d 2.65 g/cm3 @ 0 °C; crystalline transformations: quartz to tridymite @ 867 °C; tridymite to cristobalite @ 1470 °C; "-quartz to ß-quartz @ 573 °C
SYNONYMS: free crystalline silica; silicon dioxide SAMPLING SAMPLER:
FLOW RATE:
CYCLONE + FILTER (10-mm nylon cyclone, HigginsDewell (HD) cyclone, or aluminum cyclone + 5-:m PVC membrane)
Nylon cyclone: 1.7 L/min; HD cyclone: 2.2 L/min; aluminum cyclone: 2.5 L/min
VOL-MIN: -MAX:
400 L 1000 L
SHIPMENT:
Routine
SAMPLE STABILITY:
Stable
BLANKS:
2 to 10 per set (see step 13.g.)
BULK SAMPLE:
High-volume or settled dust; to identify interferences
MEASUREMENT TECHNIQUE:
X-RAY POWDER DIFFRACTION
ANALYTE:
Crystalline SiO2
ASH:
Muffle furnace or RF plasma asher or dissolve in tetrahydrofuran
REDEPOSIT:
On 0.45-:m Ag membrane filter
XRD:
Cu target X-ray tube, graphite monochromator Optimize for intensity; 1° slit Slow step scan, 0.02°/10 sec Integrated intensity with background subtraction
CALIBRATION:
    IST SRM 1878a quartz, NIST SRM
N 1879a cristobalite, USGS 210-75-0043 tridymite suspensions in 2-propanol.
RANGE:
0.02 to 2 mg SiO2 per sample [2]
ESTIMATED LOD: 0.005 mg SiO2 per sample [2] ACCURACY PRECISION ( þ r ): RANGE STUDIED:
25 to 2500 :g/m3 [1] (800-L sample)
BIAS:
None known
OVERALL PRECISION (Ö rT ):
0.09 (50 to 200 :g) [1]
ACCURACY:
± 18%
0.08 @ 0.05 to 0.2 mg per sample [1]
APPLICABILITY: The working range is 0.025 to 2.5 mg/m3 for an 800-L air sample. INTERFERENCES: Micas, potash, feldspars, zircon, graphite, and aluminosilicates. See APPENDIX. OTHER METHODS: This is similar to the method in the Criteria Document [3] and P&CAM 259 [4] which has been collaboratively tested [1]. This method is similar, except for sample collection, to S315 [5,6]. Method P&CAM 109 [7,8,9], which incorporates an internal standard, has been dropped. XRD can distinguish the three silica polymorphs and silica interferences can be eliminated by phosphoric acid treatment. IR (methods 7602 and 7603) can also quantify quartz, cristobalite and tridymite if amorphorous silica and silicates are not present in large amounts. However sensitivity is reduced if multiple polymorphs are present and secondary peaks must be used. Crystalline silica can also be determined by visible absorption spectrophotometry (e.g., Method 7601), but polymorphs can not be distinguished. Visible absorption methods also have larger laboratory-to-laboratory variabilty than XRD and IR methods and therefore are recommended for research use only [10].
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition ​SILICA, CR YST ALLINE , by XRD: M ETH OD 7500, Issue 4, dated 1 5 Ma rch 2003 - Page 2 of 9
EQUIPMENT:
REAGENTS: 1. Silica Standards. a. Quartz* (SRMs 1878a, 2950, 2951, 2958) and Cristobalite* (SRMs 1879a, 2960, 2957), available from Standard Reference Materials Program, Rm . 204, Bldg. 202, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899; ww w.nist.gov. b. Tridymite* (210-75-0043) available from U.S. Geological Survey, Box 25046, MS 973, Denver, CO 80225. 2. 2-Propanol*, reagent grade. 3. De siccant. 4. Glue or tape for securing Ag filters to XRD holders. 5. Optional: tetrahydrofuran (THF)* (if LTA or m uffle furnace are una vailable). 6. 1.5 % parlodion solution. (Dissolve 1.5 g of parlodion* in isopentyl acetate* and dilute to 100 m L with isope ntyl acetate.) 7. Op tional (if ca lcite presen t): 25% v/v concentrated hydrochloric acid* (ACS reagent grade) in distilled water and 25-mm filters of PVC or cellulose ester with pore size of 1 :m or less.
See SPECIAL PRECAUTIONS.
1. Sam pler: a. Filter: Polyvinyl chloride (PVC) filter, 37mm , 5.0-:m pore size su ppo rted w ith back up pad in a two-piece, 37-m m cassette filter ho lder (preferably, conductive) held together by tape or cellulose shrink band. NOTE: Chec k eac h new lot of PVC filters by analyzing one or m ore by this method. For example, Gelman VM-1 filters (all lots) were found to be unacceptable because of high ash and background. If THF is used, chec k fo r com plete dissolution by dissolving a blank PVC filter and following steps 5c throu gh 8 . b. Cyclone: 10-m m nylon, H iggins-Dew ell (HD ), Alum inum (Al), or e quiva lent [11 ]. 2. Area air sampler: PVC m embrane filter, 37mm diameter, 5-:m pore size; three-piece filter cassette. 3. Sam pling pumps with flexible connecting tubing , capable of the following flow rates : nylon cyclone , 1.7 L/m in; HD cyclon e, 2.2 L/m in; A l cyclone, 2.5 L/m in; and bulk sampler, 3 L/min. 4. Silver mem brane filters, 25-mm diame ter, 0.45-µm pore size, available from Sterlitech Corp., 22027 70 th Ave S, Kent, W A 980321911; www.sterlitech.com. 5. X-ray powder diffractometer (XRD ) equipped with copp er targ et X-ray tube, gra phite m onoch rom ator, and scintillation detector. 6. Reference specimen (m ica, Arkansas stone, or oth er sta ble sta nda rd) for data normalization. 7. Low-temperature radio-frequency plasma asher (LTA) or m uffle furnace, or ultrasonic bath ($150 W ), for filter preparation. 8. Vacuu m filtration asse m bly and side-arm vacuum flask with a 25-m m filter holder. 9. Sieve, 10-:m, for wet sieving. 10. An alytic al balance (0 .00 1 m g); m agnetic stirrer with th erm ally insulate d top; ultrasonic bath or probe; volumetric pipettes and flask s; P yrex crucibles with covers (m uffle furnace); 40-m L wide-m outh or 50-m L centrifuge tubes (T HF m ethod); desiccator; reagent bottles with ground glass stoppers; drying oven; polyethylene wash bottle. 11. Explosion-resistant hot plate. 12. Teflon sheet, 0.3 to 1 mm thick.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition ​SILICA, CR YST ALLINE , by XRD: M ETH OD 7500, Issue 4, dated 1 5 Ma rch 2003 - Page 3 of 9
SPE CIAL PRECAUTIONS: Avoid inhaling silica dust [3]. THF is extremely flamm able and should be used in a fum e ho od. 2-Pro pan ol, parlodion and isope ntyl acetate are flamm able. Hydrochloric acid is corrosive and sho uld be use d in a fu m e ho od.
SAMPLING: 1. 2.
3.
Calibrate each personal sampling pump with a representative sampler in line. Sa m ple at 1.7 ± 5% L/min with nylon cyclone or 2.2 ± 5% L/m in with H D cyclone for a to tal sam ple size of 400 to 1000 L. Do not exce ed 2 m g dust loading on the filter. NOTE 1: Do not allow th e sam pler as sem bly to be inverted at any time whe n us ing a c yclone . Turning the cyclone to anything other than a horizontal orientation may deposit oversized material from the cyclone body onto the filter. NOT E 2: A single sampler/flow rate should 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 resp irable a eros ol sam pling convention . Flow rate s 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 to be optimal for this purpose. Outside of coa l mine dus t sam pling, the regulatory agencies currently use these flow rates with the Dorr-Oliver cyclone in the United States and the Higgins-Dew ell sampler in the United Kingdom. Though the sampling recomm endations presented in a NIOSH Criteria Document have been form ally accepted by MSHA for coal mine dust sampling, the Dorr-Oliver cyclone at 2.0 L/min with 1.38 conversion fa cto r is currently used in the United States for the purpose of matching an earlier sampling convention [12]. In a ny case, a single sam pler/flo w rate should be used in an y given application so as to elim inate bias introduced by differences betwe en sam pler types and sam pler convention s [11]. Take an area air sample or collect a settled dust sample, if dust in the work environment has not been previously characterized.
SAMPLE PREPARATION: 4.
5.
Sam ples may be characterized by one of the following methods, as appropriate. a. Interference check. Prepare area dust sample or settled dust bulk sample for XRD analysis by mounting the collection sample directly on an XRD sam ple holder, or by depositing or redepositing the dust on another filter for mounting, or by packing an X RD powde r holder. Proceed to step 11. b. Qualitative Analysis. Prepare the area air sample or settled dust sample for qualitative analysis by grinding and/or wet sieving to best match the airborne dust particle size. W et sieve with a 10-:m sieve, 2-p ropanol, and an ultrasonic bath [13], followed by evaporation of e xcess alcohol, drying in an oven for 2 hours, and overnight storage in a desiccator. Deposit the end product on a filter (steps 7-8) or pac k in a conven tional XRD po wder holder. NOT E 1: For quantita tive de term inatio n of % SiO 2, weigh out, in triplicate, 2 mg sieved dus t, trans fer to a 50-m L be aker, ad d 10 m L 2-p ropa nol, and co ntinue with ste p 6. NOT E 2: In a bulk sam ple, if there is an interfering compound(s) that renders the identification and qua ntitation o f qua rtz very difficult, the sam ple will need to be carefully treated in hot phosphoric acid [14] to dissolve the interfering compound(s) and avoid the loss of quartz. This treatment can be used to diss olve s everal 50-m g sa m ple aliqu ots in order to concentrate the quartz content for the purpose of lowering the LOD. Use one of the following methods to prepare filter samples and blanks: a. Low Temperature Ashing: Place the filters in 50-mL beakers within the low temperature asher so that the sam ple e xposure to the plasm a is o ptim ized. Ash accord ing to m anufa cturer's instructions. After ashing, carefully add 15 mL 2-propanol to each beaker; or b. Muffle Furnace Ashing: i. If the samples contain a significant amount of calcite (>20% of total dust loading), silica may be lost due to formation of Ca SiO 3. Remove the calcite by the following procedure: Place a 0.5-:m , 25-m m PVC filter in the filtration apparatus and clamp the filter funnel over it. Rem ove the sam ple filter from the cassette, fold, and drop it on the 25-mm filter. Add 10 mL 25% v/v HCl and
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition ​SILICA, CR YST ALLINE , by XRD: M ETH OD 7500, Issue 4, dated 1 5 Ma rch 2003 - Page 4 of 9
6.
7.
8.
5 m L 2-propanol to the filter funnel and allow to stand for 5 min. Apply vacuum and slowly asp irate the acid and alcohol in the funnel, washing with three successive 10-mL portions of distilled water. Release the vacu um . Carry both filters through the ashing step together. ii. Place the filter samples in porcelain crucibles, loosely cover and ash in muffle furnace for 2 h at 600 °C (8 00 °C if graphite is present). Ad d several m L 2-p ropanol to th e ash, sc rape the crucible with a glas s rod to loos en a ll particles and transfer the residue to a 50-mL beaker. W ash the crucible several more times and add wash to beaker. Add 2-propanol to the beaker to bring the volume to about 15 mL; or c. Filter Dissolution: Using forceps and a spatula, remove the filter from the cassette, fold the filter three times, and place in the bottom of a 40- or 50-mL centrifuge tube. Add 10 mL TH F and allow to stand for at leas t 5 m in. Cap the cen trifuge tube with alu m inum foil to prevent contamination. Gently agitate the centrifuge tube by hand or with a vortex mixer mak ing sure the THF does not go near the top of the tube. Place the tube in an ultrasonic bath (water level 2.5 cm from top) for at least 10 m in. (The filter should be totally dissolved.) Just prior to filtering, agitate the sample for 10 to 20 sec on a vortex mixer. Continue with step 6, substituting THF for 2-propanol and centrifuge tube for beak er. Cover the beaker with a watchglass and agitate in an ultrasonic ba th for a t least 3 m in. Observe the suspension to ma ke su re that the agglom erated particles are broken up. W ash the underside of the watchglass w ith 2-propanol, collecting the washings in the beak er. Place a silver filter in the filtration apparatus. Attach the funnel securely over the entire filter circumference. W ith no vacuum, pour 2 to 3 mL 2-propa nol on to the filter. Pour the sample suspension from the bea ker into the fu nne l. After the trans fer, rins e the bea ker several tim es a nd a dd rinsings to the funnel for a total volume of 20 mL. In order to minimize feathering o f the sample outside the deposition area, allow the suspension to settle for a few minutes prior to applying vacuum. Do not rinse the chimney after the material has been deposited on the silver filter. Rinsing the chimney can disturb the thin layer deposition. Leave the vacuum on after filtration to produce a dry filter. Place 2 drops of 1.5% parlodion solution on a glass slide. Remove the silver filter with forceps and fix the material to the filter by placing the bottom side of the filter in the parlodion so lution. Place the saturated filter on top of the Teflon sheet which has been heated on the hot plate at a low temperature setting. W hen thoroughly dry, mount the silver filter in the XRD sam ple holder.
CALIBRATION AND QUALITY CONTRO L: 9.
Prepare and analyze at least 6 levels of standard filters. NOT E 1: Calibration standards are limited to NIST and USGS certified standards of known purity, particle size, and sample-to-sample homogeneity. At least 12 materials, including 5-:m M inU-Sil, previously used by laboratories throughout the United States and Canada, have been evaluated, and non e ha ve been foun d to be acceptable alternatives to the certified standards cited within this method [10]. Standard reference materials should be corrected for phase purity. NOTE 2: Crystalline silica methods require calibration standards of known purity, specific particle size and distributio n, and sam ple-to-sam ple hom ogeneity. Establishing traceability of secondary calibration standards to the specified NIST and USGS primary standards requires the use of measurem ent methods with better precision and accuracy than the X RD, IR and visible absorption spectrophotometry methods comm only used in the industrial hygiene field can provide. In addition, particle 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 calibra tion se t ("-quartz) and NIST SRM 2960 calibration set (cristobalite) may be useful for preparing working standards at known concentrations. a. Prepare two suspensions of each analyte in 2-propanol by weighing 10 and 50 mg of the standard material to the nearest 0.01 m g. Quan titatively transfer each to a 1-L glass-stoppered bottle using 1.0 0 L of 2 -propanol. b. Suspend the powd er in 2-propanol with an ultrasonic probe or bath for 20 m in. Im m ediately m ove the bottle to a m agn etic stirre r with therm ally insulated top and add a stirring bar. Allow the solution to return to room tem perature before withdrawing aliquots.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition ​SILICA, CR YST ALLINE , by XRD: M ETH OD 7500, Issue 4, dated 1 5 Ma rch 2003 - Page 5 of 9 c.
10.
Mount a silver filter on the filtration apparatus. Place several m L of 2-propano l on the filter. Turn off the stirrer an d sh ake vigorous ly by hand . Imm ediately rem ove the stopper and withdraw an aliquot from the center at half-height of the 10 mg/L or 50 mg/L suspension. Do not adjust the volume in the pipet by expelling part of the suspension. If more than the desired aliquot is withdrawn, discard the aliquot in a beaker, rinse and dry the p ipet, an d tak e a new a liquot. Transfer the aliquot from the pipet to the silver filter, keeping the tip of the pipet near the surface but not submerged in the delivered suspension. d. Rinse the pipet with several mL 2-propanol, draining the rinse into the funnel. Repeat the rinse several times. e. Allow the su sp en sio n to settle for a few minutes prior to applying vacuum. Apply vacuum and rapidly filter the suspension. Do not wash down the sides of the funnel after the deposit is in place since this will rearrange the material on the silver filter. Leave vacuum on until filter is dry. Place 2 drops of 1.5% parlodion solution on a glass slide. R em ove the silver filter with forceps and fix the material to the filter by placing the bottom side o f the filter in the parlodion solution. Place the saturated filter on top of the heate d T eflon she et. W hen thoroughly dry, mount the silver filter in the XRD sam ple holder. Prepare working standard filters, in triplicate, at e.g., 10, 20, 50, 100, 250, and 500 :g. f. Analyze the working standards together with samples and blanks (step 12). The XRD intensities for the working standards (step 12.d) are designated Iox and are then n orm alized (s tep 12.e) to obtain Îox . Correct the intensities of working standards >200 :g for m atrix abso rption (step s 12 .f and 13). g. Prepare a calibration graph (Î ox , vs :g of each s tandard). NOTE: Poor repeatability (>10% above 0.04 mg silica) at any given level indicates that new standards should be made. The data should lie along a straight line. A weighted least squares (1/F 2 weighting) is preferable. h. Determine the slope, m, of the calibration graph in counts/:g. The intercept, b, on the abscissa should be within ± 5 :g of zero. NOTE: A large intercept indicates an error in determ ining the background, i.e., an incorrect baseline or interference by another phase. NOTE: The following proce dure for abso rption correction is not necessary in situations that have been previously documented as requiring no corrections. Select six silver mem brane filters as media blanks randomly from the same box of filters to be used for depositing the samples. These will be used to test for sample self-absorption. Mount each of the m edia blanks on the filtration a ppa ratus and app ly vacuu m to draw 5 to 10 m L 2-propan ol through the filter. Rem ove, let dry, and mount on XRD holders. Determine the net normalized count for the silver peak, îAg, for ea ch m edia blank (step 12.g). Ob tain an average value for the six m edia blank s, Î Aog. NOTE: The analyst is a critical part of this an alytical proced ure [1 2]. A high level of analyst expertise is required to optimize instrument parameters and correct for matrix interferences either during the sample preparation phase or the data ana lysis and interpretation pha se [15]. The analyst should have som e training (university or short course) in mineralogy or crystallography in order to have a background in crystal structure, diffraction patterns and mineral trans form ation. In addition, an inten sive short course in the fun dam entals of X -ray diffractio n can be useful.
MEASUREMENT: 11. Obta in a qualitative X-ray diffra ction scan (e.g., 10 to 80 °22) of the area air sample (or bulk settled dus t) to determine the presence of free silica polymorphs and interferences (see APPENDIX). The diffraction peaks are: Mineral Qu artz Cristoba lite Tridym ite Silver
Peak (2-Th eta Degre es) Prima ry Secon dary Tertiary 26.66 20.85 50.16 21.93 36.11 31.46 21.62 20.50 23.28 38.12 44.28 77.47
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition ​SILICA, CR YST ALLINE , by XRD: M ETH OD 7500, Issue 4, dated 1 5 Ma rch 2003 - Page 6 of 9 NOTE: The re is an alternative to scanning an area air sample, settled dust sample, or ground bulk sam ple to prove lack of contamination. A slow scan of the three main peak s of quartz (also cristobalite and tridym ite if their ab sence has not been pre viously confirm ed) on a personal air sample, with verification that their intensity ratios are within 15% of pure quartz, is sufficient evidence that other materials are not interfering in the silica determination. 12. Perform the following for each sam ple, working standard, and blank filter: a. Mount the reference spe cim en. Determ ine the net intensity, I r, of the reference specimen before and after each filter is scanned. Use a diffraction peak of high intensity that can be rapidly but reproducibly (S r <0.01) measured. b. Mount the sam ple, work ing standard, or blank filter. Measure the diffraction peak area for each silica po lymo rph. Scan times m ust be long, e.g., 15 min (longer scan times will lower the limit of detection). c. Mea sure the background on each side of the peak for one-half the time used for peak scanning. The sum of these two counts is the average background. Determine the position of the background for each sample. d. Ca lculate the net intensity, Ix, (the difference between the peak integrated count and the total back ground c ount). e. Ca lculate and reco rd the norm alized intensity, î x, for each peak:
NOTE: Select a convenient normalization scale factor, N, which is approximately equivalent to the net count for the reference specimen peak, and use this value of N for all analyses. Normalizing to the referenc e sp ecim en inte nsity compensates for long-term drift in X-ray tube inte nsity. If intensity measurem ents are stable, the reference specimen m ay be run less frequently and the net intensities should be normalized to the most recently-measured reference inten sity. f. Determine the norm alized coun t, ÎAg, of an interference-free silver peak on the sample filter following the same procedure. Use a short scan time for the silver peak (e.g., 5% of scan time for analyte peaks) throughout the method. g. Fie ld blanks may be analyzed by scanning the 2-theta range used for the analyte and silver peaks to verify that contam ination of the filters has not occu rred. The analyte peak should be absent. The normalized intens ity of the silver pea k shou ld m atch that of the m edia blank. Each laboratory sh ou ld dete rmine the specifics of field blank use for its application. W hen contamination does occur, the reason should be investigated and appropriate action taken. In practice, contamination of field blank s is extrem ely rare and usually is not consistent across filters. The analysis of blanks may be abbreviated if experience indicates that contamination is not likely with current field and laboratory operations ; how ever, occ asional co nfirm ation o f non -contam ination is pruden t.
CALCULATIONS: 13. Ca lculate the conc entra tion of crystalline silica, C (m g/m 3), in the air volume sa m pled, V (L):
îx b m f(t)
normalized intensity for sample peak intercept of calibration graph (Î ox vs. :g) slope of calibration graph, counts/:g !R ln T/(1 ! T R) = absorption correction factor (Table 1)
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition ​SILICA, CR YST ALLINE , by XRD: M ETH OD 7500, Issue 4, dated 1 5 Ma rch 2003 - Page 7 of 9 R T îAg ÎAog
sin (1 Ag)/sin (1 x) îAg/(average ÎAog) = transm ittan ce of s am ple norm alize d silver pe ak intensity fro m sam ple normalized silver peak intensity from m edia blanks (average of six values)
EVALUATION OF METHOD: This method is based on P&CAM 259 which was collaboratively tested [1]. The testing included a ruggedization step to test the effects of the use of muffle furnace or plasma asher (but not the use of TH F), shipment of samples, ashing time, and ultrasonication time. None of these factors was found to have an effect. The m ethod was shown to have no bias when referenced to the Talvitie spectrophotometric method [14] and when all standards and sam ples were M in-U-Sil 5. The relative standard de viations (S r) for intralaboratory, total measurem ent and overall (including sampling) variability are:
Analyte Level (µg)
Measurement Precision (S r)
Intralaboratory
50-200 20 10
0.08 [1] 0.20 [5] 0.28 [9]
Total (intra- and inte rlaboratory)
50-200
0.17 [1]
Overall Precision (S rT)
0.29 [1]
REFERENCES: [1] [2] [3] [4]
[5] [6] [7]
[8] [9] [10] [11]
[12] [13]
Anderson CC [9183]. Collaborative tests of two m eth ods for determ ining free silica in airborne d ust. U.S . Departm ent of He alth an d Hum an S ervices, P ubl. (N IOS H) 8 3-12 4. NIOS H [1983]. Use r check , UBT L, NIOS H Se quenc e #4121 -M (unpu blished) NIOSH [1974]. Criteria for a Recom mended Stand ard: O ccu pation al Expos ure to Crystalline Silica. U.S . Departm ent of He alth, Ed uca tion, and W elfare , Pub l. (NIO SH ) 75-120 . NIO SH [1979]. Silica, crystalline: Method P&CAM 259. In: Taylor DG, ed., NIOSH M anual of Analytical Methods, 2nd ed., Vol. 5. Cincinnati, OH: U.S. Department of Health, Education, and W elfare, Publ. (NIO SH ) 79-141 . Ibid, Vol. 3, S315. U.S. Department of Health, Education, and W elfare, Publ. (NIOSH) 77-157-C (1977). NIOSH [1977]. Documentation of the NIOSH Validation Tests. S315, U.S. Department of He alth, Educa tion, an d W elfare , Pub l. (NIO SH ) 77-185 . NIOSH [1977]. Silica (XRD): Method P&CAM 109. In: Taylor DG, ed., NIOSH Manu al of Analytical Methods, 2nd ed., Vol. 1. Cincinnati, OH: U.S. Department of He alth , Ed ucatio n, and W elfare, P ubl. (NIO SH ) 77-157 -A. Bu m ste d H E [1 973]. D ete rm ination of a lpha-quartz in the res pirable portion of airborne particles by Xray diffraction. Am Ind Hyg Assoc J 34:150 . Peters ET [1976]. Evaluation of the NIOSH X-ray diffraction method for the determination of free silica in respirable dust. Final Report, NIOSH Contract CDC-99-74-51. Eller PM, Feng HA, Song RS, Key-Schwartz RJ, Esche CA, Groff JH [1999]. Proficien cy a na lytical testing (PAT) silica variability, 1990-1998. Am Ind Hyg Assoc J 60(4):533-539. Key-Sch wartz RJ, Baron P A, B artley DL, Rice FL, Schlecht PC [2003]. Chapter R, Determination of airborne crystalline silica. In: NIO SH Ma nua l of Analytical Metho ds, 4 th ed., 3 rd Suppl. Cin cinnati, OH: U.S. Departm ent of He alth and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for O ccu pation al Safety and Health, DHHS (NIOSH) Publication No. 2003-154. Inhaled Particles and Vapours [1961]. Pergamon Press, Oxford, U.K. Kupel RE , Kin ser RE, M auer PA [1968]. Se paration and analysis of the less than 10-micron fractions of industrial dusts. Am Ind Hyg Assoc J 29:364 .
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition ​SILICA, CR YST ALLINE , by XRD: M ETH OD 7500, Issue 4, dated 1 5 Ma rch 2003 - Page 8 of 9 [14] [15] [16] [17] [18]
[19] [20] [21]
Talvitie NA [1951]. Determination of q uartz in presence of silicates using phosphoric acid. Anal Chem 23 (4). Hurst VJ, Schroeder PA and Styron RW [1997]. Accurate quantification of quartz and other phases by powder X-ray diffractometry. Anal Chem Acta 337:233-252. W illiams D D [1959]. Direct quantitative diffractometric analysis. Anal Chem 31:184 1. Ab ell MT, Dollberg D D, Crable JV [1981]. Quantita tive analysis of dust samples from occupational environments using computer automated X-ray diffraction. Advances in X-Ray Analysis 24:37. Ab ell MT, Dollberg DD, Lange BA, Hornung RW , Haartz JC [1981]. Absorption corrections in X-ray diffraction dust analyses: procedures employing silver filters. Electron Microscopy and X-Ray Application s, V. 2, p. 115 , Ann Arbor Science P ublishers, Inc. Dollberg DD, Abell M T, Lange BA [1 980]. O ccupatio nal health analytic al chem istry: quantitation using x-ray powder diffraction. ACS Symposium Series, No. 120, 43. Altree-W illiams S, Lee J, Mezin NV. Qualitative X-ra y diffractometry on respirable dust collected on nuclepore filters. Ann Occup Health Hyg 20:109 . Leroux J, Po wers C [1970]. Direct X-ray diffraction quantitative analysis of quartz in industrial dust film s depos ited on silver m em brane filters. Occ up He alth Rev 21:26.
METHOD REVISED BY: Rosa Key-Schwartz, Ph.D., Dawn Ramsey, M.S., and Paul Schlecht, NIOSH/DART.
APPENDIX: INTERFERENCES Interferences include barite, micas (muscovite, biotite), potash, feldspars (m icrocline, plagioclase), montm orillonite, sillimanite, zircon, graphite, iron carbide, clinoferrosillite, wollastonite, sanidine, leucite, orthoclase, and lead sulfide. The patterns for three forms of aluminum phosphate [JCPDS 10-423, 11-500, 20-44] are practically identical to those of quartz, cristobalite and tridymite, respectively. The quartz secondary and cristobalite primary peaks are c lose; cristob alite secon dary peak is overlapped b y a qua rtz peak; tridymite, if present in sufficient quantity, will interfere with all of the main (primary, secondary and tertiary) quartz and cristobalite peaks. Silver chloride, if present on the silver filter, interferes slightly with the primary quartz peak. Many of these interferences occur in the presence of quartz; however, in a study of samples collected in 11 different industries, Altree-W illiams [20] found no significant interferences. The pre sence of ele m ents s uch as iro n can res ult in appreciable X -ray fluorescence which leads to high background intensity. A diffracted-beam m onochromator will minimize this problem. If calcite is present, loss of quartz will occur when samples are ashed in a muffle furnace. See SAMPLE PREPAR ATION (step 5.b) for procedure to remove calcite. If interferences with the primary silica peak are present, use a less sensitive peak. W hen overlaps are not severe, a sm aller receiving slit or chromium radiation may be used; however, a new calibration curve will be necessary.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition ​SILICA, CR YST ALLINE , by XRD: M ETH OD 7500, Issue 4, dated 1 5 Ma rch 2003 - Page 9 of 9 Table 1.
Absorp tion correction factor as a function of transmittance for some silica-silver peak com bination s [16-21].
Transmittance Silica T Silver 1.00 0.99 0.98 0.97 0.96 0.95 0.94 0.93 0.92 0.91 0.90 0.89 0.88 0.87 0.86 0.85 0.84 0.83 0.82 0.81 0.80 0.79 0.78 0.77 0.76 0.75 0.74 0.73 0.72 0.71 0.70 0.69 0.68 0.67 0.66 0.65 0.64 0.63 0.62 0.61 0.60 0.59 0.58 0.57 0.56 0.55 0.54 0.53 0.52 0.51 0.50
26.66 38.12 1.0000 1.0071 1.0144 1.0217 1.0292 1.0368 1.0445 1.0523 1.0602 1.0683 1.0765 1.0848 1.0933 1.1019 1.1106 1.1195 1.1286 1.1378 1.1471 1.1566 1.1663 1.1762 1.1863 1.1965 1.2069 1.2175 1.2283 1.2394 1.2506 1.2621 1.2738 1.2857 1.2979 1.3103 1.3230 1.3359 1.3491 1.3626 1.3765 1.3906 1.4050 1.4198 1.4349 1.4504 1.4662 1.4824 1.4991 1.5161 1.5336 1.5515 1.5699
f(T) (at indicated degrees 2-2) 26.66 20.83 20.83 44.28 38.12 44.28 1.0000 1.0000 1.0000 1.0082 1.0091 1.0105 1.0166 1.0184 1.0212 1.0251 1.0278 1.0321 1.0337 1.0373 1.0432 1.0425 1.0470 1.0544 1.0514 1.0569 1.0659 1.0605 1.0670 1.0776 1.0697 1.0772 1.0894 1.0791 1.0876 1.1015 1.0886 1.0982 1.1138 1.0983 1.1089 1.1264 1.1081 1.1199 1.1392 1.1181 1.1311 1.1522 1.1283 1.1424 1.1654 1.1387 1.1540 1.1790 1.1493 1.1657 1.1927 1.1600 1.1777 1.2068 1.1709 1.1899 1.2211 1.1821 1.2024 1.2357 1.1934 1.2150 1.2506 1.2050 1.2280 1.2658 1.2168 1.2411 1.2812 1.2288 1.2546 1.2971 1.2410 1.2683 1.3132 1.2535 1.2822 1.3297 1.2662 1.2965 1.3456 1.2792 1.3110 1.3637 1.2924 1.3259 1.3812 1.3059 1.3410 1.3991 1.3197 1.3565 1.4174 1.3337 1.3723 1.4362 1.3481 1.3885 1.4553 1.3682 1.4050 1.4749 1.3777 1.4218 1.4949 1.3931 1.4390 1.5154 1.4087 1.4567 1.5363 1.4247 1.4747 1.5578 1.4411 1.4931 1.5797 1.4578 1.5120 1.6022 1.4749 1.5314 1.6252 1.4925 1.5511 1.6488 1.5104 1.5714 1.6730 1.5288 1.5922 1.6978 1.5476 1.6135 1.7233 1.5670 1.6353 1.7494 1.6858 1.6577 1.7762 1.6071 1.6807 1.8037 1.6279 1.7043 1.8319 1.6493 1.7285 1.8609 1.6713 1.7534 1.8908
21.93 38.12 1.0000 1.0087 1.0174 1.0264 1.0355 1.0447 1.0541 1.0636 1.0733 1.0831 1.0932 1.1034 1.1137 1.1243 1.1350 1.1460 1.1571 1.1685 1.1800 1.1918 1.2038 1.2160 1.2284 1.2411 1.2540 1.2672 1.2806 1.2944 1.3084 1.3226 1.3372 1.3521 1.3673 1.3829 1.3987 1.4150 1.4316 1.4485 1.4659 1.4836 1.5018 1.5204 1.5394 1.5590 1.5790 1.5995 1.6205 1.6421 1.6642 1.6870 1.7103
21.93 44.28 1.0000 1.0100 1.0201 1.0305 1.0410 1.0517 1.0625 1.0736 1.0849 1.0963 1.1080 1.1199 1.1320 1.1443 1.1568 1.1696 1.1827 1.1959 1.2095 1.2232 1.2373 1.2516 1.2663 1.2812 1.2964 1.3119 1.3278 1.3440 1.3605 1.3774 1.3946 1.4122 1.4303 1.4487 1.4675 1.4868 1.5064 1.5266 1.5472 1.5684 1.5900 1.6122 1.6349 1.6582 1.6820 1.7065 1.7317 1.7575 1.7840 1.8112 1.8391
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
21.62 38.12 1.0000 1.0088 1.0177 1.0268 1.0360 1.0453 1.0548 1.0645 1.0743 1.0844 1.0945 1.1049 1.1154 1.1261 1.1370 1.1481 1.1595 1.1710 1.1827 1.1946 1.2068 1.2192 1.2319 1.2447 1.2579 1.2713 1.2849 1.2989 1.3131 1.3276 1.3424 1.3576 1.3730 1.3888 1.4050 1.4215 1.4383 1.4556 1.4732 1.4913 1.5098 1.5287 1.5481 1.5679 1.5883 1.6092 1.6306 1.6525 1.6751 1.6982 1.7220
21.62 44.28 1.0000 1.0101 1.0204 1.0309 1.0416 1.0524 1.0635 1.0747 1.0861 1.0977 1.1096 1.1216 1.1339 1.1464 1.1592 1.1722 1.1854 1.1989 1.2126 1.2266 1.2409 1.2555 1.2703 1.2855 1.3009 1.3167 1.3328 1.3493 1.3661 1.3883 1.4008 1.4187 1.4370 1.4558 1.4749 1.4945 1.5145 1.5350 1.5560 1.5775 1.5995 1.6221 1.6452 1.6689 1.6932 1.7181 1.7437 1.7699 1.7969 1.8246 1.8531