SILICA, CRYSTALLINE, by XRD (filter redeposition) 7500

1 NIOSH Manual of Analytical Methods (NMAM), Fourth Edition SILICA, CRYSTALLINE, by XRD (filter redeposition) 7500 SiO2 MW: 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: FULLI ssue 1: 15 August 1990 Issue 4: 15 March 2003 OSHA :quartz (respirable) 10 mg/m3/(%SiO2+2);cristobalite and tridymite (respirable) the mg/m3; carcinogenACGIH:quartz (respirable) mg/m3cristobalite (respirable) mg/m3tridymite (respirable) mg/m3 PROPERTIES:solid; d g/cm3 @ 0 C; crystallinetransformations: quartz to tridymite@ 867 C; tridymite to cristobalite@ 1470 C; "-quartz to -quartz@ 573 CSYNONYMS:free crystalline silica; silicon dioxideSAMPLINGMEASUREMENTSAMPLER:CYCLON E + FILTER(10-mm nylon cyclone, Higgins-Dewell (HD) cyclone, or aluminumcyclone + 5-:m PVC membrane)*see sampling sectionFLOW RATE:Nylon cyclone: L/min;HD cyclone: L/min;aluminum cyclone: L/minVOL-MIN:400 L -MAX:1000 LSHIPMENT:RoutineSAMPLE STABILITY:StableBLANKS:2 to 10 per set (see step )BULK SAMPLE:High-volume or settled dust ; toidentify interferencesTECHNIQUE:X-RAY POWDER DIFFRACTION ANALYTE:Crystalline SiO2 ASH:Muffle furnace or RF plasma asher or dissolve in tetrahydrofuranREDEPOSIT:On :m Ag membrane filterXRD:Cu target X-ray tube, graphite monochromatorOptimize for intensity.

2 1 slitSlow step scan, /10 secIntegrated intensity with backgroundsubtractionCALIBRATION::NIST SRM 1878a quartz, NIST SRM1879a cristobalite, USGS 210-75-0043tridymite suspensions in to 2 mg SiO2 per sample [2]ESTIMATED mg SiO2 per sample [2]PRECISION ( r) @ to mg per sample [1]ACCURACYRANGE STUDIED:25 to 2500 :g/m3 [1](800-L sample)BIAS:None knownOVERALL PRECISION ( rT) (50 to 200 :g) [1]ACCURACY: 18% APPLICABILITY: The working range is to mg/m3 for an 800-L air : Micas, potash, feldspars, zircon, graphite, and aluminosilicates. See METHODS: This is similar to the method in the Criteria Document [3] and P&CAM 259 [4] which has been collaborativelytested [1]. This method is similar, except for sample collection, to S315 [5,6]. Method P&CAM 109 [7,8,9], which incorporates aninternal standard, has been dropped.

3 XRD can distinguish the three silica polymorphs and silica interferences can be eliminatedby phosphoric acid treatment. IR (methods 7602 and 7603) can also quantify quartz, cristobalite and tridymite if amorphorous silicaand silicates are not present in large amounts. However sensitivity is reduced if multiple polymorphs are present and secondarypeaks must be used. Crystalline silica can also be determined by visible absorption spectrophotometry ( , Method 7601), butpolymorphs can not be distinguished. Visible absorption methods also have larger laboratory-to-laboratory variabilty than XRD andIR methods and therefore are recommended for research use only [10].SILICA, CRYSTALLINE, by XRD: METHOD 7500 , Issue 4, dated 15 March 2003 - Page 2 of 9 NIOSH Manual of Analytical Methods (NMAM), Fourth * (SRMs 1878a, 2950, 2951, 2958)and Cristobalite* (SRMs 1879a, 2960,2957), available from Standard ReferenceMaterials Program, Rm.

4 204, Bldg. 202,National Institute of Standards andTechnology (NIST), Gaithersburg, MD20899; * (210-75-0043) available Geological Survey, Box 25046, MS973, Denver, CO *, reagent or tape for securing Ag filters to : tetrahydrofuran (THF)* (if LTA ormuffle furnace are unavailable). % parlodion solution. (Dissolve g ofparlodion* in isopentyl acetate* and dilute to100 mL with isopentyl acetate.) (if calcite present): 25% v/vconcentrated hydrochloric acid* (ACS reagent grade) in distilled water and 25-mm filters of PVC or cellulose esterwith pore size of 1 :m or less.*See SPECIAL : : Polyvinyl chloride (PVC) filter, 37-mm, :m pore size supported withbackup pad in a two-piece, 37-mmcassette filter holder (preferably,conductive) held together by tape orcellulose shrink :Check each new lot of PVC filtersby analyzing one or more by thismethod.

5 For example, GelmanVM-1 filters (all lots) were foundto be unacceptable because ofhigh ash and background. If THFis used, check for completedissolution by dissolving a blankPVC filter and following steps 5cthrough 8. : 10-mm nylon, Higgins-Dewell(HD), Aluminum (Al), or equivalent [11]. air sampler: PVC membrane filter, 37-mm diameter, 5-:m pore size; three-piecefilter cassette. pumps with flexible connectingtubing, capable of the following flow rates: nylon cyclone, L/min; HD cyclone, ; Al cyclone, L/min; and bulksampler, 3 L/min. membrane filters, 25-mm diameter, m pore size, available from SterlitechCorp., 22027 70th Ave S, Kent, WA 98032-1911; powder diffractometer (XRD) equippedwith copper target X-ray tube, graphitemonochromator, and scintillation detector. specimen (mica, Arkansas stone,or other stable standard) for datanormalization.

6 Radio-frequency plasmaasher (LTA) or muffle furnace, or ultrasonicbath ($150 W), for filter preparation. filtration assembly and side-armvacuum flask with a 25-mm filter holder. , 10-:m, for wet balance ( mg); magneticstirrer with thermally insulated top; ultrasonicbath or probe; volumetric pipettes andflasks; Pyrex crucibles with covers (mufflefurnace); 40-mL wide-mouth or 50-mLcentrifuge tubes (THF method); desiccator;reagent bottles with ground glass stoppers;drying oven; polyethylene wash hot sheet, to 1 mm , CRYSTALLINE, by XRD: METHOD 7500 , Issue 4, dated 15 March 2003 - Page 3 of 9 NIOSH Manual of Analytical Methods (NMAM), Fourth EditionSPECIAL PRECAUTIONS: Avoid inhaling silica dust [3]. THF is extremely flammable and should be usedin a fume hood. 2-Propanol, parlodion and isopentyl acetate are flammable.

7 Hydrochloric acid is corrosiveand should be used in a fume hood. each personal sampling pump with a representative sampler in at 5% L/min with nylon cyclone or 5% L/min with HD cyclone for a total sample sizeof 400 to 1000 L. Do not exceed 2 mg dust loading on the 1:Do not allow the sampler assembly to be inverted at any time when using a cyclone. Turningthe cyclone to anything other than a horizontal orientation may deposit oversized materialfrom the cyclone body onto the 2:A single sampler/flow rate should be used for a given application. Sampling for bothcrystalline silica and coal mine dust should be done in accordance with theISO/CEN/ACGIH/ASTM respirable aerosol sampling convention. Flow rates of L/min forthe Dorr-Oliver nylon cyclone and L/min for the Higgins-Dewell cyclone have been foundto be optimal for this purpose.

8 Outside of coal mine dust sampling, the regulatory agenciescurrently use these flow rates with the Dorr-Oliver cyclone in the United States and theHiggins-Dewell sampler in the United Kingdom. Though the sampling recommendationspresented in a NIOSH Criteria Document have been formally accepted by MSHA for coalmine dust sampling, the Dorr-Oliver cyclone at L/min with conversion factor iscurrently used in the United States for the purpose of matching an earlier samplingconvention [12]. In any case, a single sampler/flow rate should be used in any givenapplication so as to eliminate bias introduced by differences between sampler types andsampler conventions [11]. an area air sample or collect a settled dust sample, if dust in the work environment has not beenpreviously may be characterized by one of the following methods, as check.

9 Prepare area dust sample or settled dust bulk sample for XRD analysis bymounting the collection sample directly on an XRD sample holder, or by depositing or redepositingthe dust on another filter for mounting, or by packing an XRD powder holder. Proceed to step Analysis. Prepare the area air sample or settled dust sample for qualitative analysisby grinding and/or wet sieving to best match the airborne dust particle size. Wet sieve with a 10-:msieve, 2-propanol, and an ultrasonic bath [13], followed by evaporation of excess alcohol, drying inan oven for 2 hours, and overnight storage in a desiccator. Deposit the end product on a filter(steps 7-8) or pack in a conventional XRD powder 1:For quantitative determination of % SiO2, weigh out, in triplicate, 2 mg sieved dust ,transfer to a 50-mL beaker, add 10 mL 2-propanol, and continue with step 6.

10 NOTE 2:In a bulk sample, if there is an interfering compound(s) that renders theidentification and quantitation of quartz very difficult, the sample will need to be carefullytreated in hot phosphoric acid [14] to dissolve the interfering compound(s) and avoid theloss of quartz. This treatment can be used to dissolve several 50-mg sample aliquotsin order to concentrate the quartz content for the purpose of lowering the Use one of the following methods to prepare filter samples and Temperature Ashing: Place the filters in 50-mL beakers within the low temperature asherso that the sample exposure to the plasma is optimized. Ash according to manufacturer'sinstructions. After ashing, carefully add 15 mL 2-propanol to each beaker; Furnace the samples contain a significant amount of calcite (>20% of total dust loading), silica may belost due to formation of CaSiO3.