Page:NIOSH Manual of Analytical Methods - 7500.pdf/3

 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