Page:NIOSH Manual of Analytical Methods - 7601.pdf/2

 SILICA, CR YST ALLINE : MET HO D 760 1, Issue 3, dated 15 M arch 200 3 - Page 2 o f 6 REAGENTS:

EQUIPMENT:

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. Hydrofluoric acid, 48% (HF ).* 3. O rthopho sp ho ric ac id, 8 5% H 3PO 4.* 4. Silica-free water. All water used must be deionized and stored in polyethylene containers. 5. Hydrochloric acid (H Cl),* 1:10 v/v conc. HCl in deionized water. 6. Sulfuric acid, 10 N.* Cautiously add 555 mL con c. H 2SO 4 to about 1.3 L of deionized water. Cool. Dilute to 2 L. 7. Nitric acid, co nc.* 8. Perchloric acid, conc*. Use only if samples have been collected on PVC filters. 9. Bo ric acid solution, 5%. 200 g boric acid crystals in 4 L w arm deion ized water. C ool. Filter with vacuum through a 0.45-:m mem brane filter. Store in a polyethylene container. 10. Molybdate reagent. Dissolve 50 g amm onium molybdate tetrahydrate in about 400 mL deionized water. Ad d 50 m L conc. s ulfuric acid. Cool. Dilute to 500 mL. Store in dark. 11. Reducing solution. Dissolve 9 g sodium bisulfite in 80 mL deionized water. In 10 mL deionized water, dissolve 0.7 g anhydrous sodium sulfite and 0.15 g 1-am ino-2-naphth ol4-sulfonic acid, in that order. Com bine these solutions and dilute to 100 mL with deionized wa ter. Sta ble about one m onth if sto red in refrigerator. 12. Silica stock standard, 0.5 m g/m L. Dissolve 250 m g qu artz in 10 m L 48 % HF. Dilute to 500 mL with silica-free water. Store in a polyeth ylene contain er. Sta ble indefinitely.

1. Sam pler: a. Filter: Mixed ce llulose ester (MC E) filter, 37-mm, 0.8-:m, or polyvinyl chloride (PVC) filter, 37-mm, 5.0-:m pore size, supported with backup pad in a two-piece, 37-m m cassette filter ho lder (preferably, conductive) held together by tape or cellulose shrink band. NOTE: If PVC filters are u sed, a perchloric acid fume hood, lowtemperature radio-frequency plasma asher or muffle furnace will be needed to ash them (Appen dix B). 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 a two-piece filter cassette. Sample closed face at 3 L/min. 3. Sam pling pumps: HD cyclone, 2.2 L/min; nylon cyclone, 1.7 L/m in; and area sam pler, 3 L/min. 4. Precision heater, 550-watt, 115-V, Type RH; 750-wa tt variable transform er with built-in voltmeter; variable speed clinical rotator, about 30 to 80 rpm range (can be achieved with a variable transform er). 5. Stopwatch or laboratory timer. 6. Phillips beakers, borosilicate glass, 250-mL; short-stemmed glass funnels with bent stems (must be done by laboratory); crucible tongs with tygon or rubber-padded tips; polyethylene stirring rods; polyethylene 50mm discs. 7. Vacuum filtration assembly: MCE m embrane filters, 0.45-:m pore size, 47-m m diame ter; filter funnel, including mem brane mount and flask asse m bly, 47-m m. 8. Buret, polypropylene, 10-mL; polyethylene reagent bottles for water, boric acid, and standard solutions. 9. Constant temperature bath, 40 °C. 10. Spectrophotometer, at 420 to 820 nm and 1cm cuvettes. 11. Hotplate, 150 °C surface temperature. 12. Graduated cylinder or graduated pipet, 10and 25-mL. 13. Polyethylene graduated cylinder or pipets, 25- and 5-mL.


 * See SPECIAL PRECAUTIONS.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition