National Institute for Occupational Safety and Health

“ Recovery of quartz is low and precision is much worse if quartz only is present during the pho sph oric acid treatm ent. NOTE 1: Calibration standards are limited to specified NIST and USG S certified standards of known purity, particle size and sam ple-to-sam ple hom ogeneity. At least 12 materials including 5 μm Min-U-Sil previously used by laboratories throughout the United States and Canada have been evaluated. None have be en fo und to be acceptable alternatives to the certified standards cited within this m ethod [3] . Standard reference materials should be corrected for ph ase purity. ”

“ 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. ”

“ Preheat the heater and adjust to maintain a tem perature of 240°C. Heat each sample and blank for exactly 8 min, swirling it by the action of the variable speed rotator. NOTE: The solution in the flask should reach 240°C during this procedure. Rem ove the beaker from the heater with padded tongs and swirl it for 1 min. Allow the be aker to cool. Ad d about 125 m L warm (60 to 70°C) de ionized water and swirl to m ix com pletely. Filte r the sam ple with suctio n through a 47-m m filter. W ash thoroughly with 1:10 H Cl. Place the 47-m m filter in the bottom of a 1 50-m L po lyethylene bea ker. ”

“ Polyethylene graduated cylinder or pipets, 25- and 5-mL.
See SPECIAL PRECAUTIONS. NIOSH Manual of Analytical Methods (NMAM) , Fourth Edition SILICA, CR YST ALLINE : MET HO D 760 1, Issue 3, dated 15 M arch 200 3 - Page 3 o f 6 SPECIAL PRECAUTIONS: Avoid inhaling silica dust [5] . Use pers ona l protec tive equipm ent to prevent contact of acids with the skin. HF dissolves glass. Use plastic labware for all solutions containing HF. Concentrated acids are corrosive.
SAMPLING: 1. Calibrate each personal sampling pump with a representative sampler in line. 2. ”

“ If a perchloric acid hood is not available, see APP EN DIX B for alternate ashing procedures for PVC filters. Pretreatment proc edu res to rem ove variou s co ntam inants from bulk sam ples are o utlined in referenc e [7] . ”