Page:NIOSH Manual of Analytical Methods - 7601.pdf/6

 SILICA, CR YST ALLINE : MET HO D 760 1, Issue 3, dated 15 M arch 200 3 - Page 6 o f 6 APPENDIX B: ALTERNATE ASHING PROCEDURES FOR PVC FILTERS If a perchloric acid fume hood is unavailable, ash PVC filters with one of the following methods. 1.

M uffle furnace ashing: W ash the filters with 25% v/v HC l if the samples contain a significant amount of calcite (20% of the total dust loading); otherwise, proceed to next paragraph. Place a 0.5-:m, 47-m m PVC filter in the filtration apparatus. Center the sample filter on top of the first filter. Clamp the filter funnel over the frit so that th e dust deposit is completely exposed. Add 10 mL HC l solution and 5 mL 2-propanol to the filter funnel; allow to stand for 5 min. Apply vacuum to aspirate the acid/alcohol solution from the filter. W ash with three 10-mL portions of deionized water. Release the vacuum. Place the filter sam ples in porcelain crucibles, co ver loo sely and ash in a muffle furnace for 2 h at 600 °C (800 °C if graphite is present). Add several m L of 2 -propan ol to the ash, scra pe the cru cible to loosen all particles and transfer the residue to a 250-mL borosilicate glass Phillips beaker. W ash crucible several times and add wash to the beaker. Heat on a sparkless hotplate to evaporate the 2-propanol. W hen beaker is dry, proceed with step 4 of sample preparation.

2.

Low temperature ashing: Place the filters in 50-mL glass beak ers within the LT A s o that th e sam ple expos ure to the plasm a is o ptim ized. Ash accord ing to m anufa cturer's instructions. After ashing, add 2-propanol to the beaker to transfer the residue to a 250-mL borosilicate Phillips beaker. W ash the beaker with 2-propanol several times, adding the washings to the Phillips beaker. Heat on a sparkless hotp late to remove the 2-propanol. W hen the beaker is dry, proceed to step 4 of sample preparation.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition