5. 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 sample exposure to the plasm a is optim ized. Ash according to manufacturer'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 CaSiO3. Remove the calcite by the following procedure: Place a 0.5-:m,
25-mm PVC filter in the filtration apparatus and clamp the filter funnel over it. Remove the
sample filter from the cassette, fold, and drop it on the 25-mm filter. Add 10 mL 25% v/v HCl and
5 mL 2-propanol to the filter funnel and allow to stand for 5 min. Apply vacuum and slowly
aspirate the acid and alcohol in the funnel, washing with three successive 10-mL portions of
distilled water. Release the vacuum. Carry both filters through the ashing step together.
ii. Place the filter samples in porcelain crucibles, loosely cover and ash in muffle furnace for 2 h at
600 °C (800 °C if graphite is present). Add several m L 2-propanol to the ash, scrape the crucible
with a glass rod to loosen all particles and transfer the residue to a 50-mL beaker. Wash the
crucible several more times and add wash to beaker. Add 2-propanol to the beaker to bring the
volume to about 15 mL; or
5. 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 asherso that the sample exposure to the plasm a is optim ized. Ash according to manufacturer'sinstructions. After ashing, carefully add 15 mL 2-propanol to each beaker; orb. Muffle Furnace Ashing:i. If the samples contain a significant amount of calcite (>20% of total dust loading), silica may belost due to formation of CaSiO3. Remove the calcite by the following procedure: Place a 0.5-:m,25-mm PVC filter in the filtration apparatus and clamp the filter funnel over it. Remove thesample filter from the cassette, fold, and drop it on the 25-mm filter. Add 10 mL 25% v/v HCl and5 mL 2-propanol to the filter funnel and allow to stand for 5 min. Apply vacuum and slowlyaspirate the acid and alcohol in the funnel, washing with three successive 10-mL portions ofdistilled water. Release the vacuum. Carry both filters through the ashing step together.ii. Place the filter samples in porcelain crucibles, loosely cover and ash in muffle furnace for 2 h at600 °C (800 °C if graphite is present). Add several m L 2-propanol to the ash, scrape the cruciblewith a glass rod to loosen all particles and transfer the residue to a 50-mL beaker. Wash thecrucible several more times and add wash to beaker. Add 2-propanol to the beaker to bring thevolume to about 15 mL; or
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