FED-STD-791D
6.2.1 Insert a new membrane filter into the filter holder, and filter three 100-mL portions
of distilled water to rinse the filter flask. Discard the rinsings.
6.2.2 Continue filtering enough distilled water to rinse each of the three prepared sample
bottles (see 6.1 through 6.1.5) and stoppers with three 100-mL portions, and to fill one of them
with filtered distilled water; stopper them immediately.
6.2.3 Replace the used filter with a new one, and using the cleaned filter flask, filter
enough isopropyl alcohol to rinse the two clean sample bottles and stoppers with three 100-mL
portions and to subsequently fill one with filtered alcohol; stopper them immediately.
6.2.4 Using a new filter, filter enough petroleum ether to rinse (with three 100-mL
portions) and subsequently fill the last sample bottle; stopper immediately.
6.2.5 Remove the filter holder from the filter flask, and discard the used filter.
6.3 Using tongs to handle them, prepare two glass slides as follows:
6.3.1 Soak in hot glass-cleaning solution until clean.
6.3.2 Rinse with filtered, distilled water.
CAUTION: Immediately re-stopper the sample bottles after each use to avoid contamination.
6.3.3 Rinse with filtered isopropyl alcohol.
6.3.4 Rinse with filtered petroleum ether and allow to air dry.
Caution. Isopropyl alcohol and petroleum ether are flammable. Use only in a
NOTE 1:
well ventilated area. Keep all flames away from these materials.
6.3.5 When dry, immediately hinge the two slides together, using transparent tape, and
store them in a clean covered petri dish.
6.4 Using tongs, prepare the filter holder for the filtration of the sample as described in
6.4.1 through 6.4.3.
6.4.1 Rinse the filter holder and the funnel cover, first with filtered distilled water,
then with filtered, distilled isopropyl alcohol, and finally with filtered petroleum ether.
6.4.2 Using clean forceps to grip the edge, rinse a new membrane filter with filtered
petroleum ether, and install it (grid side up) on the fritted glass surface of the filter holder. Also,
install a filter in the cover for the graduated funnel.
6.4.3 Install and clamp the funnel to the filter holder. Ground the clamp (to prevent
buildup of static electricity while filtering).
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