Particulate filtration in field samples

This procedure describes how to assemble filtration equipment and filter a field sample using mercury-clean equipment.

Filtration Procedure

1. (Figure 1.) Assemble filtration apparatus by connecting the 1/4-inch x 1/4-inch union (B) to filtration chamber (A).
2. (Figure 2.) Place clamp nut (D) over union. Insert tube (C) into the compression fitting on filter holder (E) and place other end of tube through the union (B).
3. (Figure 2.) Place an ashed (cleaned by heating to 550° C for 2 hours) quartz fiber filter (F) onto filter holder (E) using Teflon tweezers. Set the reservoir (G) on top of the filter (F). Tighten clamp nut (D) onto reservoir.
4. Determine the pre-weight of the sample to be filtered.
5. Place an empty mercury-clean sample bottle inside chamber (A) so the mouth of the bottle lines up with the tube.
6. Homogenize the sample thoroughly and fill the reservoir.
7. Apply vacuum to the chamber and continue adding sample to the reservoir until approximately 1 liter of water has been filtered. Volume can be amended, depending on the suspended particulate load.
8. Once the sample is completely filtered, break vacuum and remove the quartz fiber filter (F) with the Teflon tweezers. Place into a stackable Teflon petri dish.
9. Determine post-weight of the sample. The difference between the pre- and post-weights determines volume filtered.
10. Petri dishes are combined into stacks, placed into two zip-seal bags, and frozen until processed for analysis.
11. Filters should be analyzed within 1 year of sample collection and freezing.

Figure 1. Filtration chamber with assembled reservoir/filter assembly (detail in Figure 2).

Figure 2. Detail of reservoir/filter assembly. Shown assembled in Figure 1.