Particulate filtration in field samples
This procedure describes how to assemble filtration equipment and filter a field sample using mercury-clean equipment.
- (Figure 1.) Assemble filtration apparatus by connecting the 1/4-inch x 1/4-inch union (B) to filtration chamber (A).
- (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).
- (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.
- Determine the pre-weight of the sample to be filtered.
- Place an empty mercury-clean sample bottle inside chamber (A) so the mouth of the bottle lines up with the tube.
- Homogenize the sample thoroughly and fill the reservoir.
- 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.
- 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.
- Determine post-weight of the sample. The difference between the pre- and post-weights determines volume filtered.
- Petri dishes are combined into stacks, placed into two zip-seal bags, and frozen until processed for analysis.
- 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.