Mercury Research Laboratory

Standard Filtration Procedure

This procedure describes how to assemble the filtration equipment and process a whole-water sample to obtain clean subsamples for particulate or filtered mercury, or both. This procedure works best for grab samples intended for standard mercury analysis (non-isotopic). Please contact us for guidance if your application is volume limited or is intended for natural isotope abundance measurements.

Instructions

 1.  Wearing clean nitrile gloves, assemble filtration apparatus by connecting the ¼” x ¼” union (B) to the dome of filtration chamber (A).

Diagram of particulate filtration setup for pouring water through filter

2. Place clamp nut (D) over the ¼” union with the knurled/threaded end facing up. If not already assembled, insert tube (C) into the compression fitting on filter holder (E) and tighten.  Place the open end of this tube through the ¼” union (B) and tighten. 

3. Place a clean quartz fiber filter (F) onto filter holder (E) using Teflon tweezers (filters are precleaned by heating to 550° C for 2 hours).  Set the reservoir (G) on top of the filter (F). Tighten clamp nut (D) onto reservoir. Note: If filtering for Suspended Particulate Matter (SPM), individual cleaned & pre-weighed filters are provided in separate clear plastic cases. These filters can also be analyzed for particulate methylmercury.

Illustration of particulate filtration setup for pouring water through filter

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. Tip: Pre-rinse the bottle with blank water to remove residual acid. If mercury-clean blank water is not available, adjust steps 6 & 7 to first include a small rinse of the bottle with filtered sample.

6. Homogenize the sample thoroughly and fill the reservoir. 

7. Apply vacuum to the chamber and continue adding sample to the reservoir until at least one liter of water has been filtered. This volume can be adjusted up or down depending on the suspended particulate load. Tip: If extra sample is available, filter at least 1.2 L for particulate methylmercury samples.

8. Once the sample is completely filtered, break the vacuum and remove the quartz fiber filter (F) with the Teflon tweezers. Place the filter into a stackable Teflon petri dish (SPM filters are returned to their plastic case). Apply one of the matching bar code labels to the Request for Analysis form and keep the second label stacked in the same order as the petri dishes. Note: SPM filters will have one barcode pre-applied to the case and the second label is for the Request for Analysis form.

9. Determine post-weight of the sample. The difference between the pre- and post-weights determines volume filtered. Record this value on the Request for Analysis form.

10. (Figure 3) Petri dishes are combined into stacks by analysis type (separate stacks for methyl and total mercury). Cap each Teflon stack with an empty petri dish and place the corresponding barcodes into the empty dish at the top. Carefully secure the stacks by wrapping lengthwise with labeling tape (Figure 4) and clearly marking the tape with the project, date, and analysis type (PTHG or PMHG). Place secured stacks into two zip-seal bags and keep frozen until processed for analysis. 

11. Filters should be analyzed within 1 year of sample collection and freezing. 

Contacts

Sarah E Janssen

Research Chemist
Upper Midwest Water Science Center
Phone: 608-821-3976