Total mercury (Hg) analyses for the Finger Lakes Hg Project are carried out on a Milestone Direct Hg Analyzer, the DMA-80 (pictured below). A direct Hg analyzer is a treat to work with, as it only takes about 5 minutes to get a result! There are no sample digestion or wet chemistry pre-treatment steps, and this method does not generate any chemical waste.
First you weigh your tissue, which can be either wet or dry, into the sample boats. For our dried fish tissues, we use the nickel boats pictured above. The boats are placed on the autosampler, and then DMA-80 operates as follows:
Step #1 Decomposition
The sample is moved into a furnace, where it is dried and thermally decomposed using oxygen. Any Hg in the sample will now exists as Hg vapor (Hg0). The Hg vapor and decomposition products move into a second furnace that burns off any impurities.
Step #2 Amalgamation
The Hg vapors are selectively trapped on a gold amalgam and then rapidly heated (to 850C/1562F in 12 seconds!) so that the Hg is released and then can be measured.
Step #3 Atomic Absorption
The Hg content is measured using atomic absorption spectrophotometry at 254 nm.
This method is fully compliant with the US EPA Method 7473 for determination of Hg in solids and solutions.