The Cost Benefits of Direct Mercury Analysis

How do you know the bottom line?

Imagine you are the owner of a large contract laboratory, and are beginning to get more and more requests for mercury analysis. You have always used a traditional dedicated mercury analyzer utilizing cold vapor atomic absorption or atomic fluorescence spectrometry (CV-AAA or AFS), which are well suited for liquid samples with low mercury content including drinking water and surface waters. However, for the solid and other liquid samples that came into your lab, they had to go through an appropriate dissolution step prior to analysis, which in many cases involved microwave digestion. And because of the high volatility of mercury, these dissolution techniques can often lead to loss of analyte and poor recoveries if the optimum digestion technology isn’t used, possibly resulting in sample reruns, which can impact lab efficiency, operator time, and the overall cost of analysis.
Most of your current workload involves different types of environmental samples, which makes it very challenging for your lab to match all these requirements with a single technique. In addition, EPA Method 7471 for measuring total mercury in soils, sediments, bottom deposits, and sludge-type materials using cold vapor atomic absorption that you have used for years requires daily calibration and is prone to interferences from specific species including sulfide, chloride, and copper ions. They necessitate the use of oxidizing and reducing agents to ensure they were in the appropriate oxidation state before the mercury vapor is reduced and swept into absorption cell. For this reason, the EPA method definitively states that “it should be carried out with properly experienced and trained personnel and that each analyst demonstrates the ability to generate acceptable results with this method.”
So, with this information fresh in your mind, it has you thinking that a novel approach known as Direct Mercury Analysis (DMA) that can determine mercury directly in solid and liquid samples using the principle of thermal decomposition coupled with amalgamation and atomic absorption might be the way to go. In this technique, the sample is thermally decomposed in a metallic or quartz boat and introduced into a quartz tube, where a continuous flow of air carries the decomposition products through a hot catalyst bed where halogens, nitrogen, and sulfur oxides are trapped. All mercury species are reduced to elemental mercury (Hg0) and then released into a gold amalgamator where the mercury is selectively trapped, heated, and passed into a fixed wavelength atomic absorption spectrophotometer for detection.

Cost of analysis

So, with this analytical scenario as background information, let’s take a more detailed look at the cost of analysis comparison between a dedicated mercury analyzer and one using Direct Mercury Analysis. It’s also worth noting that there are three approved methods using this approach - EPA Method 7473 for solid samples and liquids (3), ASTM method D-7623-10 for total mercury in crude oil using combustion gold amalgamation and cold vapor atomic absorption method (4) and ASTM 6722-01 for coal combustion products (5). The EPA method states that total mercury can be determined in either the laboratory or a field setting without sample chemical pretreatment in less than 5 minutes.
You know that over the next 12 months you’ll be getting a high workload of samples, so it sounds ideally suited for what you want to do. However, you are unsure if the cost savings can justify the investment for a new Direct Mercury Analysis instrument.
This is the exact scenario that many labs are faced with when the demand for mercury analysis increases significantly. To stay with traditional dedicated mercury techniques such as CV-AAS/AFS or perhaps move some of the samples over to the ICP mass spectrometer (ICP-MS), which is predominantly used for drinking water and wastewater analysis, or to invest in the direct mercury technique. So, let’s take a closer look at the comparison in running costs between the Milestone DMA-80 evo and CV-AAS/AFS, and also how they stack up against ICP-MS, to see if the investment can be justified.
Note: For this exercise, we’ll make the comparison using similar sample types that require some type of sample pretreatment or preparation (e.g., solids or liquids that require digestion).

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