Recently I learnt how to analyze total mercury in environmental samples using the Direct Mercury Analyzer. As my research primarily focuses on environmental organic chemistry, I was amazed how quickly the concentration data can be retrieved starting from the fresh samples: 1min sample weighing time + ~5 min instrument time. As many as 100 samples and QCs can be analyzed in a batch
As a comparison, PCB analysis from air samples (hundreds of have I analyzed!) : Soxhlet extraction (18 h) or ASE (40 min) + rotoevaporation (30 min) + Column (2h) + nitrogen evaporation (~6-8h) + instrument time (~60 min) + chromatogram processing time (need to double check auto integration of the peaks in the chromatogram 10 min)
So how does this amazing DMA work?
Direct mercury analysis incorporates thermal decomposition, catalytic conversion, amalgamation, and atomic absorption spectrophotometry.
Controlled heating stages first dry and then thermally decompose a sample introduced into a
quartz boat. A continuous flow of oxygen carries the decomposition products through a hot catalyst bed where halogens, nitrogen, and sulfur oxides are trapped. All mercury species are reduced to Hg(0) and are then carried along with reaction gases to a gold amalgamator where the mercury is selectively trapped. All non-mercury vapors and decomposition products are flushed from the system
by the continuous flow of gas. The amalgamator is subsequently heated and releases all trapped mercury to the single-beam, fixed-wavelength atomic absorption spectrophotometer. Absorbance
is measured at 253.7 nm as a function of mercury content.
Image source: http://media.americanlaboratory.com/m/20/Article/502-fig2-zoom.jpg
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