Mercury European Pharmacopoeia

Mercury can exist in two ionic forms The mercury(I) ion which is foxmd as the dimer Hg2 +, and the mercury(II) ion Hg +. Mercury is unique because it is the only metallic element that is a liquid at room temperature. The chemistry of mercury(I) and mercury(II) is quite different and this allows differentiation using the two tests described. Mercury lies above copper in the electrochemical series, which is used in test (a) as an identification of mercury(ll) and mercury(II). Mercury(II) forms an insoluble oxide of a characteristic color and this is used in test (b). 

In the first step of analysis, about 0.1 ml of a solution of the substance to be examined is placed on a piece of copper foil. When a solution containing or Hg2+ is brought in contact with metallic copper, a redox reaction takes place. 

This transfer of electrons takes place spontaneously since the reactions 

As a result of this, metallic mercury will be formed from the ionic mercury ions presents in the test solution and reveal itself as a dark gray stain that becomes shiny on rubbing, using, for example, a dry doth. Since mercury is volatile, it will evaporate when the foil is heated in a test tube as dictated in the second step of analysis. The foil used has to be well-scraped since 

This forms a protective layer that would prevent the mercury ion from coming in contact with metallic copper. 

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Determinations of very small amoxmts of arsenic, such as 0.1 mg or less, were traditionally done with the Marsh test or the Gutzeit test invented in the late nineteenth century. Method (a) of the European Pharmacopoeia can be considered a modified Gutzeit test, but whereas this originally used silver nitrate or mercury(II)chloride to detect any arsenic present, method (a) uses mercury(II)bromide. 

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