Compounds eluting from the column pass directly into a heated bed of mercuric oxide (HgO).Within this bed, the following general reaction occurs:

X + HgO (solid) => XO + Hg (vapor)

where X is any appropriate reducing gas.The liberated mercury vapor is quantitatively determined utilizing an ultraviolet (254nm)absorption photometer located immediately downstream of the bed. The relative ease of measuring mercury vapor at low concentrations lends the technique itsinherent sensitivity.

For carbon monoxide and hydrogen, the equilibrium reactions are as follows:

CO + HgO (solid) => CO2 + Hg (vapor)

H2 + HgO (solid) => H2O + Hg (vapor)