Operating instructions

1. General Description page 9
Mercury Instruments UT-3000-E_V2.11.docx 31.07.12
Analytical Technologies
Pump
Mass flow
meter
Optical Cell
GoldTrap
V2
V1
Zero air
filter
0.45 µm
PTFE filter
Calibration
port
UT-3000 Mercury Ultratracer
Sample IN
40 l/h
10 l/h
1.2 Measuring principle
The UT-3000 uses the Mercury Instruments GoldTrap to capture total gaseous mercury (TGM)
directly from the sample. GoldTraps work because mercury sticks to gold at room temperature.
The sample gas is pulled through a 0.45 micron PTFE filter and then passes the trap. The gas
continues to flow through the trap but the mercury stays behind--trapped on the gold. After the
mercury is captured, the GoldTrap is heated very quickly; this releases the mercury as a gas
(thermal desorption). The gaseous mercury is then swept by the flow of purified mercury free air
into the optical cell of the detector. Here the mercury is measured by atomic absorption
spectrometry (AAS).
Basis for determination of the mercury concentration by AAS is the resonance absorption of the
Hg-atoms at a wavelength of 253.7 nm. The sample gas is carried into the optical cell by a built-
in pump. The optical cell is entirely made of synthetic quartz glass. Radiation of a mercury lamp
passes through the cell and is measured by a solid state detector. The attenuation of the UV light
reaching the detector depends on the number of mercury atoms in the optical cell. The
microprocessor performs the quantitative evaluation of the mercury concentration in the sample.
In order to get an extremely stable baseline, the UV-light source is controlled by a reference
beam and reference detector device. In addition to this, the UV detectors of the UT-3000 are
thermostatically controlled. Heating the optical cell and the GoldTrap makes the UT-3000
insensitive to volatiles like water vapor and hydrocarbons.
F IGURE : UT-3000: S CHEMATIC GAS FLOW