CETAC M-7600 Mercury Analyzer Operator's Manual

Operator’s Manual
Chapter 4: Using the Analyzer
Ultimately, the gas stream (carrier gas and Hg 0 ) exits the sample cell (15) and
is exhausted to a solid KMnO 4 trap (16) where Hg 0 is absorbed, and clean
carrier gas passes to the lab atmosphere.
Dryer Cartridge
The mercury analyzer uses a Perma Pure ® DuPont Nafion ® -based dryer
cartridge. Dryer cartridges typically last three to six months.
The dryer cartridge contains Perma Pure ® dryer tubing which is made with a
tubular DuPont Nafion ® membrane. The Nafion ® tubing is housed within an
outer tube and coiled inside the cartridge. The argon or nitrogen carrier gas
containing mercury and water vapor is swept along the inner Nafion ®
membrane, allowing water vapor to permeate the membrane selectively,
whereas the membrane is not permeable to mercury vapor. On the “waste” side
of the membrane, a counter gas flow, split from the carrier gas supply,
selectively sweeps the water vapor out of the system, whereas non-permeating
mercury vapor proceeds to the sample cell.
The Perma Pure ® dryer cartridge and associated plumbing is already preinstalled
in your new QuickTrace M-7600 factory shipment. No further
installation is required.
Optics and Cold Vapor AAS
Refer again to Figure 4-1 on page 76 to trace the optical path of the
QuickTrace M-7600. The Cold Vapor AAS (Atomic Absorption Spectrometry)
process within the sample cell begins with a low pressure, high frequency,
thermally stabilized, electro-optically regulated Hg vapor lamp, which
produces the Hg emission spectrum. Emitted light is collimated (L 1) and
projected in two parallel, isolated beams one each through the reference and
sample cells. Absorbance of 253.7nm radiation by Hg 0 vapor (derived from the
chemically reduced sample and GLS) occurs only in the sample cell. P is
thereby decreased, relative to P 0.
Light from the cells enter the binocular camera, where both collimated beams
are independently focused (L 2) and filtered (F) before reaching the Charged
Coupled Device (CCD) detector. Narrow band 254 +/- 2nm interference filters
(F) remove all radiation but the strong 253.7 nm Hg 0 “resonance line” from
both the sample (P) and reference (P 0) beams. By a photovoltaic effect, the CCD
converts the light beams into electrical signals, proportional to radiant power
(P and P 0). These outputs are processed to yield an electrical signal
proportional to optical absorbance (Abs = -log (P/P 0)).
Software
In the host computer, the sample absorbance value is drift corrected, blank
subtracted, if through blank is desired. The absorbance value is then measured
against a calibration curve derived from previously obtained absorbance
values of calibration standards.
The QuickTrace software operates under a Windows environment. The
QuickTrace software provides complete instrument, autosampler control.
The QuickTrace software also provides a variety of EPA compliant quality
control functions, display features, report generation and diagnostic routines.
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