3.3 Local Environment
Amperometric detection is a highly sensitive technique. The currents measured typically fall
in the picoampere or nanoampere range. Hence, smooth operation can easily be influenced
by electrical disturbances in the environment. Also, since detection is due to a chemical re-
action, its response (and baseline drift) is temperature-dependent; this is very noticeable at
high detector gain.
The new design of the LC-44 Amperometric Detector decreases the influence of these prob-
lems. It offers significant advantages over earlier models. The Preheater Module, when con-
trolled by the LC-22C Temperature Controller, eliminates long-term drift due to room tem-
perature fluctuations. The new flowcell design is well shielded from stray capacitance prob-
lems; moreover, it is wholly contained within an easily opened, grounded compartment.
When selecting a location for the detector, follow these guidelines:
1.
Connect the entire chromatograph (pumps, detector, recorder, temperature controller, etc.)
to the same grounded power line. This ensures adequate ground to all components of
the system and eliminates the possibility of a ground loop, which could produce base-
line noise. Also, select a power line that is lightly used. Other laboratory instruments
such as ovens, vortex mixers, centrifuges, and large motors may cause spikes in the
power line.
2.
Locate the chromatograph on a stable bench. Vibrations can hamper the performance of
any sensitive instrument.
3.
Select a room where the temperature remains stable throughout the day. Avoid installing
the chromatograph near windows, air ducts, ovens, or refrigerators.
4.
Place the chromatograph away from busy, congested areas. Remote, isolated areas are
best for high-sensitivity work.
5.
Avoid very dry areas and areas that are carpeted. Static electricity can affect instrument
performance. Antistatic floormats and benchmats are useful if spiking caused by static
charge is a problem.
6.
Avoid areas where radio frequency interference is likely. Beeper-type paging devices can
be a problem in some installations.
Section 3. Installation
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