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Principle of
Operation
Thermo Scientific
The 42iQTL operates on the principle that nitric oxide (NO) and ozone
(O
) react to produce a characteristic luminescence with an intensity
3
linearly proportional to the NO concentration. Infrared light emission
results when NO
molecules decay to lower energy states. Specifically:
2
NO
+
O
Nitrogen dioxide (NO
be measured using the chemiluminescent reaction. NO
NO by a molybdenum NO
The ambient air sample is drawn into the 42iQTL through the sample
bulkhead, as shown in
and then to the mode solenoid valve.
The mode solenoid valve determines whether the sample flows through the
NO
-to-NO (NO
mode) or bypasses the NO
2
x
mode). The sample then flows through the converter output valve and a
flow sensor to the prereactor solenoid valve.
The prereactor solenoid valve directs the sample either to the reaction
chamber, where it mixes with ozone to give an NO reading, or to the
prereactor, where it reacts with ozone prior to the reaction chamber giving
a dynamic zero reading for the analyzer. The prereactor is sized so that
greater the 99% of a 200 ppb NO sample will react prior to entering the
reaction chamber, yet is small enough to allow other potential interferents
to pass through to the reaction chamber.
Dry air enters the 42iQTL through the permeation dryer, passes through a
flow switch, and then through a silent discharge ozonator. The ozonator
generates the ozone needed for the chemiluminescent reaction. At the
reaction chamber, the ozone reacts with the NO in the sample to produce
excited NO
molecules. A photomultiplier tube (PMT) housed in a
2
thermoelectric cooler detects the luminescence generated during this
reaction.
The NO and NO
concentrations calculated in the NO and NO
x
are stored in memory. The difference between the concentrations is used to
calculate the NO
concentration. The 42iQTL outputs NO, NO
2
NO
concentrations to the front panel display and the analog outputs, and
x
also makes the data available over the serial or Ethernet connection.
+
+
h
NO
O
3
2
2
) must first be transformed into NO before it can
2
-to-NO converter heated to about 325 °C.
2
Figure
1–2. The sample flows through a capillary,
Introduction
Principle of Operation
is converted to
2
-to-NO converter (NO
2
modes
x
, and
2
42iQTL Instruction Manual
1-3
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