WPI APOLLO 4000, Instruction Manual

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APOLLO 4000
NITRIC OXIDE DETECTION
WORLD PRECISION INSTRUMENTS C-18
Measurement of NO
It is impossible to outline in detail how to use NO sensors to measure NO in every
experimental set up the user may encounter. There are, however, some guiding
principles of which the user should be aware to exploit fully the capabilities of the
technology. These are outlined below.
NO Delivery
For any measurement of NO to be made, the NO must reach the sensor surface so
it can react on the surface of the electrode. This point is of particular concern
because in many experiments the lifetime of NO is quite short. This is especially so
in biological systems where compounds such as hemoglobin can reduce the half-
life of NO to less than a second. It is therefore very important that the experimental
set up is designed so as to maximize delivery of NO to the sensor. In particular, the
tip of the sensor should be placed as close as possible to the site of release of NO.
Durability and Handling
The user must excercise caution when handling any NO sensor to avoid actions
which could damage the sensor tip. The sensor membrane and membrane coat-
ings are extremely delicate and improper handling will lead to damage.
Environmental Influences
There are two environmental parameters to which NO sensors are quite sensitive:
temperature and electrical interference, both of which are discussed in greater
detail below.
Temperature
Note that the sensitivity of the NO sensor is temperature-dependent. This is due to
the effects of temperature on the partial pressure of NO in either liquid or gas
samples, on the permeability of the membrane or coatings, and on the
conductivities of various circuit components. It is therefore recommended that any
calibration is performed at the same temperature as the experiment.
Electrical Interference
Although nitric oxide monitoring using the Apollo 4000 involves the measurement
of extremely small currents ( e.g., less than 1 pA), the intrinsic noise level of the