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NO2 produced can be removed by a soda lime column and resulting Og can be removed using
a charcoal column; or the exhaust can be immediately directed outside. I opted to use columns
to 'scrub' the compounds from the exhaust air. The luminescence signal as measured by a
photon counter and transmitted as an electrical signal and (in the early adapted machine which
we used) this was then transmitted to a chart recorder. In the later versions of the machine the
signal went to an analogue digital computer.
Sensitivity: The detection threshold of NO is 20-50pmol. In aqueous solutions the
chemiluminescence assay has been reported to detect as little as 10-13 M of NO
(Zafrnou and McFarland 1980). The chemiluminescence/1.{O curye has been
found to be linear between NO doses of 0-50pmol (Fontijn, Sabadell et al.
1970) and 300-3000 pmol (Menon, Wolf et al. 1989; Brien, Mclaughlin et al.
19e1).
Specificity: Chemiluminescence is almost exclusively due to NO. As mentioned above,
there are few other substances that react to produce light and these are either
non-volatile or are not biologically important such as the production of HzS
and alkenes. One author (Archer 1993) found that at very high levels a solvent
used for many drugs (dimethyl sulfoxide - 'DMSO') could also cause a
chemiluminescent signal. This is unlikely to be a problem in exhalate and
pertains more to the use of high dose chemicals on explanted or cultured tissue
(Mottu, Laurent et al. 2000). However this chemical is a known antioxidant
and more recently has been employed as a treatment in certain inflammatory
conditions, most particularly in interstitial cystitis (bladder inflammation), but
also for some rheumatologic diseases (Santos, Figueira-Coelho et al. 2OO3i
Chancellor and Yoshimura 2004; Parsons 2004).
The NO chemiluminscence analysers available in 1995 were designed for measuring NO
concentrations within 2-4000pbb and 40-400ppm range in a continuous ambient air sample.
They had been adapted for online recording and had a stabilised measurement capability as
measured by drift without using an auto zero over 24 hours. In most this was cited at between
zero and two ppb. They operated in ambient temperatures of 5-400 C and humidity of 0-95Vo.
The estimates of NO concentrations were decreased 10-15Vo at l00%o humidity, however NO
pre-drying of the expirate was not thought to be necessary for most environments @gure 4.2
does have a pre-drying unit added in the diagram). The original response time of these
machine developed to measure airway pollution were long, too long for the purpose that we
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