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helium for 30 minutes to remove Oz. The water is then bubbled with pure NO (>99.0Vo1) for
30 minutes in a glass sampling bulb. Samples can be aspirated through a rubber gas-tight
syringe. Before aspiration Nz should be injected into the glass bulb to exclude Oz (Archer
1993). Once a saturated NO solution has been made serial dilutions of the NO gas or solution
can be made using deoxygenated HzO. Having reviewed the alternatives, the company that I
used was BOC Gases (Suney Research Park, Guildford, Suney, United Kingdom) who were
local to where the research was taking place and who regularly supplied gases to the Royal
Brompton Hospital. Also they could provide NO in cylinders of appropriate concentrations
suitable for calibration of the levels we intended to measure (see below).
Whether personal or commercial preparations of NO are being made for calibration purposes
it is imperative to avoid contamination with Oz which will reduce the NO in the sample. Zero
calibration can be done with NO free certified compressed air. Alternatively, passing room air
though the ozone generator of the chemiluminescence analyser, which converts all NOx to
nitrogen dioxide and then passing the resultant gas through soda lime and activated charcoal
to remove the NOz and ozone respectively can also produce NOx free air. The most useful
calibrations gas concentrations are zero and concentrations within the usual levels measured,
with the final calibration just above the highest levels likely encountered to avoid the need for
linear extrapolation beyond the range. Not all the companies could provide appropriate
concentrations or had them in stock. In normal subjects on the current analysers with the
current measurement protocols, the range is 0-25ppb for oral exhaled NO and 250-1000ppb
for nasal NO but the levels on the older machines were often higher (0-80ppb) for oral
exhaled measurements. The reason for these differences will be come clear when reviewing
the methodology experiments that I completed (see Chapter 5). I always had a zero and two
NO cylinder concentrations for calibration for the experiments described in the work of this
thesis. They were either 27ppb and 103ppb and ll0ppb or 55ppb and 118ppb when the first
cylinders were exhausted.
4.6.2 Safety and toxicity
In the final part in this chapter I want to review the toxicity of NO, and the two gases
generated using the chemiluminescent technique -
NOz and ozone. The reactions and effect of
NO at the cellular level has been covered in Chapter 3 sections 3.2 'Properties of nitric oxide'
and 3.3 'Reactions of nitric oxide'. NO must be handled with care -
the toxicity of NO is due
to the gas itself and also the interactions that occur with oxygen when it forms a dimeric form
of NOz - a reddish brown toxic gas @udvari, O'Neil et al. 1989) which in high 02
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