View - ResearchSpace@Auckland - The University of Auckland

function. This is especially important with biological specimens as proteinaceous material
(such as albumin and blood) foams during stripping and therefore provides more difficulties.
The chemiluminscence assay can also be used to measure the other intermediates and other
end products of NO oxidation such as s-nitrosothiols, nitrite and nitrate. The compounds can
be made to release the NO by reducing them with acid (usually hydrochloric acid, citric acid
or glacial acetic acid is used). This gives the nitrosonium ion (NO) which then can react with
anions (such as iodine which is commonly used) which then dissociates to give NO, water and
iodine, with the No able to be measured in the chemiluminscence analyser.
Figure 4.4: Reaction equations used to release nitric oxide from other nitrogen compounds
NOz' + 2H+ -> NO* + H2O
NO* + l'+ ONl
2ONl +2NO+lz
As can be seen, this is more difficult than the direct gas measurement and involves more
steps. In addition, all the reagents must be replaced with every sample and extra time required
for signal of the acid and iodine compounds alone. It is very temperature and (clearly) pH
dependent. However, as mentioned above, when correctly performed it remains very sensitive
to NO in small amounts (Zafiriou and McFarland 1980).
4.6.1 Calibration
Machine calibration had to be carried out regularly, and at the time a number of commercial
gas companies offered cylinders with graduated NO concentrations:
o BOC Gases, Surrey Research Park, Guildford, Surrey, UK
o Scott Specialty Gases, Troy, Michigan
o Matheson, East Rutherford, New Jersey
(Modified from our original published chapter (Byrnes, Bush et al. 1996)).
These were prepared by oxidation of ammonia at 5000C over platinum gauze or produced by
passing an electric arc through the air (Braker and Mossman L975).Individual calibration
samples of NO can be prepared chemically either by adding acids to sodium nitrite (NaNOz),
or mixing NOz- and a denitrifying enzyme (Pai, Payne et al. 1987). A preparation of a
saturated NO solution (NO = 3 mM) is needed. Double distilled cold water is bubbled with
103