N. Binding et al., NO chemiluminescence in exhaled air: interference of compounds from endogenous or exogenous sources, EUR RESP J, 16(3), 2000, pp. 499-503
Nitric oxide determination in exhaled air using chemiluminescence analysers
is increasingly used, but may be affected by various other components of t
he air sample. The influence of several compounds originating from endogeno
us or exogenous sources on NO readings has been studied.
Defined amounts of water vapour, carbon dioxide, acetone, heptane, acetonit
rile, oxygen, nitrous oxide and enflurane were added to air samples with NO
concentrations 0-250 parts per billion.
Marked and significant decreases in NO readings, which strongly depend on t
he concentration of the respective interfering compound, were found for wat
er vapour (0.155% per 1% relative humidity), carbon dioxide (1.97% per 1% C
O2 volume/volume (v/v)) and nitrous oxide (0.608% per 1% v/v N2O). While ac
etone in concentrations up to 8.5% v/v had no measurable effect on NO readi
ngs, heptane and acetonitrile led to marked decreases. Oxygen in concentrat
ions of up to 95% (viv) had no effect on NO determination. NO readings were
markedly decreased by >10% per 1% (v/v) of the anaesthetic enflurane. Howe
ver, due to large variations in NO values, these decreases were not statist
ically significant. Furthermore, enflurane reacted,vith the molybdenum conv
erter of the NO, analyser in use, resulting in major damage to the instrume
nt.
Eliminating, or at least considering, interferences by compounds present in
exhaled air is an urgent prerequisite for reliable and precise nitric oxid
e determination.