Luminol-hydrogen peroxide detector for the analysis of nitric oxide in exhaled breath

Nitric oxide (NO) has recently been discovered to be of vital importance in many physiological functions in the human body including neurotransmission, blood clotting, and immune system defense. Exhaled levels of NO can be used to diagnose and monitor asthma and other lung diseases. The measurement of NO in breath may provide a non-invasive means for measuring pulmonary inflammation And for evaluating the effectiveness of medications. In order to expand the research on exhaled NO, there is a need for simple, inexpensive instruments.;A new instrument for quantifying NO in exhaled breath based on a solution-phase chemiluminescence reaction with luminol and hydrogen peroxide is described here. The instrument design makes use of a translucent hollow fiber module as a gas-liquid chemiluminescence cell. The new chemiluminescence method was originally investigated for direct detection of NO, but it was discovered to have little sensitivity to NO. Instead, the technique was extremely useful in detecting trace amounts of nitrogen dioxide (NO2). Therefore, a new approach for NO detection based on oxidation of NO to NO2 was developed. Chromium trioxide (CrO3) coated on an inert substance was found to be a suitable oxidizing agent for NO to NO2 conversion. Exhaled concentrations of carbon dioxide resulted in a significant interference in the measurement of NO. The CO2 interference was minimized either by adding an ascarite scrubber in the air stream or by adding carbonic anhydrase to the luminol solution. The detection limit of the instrument was found to be 0.5 ppbv NO with a S/N = 3, and the response time was ∼2 seconds. The results of NO measurements in exhaled breath were compared to the results obtained with a NO + ozone chemiluminescence analyzer. The NO concentrations measured with both instruments were in good agreement and were found to be in the range 5.0--23.5 ppbv for healthy individuals without asthma. Individuals with asthma or a respiratory infection exhaled NO concentrations in the range 40.0--80.0 ppbv.