Direct determination of trace nitrogen dioxide by atmospheric pressure lonization mass spectrometry (APIMS) without conversion to nitric oxide.

The aim of this study was to develop a new method for the determination of NO(2) levels encountered in clinical settings as well as in environmental studies, using a bi-component atmospheric pressure ionization mass spectrometry (APIMS). Hydrogen (1%) diluted in pure argon was ionized by corona discharge in the first ionization component. Fifty ml of the analyte diluted in 250 ml of composite air or carbon dioxide (CO2) was introduced into the second ionization component and analyzed. When composite air was used as the sample carrier gas, NO in the analyte was oxygenated and there was an increase in the NO(2) content from that in the original analyte. However, when CO(2) was used as the sample carrier gas, the level of NO(2) in the analyte could be determined because CO(2) did not change the NO(2) content from that in the original analyte. A calibration curve with good linearity was obtained using the UG-410 APIMS system, with a regression equation of Y(%) = 5.513*10(-2) X (ppb) and a detection limit of 0.9 ppb. Since APIMS detects NO(2) direcdy within its system, the concentration of NO does not need to be measured. This system may be of great help in the accurate detection and determination of the concentration of low levels of NO(2) during inhaled NO therapy.