An elevated concentration of nitric oxide (NO) in alveolar ventilation indicates inflammatory stress within the lung. Trace-gas analysis using mass spectrometers (MS) have been used extensively within the atmospheric community with great success. We present here the first description of time-resolved NO measurement in breath using photoionization MS, providing new capabilities for the medical investigator, such as isotopic tracing.
For NO measurement, we use resonance enhanced multiphoton ionization (REMPI) coupled with a time-of-flight MS with a medium pressure laser ion source. A single male subject breathes NO-free air for several minutes, and then the exhaled breath is monitored for NO.
The ability of REMPI to differentiate among three different isotopomers of NO is demonstrated, and then the concentration profile of NO in exhaled breath is measured. A similar time-dependence concentration is found as observed by previous techniques.
This study presents MPLI-MS as a new technique available for the time-resolved measurement of NO in breath. The resulting system can be made portable and brought into the medical setting using newer-generation, broad-bandwidth lasers. When measuring NO via REMPI, we found a concentration profile in agreement with that of research groups using different techniques (chemiluminescence and LMRS). Sampling the breath from a person without respiratory ailments, we found a dead-space air NO concentration of 20 ppbV and an alveolar ventilation concentration of 5 ppbV. In contrast to the chemical-based technique chemiluminescence, MPLI-MS can also selectively measure isotopically-labeled NO, as demonstrated with REMPI of 14N16O, 15N16O and 14N18O. Further, MPLI-MS can be used to measure other biologically-significant molecules, such as the aldehydes. In forthcoming studies, we will explore the application of MPLI-MS for the measurement of other biologically-significant molecules.
(1) ppbV mixing ratios of NO can be measured on a sub-second time scale, (2) other biologically significant gas molecules can be measured on a similar time scale and (3) since the technique operates optically as well as mass-resolved, isotopomers of NO are discernable, permitting the use of isotopic tracing.
Luke Short, None.