Characteristics of a novel alkali flame ionization detector as an air sensor for volatile organo-nitrogen compounds

A novel alkali flame ionization detector (AFID) is introduced and characterized for use as an air sensor (i.e., without chromatographic separation) for organo-nitrogen compounds. Using a planar channeled quartz design, a simple, lightweight architecture for the portable device is presented, which yields sensitive and selective response toward nitrogen-containing analytes. For instance, the AFID sensor offers a detection limit of 30 pg N/s and a selectivity for nitrogen response over carbon of nearly two orders of magnitude. Further, nitrogen response is linear over the 1000-fold range of concentrations investigated. Relative to a flame photometric detector (FPD) device also used in a sensor mode, the AFID is observed to provide 100 times greater S/N values for nitrogen analytes with a nitrogen-to-carbon selectivity that is about 15 times larger. When using the AFID and FPD sensors in tandem, it is found that the response ratio of the simultaneous signals generated by each produces characteristic values that more clearly identify the presence or absence of nitrogen in unknown analytes. The AFID sensor was used to detect organo-nitrogen analytes in several samples, and results indicate that it could be a useful approach for portable air sensing of nitrogen compounds.