Particulate nitrogen analytical methods

Ammonia may be present in air in both the vapor and particulate phase as ammonia gas and as ammonium salts. While analytical methods may distinguish between these phases, most standard methods do not. Methods have been developed that determine gaseous ammonia alone or gaseous and particulate forms of ammoniacal nitrogen separately. These methods use filter packs or sampling tubes coated with a selective adsorbent (denuder tube) to separate the phases (Dimmock and Marshall 1986 Knapp et al. 1986 Rapsomanikis et al. 1988). In these methods, gaseous ammonia is trapped by an adsorbent (e.g., citric acid, oxalic acid, phosphoric acid) on a coated filter or denuder tube (Kirchner et al. 1999). In filter methods, errors may arise due to ammonia interactions occurring on the filter and volatilization of retained ammonium salt (Dimmock and Marshall 1986 Rapsomanikis et al. 1988). 

Analytical Methods for Determination of Total Dissolved Nitrogen and Particulate Nitrogen... 

PN is included in the TON, if unfiltered samples are digested by these analytical methods, and it might be determined as difference between TON and DON. However, a more accurate determination of PN requires the analysis of the particulate collected by filtration independently with respect to the determination of dissolved nitrogen forms, as PN often constitutes only a small fraction of the total nitrogen in the natural waters. The digestion of PN collected on filters can be achieved by KD and PO methods, but the most important technique used for this analysis is the HTO method (Figure 14.1). 

---