Automated and rapid online determination of 15N abundance and concentration of ammonium, nitrite, or nitrate in aqueous samples by the SPINMAS technique.

On the basis of the principle of reaction continuous-flow quadrupole mass spectrometry, an automated sample preparation unit for inorganic nitrogen (SPIN) species was developed and coupled to a quadrupole Mass Spectrometer (MAS). The SPINMAS technique was designed for an automated, sensitive, and rapid determination of 15N abundance and concentration of a wide variety of N-species involved in nitrogen cycling (e.g. NH4+, NO3-, NH2OH etc.). In this paper, the SPINMAS technique is evaluated with regard to the determination of 15N abundance and concentration of the most fundamental inorganic nitrogen compounds in ecosystems such as NH4+, NO2-, and NO3-. The presented paper describes the newly developed system in detail and demonstrates the general applicability of the system. For a precise determination of 15N abundance and concentration, a minimum total N-amount of 10 microg NH4+ - N, 0.03 microg NO2- - N, or 0.3 microg NO3- - N has to be supplied. Currently, the SPINMAS technique represents the most rapid and only fully automated all-round method for a simultaneous determination of 15N abundance and total N-amount of NH4+, NO2-, or NO3- in aqueous samples.

A 15N-aided artificial atmosphere gas flow technique for online determination of soil N2 release using the zeolite Köstrolith SX6.

N2 is one of the major gaseous nitrogen compounds released by soils due to N-transformation processes. Since it is also the major constituent of the earth's atmosphere (78.08% vol.), the determination of soil N2 release is still one of the main methodological challenges with respect to a complete evaluation of the gaseous N-loss of soils. Commonly used approaches are based either on a C2H2 inhibition technique, an artificial atmosphere or a 15N-tracer technique, and are designed either as closed systems (non-steady state) or gas flow systems (steady state). The intention of this work has been to upgrade the current gas flow technique using an artificial atmosphere for a 15N-aided determination of the soil N2 release simultaneously with N2O. A 15N-aided artificial atmosphere gas flow approach has been developed, which allows a simultaneous online determination of N2 as well as N2O fluxes from an open soil system (steady state). Fluxes of both gases can be determined continuously over long incubation periods and with high sampling frequency. The N2 selective molecular sieve Köstrolith SX6 was tested successfully for the first time for dinitrogen collection. The presented paper mainly focuses on N2 flux determination. For validation purposes soil aggregates of a Haplic Phaeozem were incubated under aerobic (21 and 6 vol.% O2) and anaerobic conditions. Significant amounts of N2 were released only during anaerobic incubation (0.4 and 640.2 pmol N2 h(-1) g(-1) dry soil). However, some N2 formation also occurred during aerobic incubation. It was also found that, during ongoing denitrification, introduced [NO3]- will be more strongly delivered to microorganisms than the original soil [NO3]-.