Comparison of methods to determine triple oxygen isotope composition of N₂O

Abstract

The use of microwave-induced plasma in a corundum tube yields best results for Δ(17) O measurement on N2 O gas samples.

Automated system measuring triple oxygen and nitrogen isotope ratios in nitrate using the bacterial method and N2O decomposition by microwave discharge

“…As the size of the dependency of the measurement fits a ln regression (Fig. ), as was also observed by Dyckmans et al for the Δ 17 O value of the MIP reaction to produce O 2 from N 2 O, we assume that exchange of sample oxygen with oxygen present in the microwave discharge unit is the most likely reason for this observation.…”

“…This size dependency might result from the analytical blank, isotopic exchange during the bacterial denitrification reaction, or oxygen isotopic exchange between the sample oxygen and oxygen present in the microwave discharge unit . As the size of the dependency of the measurement fits a ln regression (Fig.…”

“…Consequently, using 100 nmol nitrate, the SDs of the measurements for our system were estimated, respectively, as 0.5, 0.3, and 0.1‰ for the δ 18 O, Δ 17 O, and δ 15 N values. In comparison with our previous system using MIP, the precision of the measurement was improved because of the temperature stability of the tube, the fixed sample size obtained by automation, and the purification of N 2 O by GC before the microwave discharge, as described above. This level of precision of this measurement system is not inferior to that of other systems using a gold tube and gold wire …”

“…; Saint‐Gobain KK, Tokyo, Japan) that passes through the cavity. The corundum tube has been reported to have better heat stability than a quartz tube . The MIP is generated by ignition by tesla coils with reduced inner pressure of the corundum tube via vacuum pumping (Fig.…”

“…An alternative on‐line system measuring the Δ 17 O value using decomposition of N 2 O by microwave‐induced plasma (MIP) was also described in an earlier report . For the latter method that used microwave discharge of N 2 O, an updated method using a corundum tube instead of a quartz tube has also been reported . To date, the decomposition of N 2 O by MIP has been applied for only δ 18 O and Δ 17 O measurements, but this method in principle can be used to measure δ 15 N values during the same analytical run.…”