This was the first experiment designed to enrich an atmospheric sample
in nitrogen and noble gases, particularly argon. A series of 9 cycles
scrubbed active gases and enriched the sample in the target species.
Background for nitrogen and argon was subtracted by assuming that an
initial value measured prior to introduction of atmospheric gas into
the manifold followed the same trend during atmospheric analysis as a
tracer mass (m/z 39) that did not contain atmospheric gas. Initial
background values were computed by averaging peak areas at each m/z for
the last 10 scans of the first background region. Background for krypton
was assumed to be constant during the run, taken as the average over the
last 10 scans of the first background region.
Argon isotope ratios were computed from fractional scan peak areas at
m/z 36 and 38, at each m/z +/- 0.4. Nitrogen isotope ratios were
computed from m/z 14 and 14.5, from each m/z +/- 0.1.