A new continuous flow isotope ratio mass spectrometry system for the analysis of δ²H, δ¹⁷O and δ¹⁸O of small (120 μg) water samples in atmospheric applications

Abstract

A new continuous-flow system for the analysis of the complete stable isotopic composition of water vapor has been developed. The sample size is reduced to only 120 microg (identical with 120 nL of liquid substance) of water, yielding precisions of about 0.7, 1.3 and 7 per thousand for delta17O, delta18O and delta2H, respectively. The total time for the analysis of a sample is about 150 min including purging times. Oxidized steel surfaces can be a source of memory effects which can be corrected for. The system is predestined for atmospheric applications in the tropopause region, as the sample can be directly introduced into the system from a cryogenic trap.

High-precision isotope measurements of H<sub>2</sub><sup>16</sup>O, H<sub>2</sub><sup>17</sup>O, H<sub>2</sub><sup>18</sup>O, and the Δ <sup>17</sup>O-anomaly of water vapor in the southern lowermost stratosphere

“…The details of the instrumental setup are described elsewhere (Franz and Röckmann, 2004;Franz, 2005), so that only a brief overview will be given here.…”

“…From the time-series of the aliquots, the machine-response of the sample is determined as described in Franz and Röckmann (2004). Since the machine response is not the true isotopic composition of the sample, a calibration is mandatory.…”

“…Typical 1σ errors in δ 18 O are about 2−3‰, and 1.5−2‰ in δ 17 O. However, due to a very tight correlation between individual samples, 17 O can be determined with precisions between 0.3 and 2‰, depending on sample amount (Franz, 2005;Franz and Röckmann, 2004).…”

“…Associated with the large size of the traps are large surface areas, which are hard to clean from adsorbed water molecules, and therefore display significant memory effects (Zahn, 1995;Zahn et al, 1998). The sampler used in this work makes use of an online method described in Franz and Röckmann (2004), which reduces the required sample amount to less than 100 µg. The corresponding traps are small (∼150 ml) and can be purged easily, thus minimizing memory effects.…”

A water isotope (2H, 17O, and 18O) spectrometer based on optical feedback cavity-enhanced absorption for in situ airborne applications

“…Analytical errors are reported as ∼ 50 ‰ for all isotopes, and larger at low water concentration (< 10 ppmv). Franz and Röckmann [24] used a small-volume whole-air sampler in combination with a modified small-sample isotope ratio mass spectrometry (IRMS) analysis procedure [25] to obtain a precision of ∼ 2 ‰ for the oxygen isotope ratio measurements. However, due to a strong correlation between the individual measurements, the 17 O anomaly, defined as 18 O, could be determined with a precision of 0.3 to 2 ‰, depending on the sample size.…”