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  • A sealed‐tube method for offline δ 13 C analysis of CO 2 via a Gas Bench II continuous‐flow isotope ratio mass spectrometer
Title: A sealed‐tube method for offline δ 13 C analysis of CO 2 via a Gas Bench II continuous‐flow isotope ratio mass spectrometer
Rationale

The isotopic measurement of environmental sample CO2via isotope ratio mass spectrometry (IRMS) can present many analytical challenges. In many offline applications, exceedingly few samples can be prepared per day. In such applications, long‐term storage (months) of sample CO2is desirable, in order to accumulate enough samples to warrant a day of isotopic measurements. Conversely, traditional sample tube cracker systems for dual‐inlet IRMS offer a capacity for only 6–8 tubes and thus limit throughput. Here we present a simple method to alleviate these concerns using a Gas Bench II gas handling device coupled with continuous‐flow IRMS.

 Methods

Sample preparation entails the cryogenic purification and quantification of CO2on a vacuum line. Sample CO2splits are expanded from a known volume to several sample ports and allowed to isotopically equilibrate (homogenize). Equilibrated CO2splits are frozen into 3 mm outer diameter Pyrex break‐seals and sealed under vacuum with a torch to a length of 5.5 cm. Sample break‐seals are scored, placed into 12 mL Labco Exetainer®vials, purged with ultrahigh‐purity helium, cracked inside the capped helium‐flushed vials and subsequently measured via a Gas Bench equipped IRMS instrument using a CTC Analytics PAL autosampler.

 Results

Our δ13C results from NIST and internal isotopic standards, measured over a time period of several years, indicate that the sealed‐tube method produces accurate δ13C values to a precision of ±0.1‰ for samples containing 10–35 μgC. The tube cracking technique within Exetainer vials has been optimized over a period of 10 years, resulting in decreased sample failure rates from 5–10% to <1%.

 Conclusions

This technique offers an alternative method for δ13C analyses of CO2where offline isolation and long‐term storage are desired. The method features a much higher sample throughput than traditional dual‐inlet IRMS cracker setups at similar precision (±0.1‰).

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NSF-PAR ID:
10452145
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Rapid Communications in Mass Spectrometry
Volume:
35
Issue:
7
ISSN:
0951-4198
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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