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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
Author(s) -
Walker Brett D.,
Beaupré Steven R.,
Griffin Sheila,
Walker Jennifer,
Druffel Ellen,
Xu Xiaomei
Publication year - 2021
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.9040
Subject(s) - chemistry , analytical chemistry (journal) , isotope ratio mass spectrometry , mass spectrometry , sample preparation , helium , volumetric flow rate , tube (container) , volume (thermodynamics) , chromatography , materials science , physics , composite material , organic chemistry , quantum mechanics
Rationale The isotopic measurement of environmental sample CO 2 via 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 CO 2 is 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 CO 2 on a vacuum line. Sample CO 2 splits are expanded from a known volume to several sample ports and allowed to isotopically equilibrate (homogenize). Equilibrated CO 2 splits 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 δ 13 C results from NIST and internal isotopic standards, measured over a time period of several years, indicate that the sealed‐tube method produces accurate δ 13 C 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 δ 13 C analyses of CO 2 where 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‰).