A simple and cost-effective sample preparation and storage method for stable isotope analysis of atmospheric CO2 for GasBench II/continuous flow isotope ratio mass spectrometry.

Abstract

The stable isotope compositions of atmospheric CO2 can provide useful insight into various geochemical processes and carbon cycles on Earth, which is critical for understanding of Earth's changing climate. Here, we present a simple and cost-effective analytical method for the collection and measurement of carbon and oxygen isotope compositions of atmospheric CO2. Air samples of ~150 mL were collected individually or collectively using our simple active air collection system and then extracted on a vacuum purification line to remove noncondensable gases and atmospheric water vapor. The efficiency of removing atmospheric water vapor was tested by using a magnesium perchlorate desiccant trap and a dry ice/ethanol trap. Lastly, a "J-Cut tube sealing/cracking method" was developed to store and transfer purified atmospheric CO2 to the GasBench II and CF-IRMS system for δ13C and δ18O measurements. The collective active air collection method combined with the full sample air extraction method for a 3-min transfer time or "Full 3m TE" yields the best analytical precision of 0.07‰ (δ13C) and 0.04‰ (δ18O). Removing atmospheric water vapor from air samples is not necessary for δ13C, but essential for δ18O measurements. The J-Cut tube sealing/cracking method shows a near 100% effectiveness for the storage and transfer of atmospheric or any CO2. A simple and cost-effect method was developed for the collection, purification, storage, and isotopic analysis of indoor/outdoor atmospheric CO2 samples for general users. This method utilizes a popular headspace gas sample preparation system for CF-IRMS and an easy-to-build vacuum purification line without involving complex and high-cost devices for the preparation of atmospheric CO2.