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  • Technical note: Studying lithium metaborate fluxes and extraction protocols with a new, fully automated in situ cosmogenic 14 C processing system at PRIME Lab
Title: Technical note: Studying lithium metaborate fluxes and extraction protocols with a new, fully automated in situ cosmogenic 14 C processing system at PRIME Lab
Abstract. Extraction procedures for in situ cosmogenic 14C (in situ 14C) fromquartz require quantitative isotopic yields while maintaining scrupulousisolation from atmospheric and organic 14C. These time- and labor-intensiveprocedures are ripe for automation; unfortunately, our original automatedin situ 14C extraction and purification systems, reconfigured and retrofittedfrom our original systems at the University of Arizona, proved less reliablethan hoped. We therefore installed a fully automated stainless-steel system(except for specific borosilicate glass or fused-silica components)incorporating more reliable valves and improved actuator designs, along witha more robust liquid nitrogen distribution system. As with earlier versions,the new system uses a degassed lithium metaborate (LiBO2) flux to dissolvethe quartz sample in an ultra-high-purity oxygen atmosphere, after alower-temperature combustion step to remove atmospheric and organic 14C. We compared single-use high-purity Al2O3 against reusable90 %Pt / 10 %Rh (Pt/Rh) sample combustion boats. The Pt/Rh boats heat moreevenly than the Al2O3, reducing procedural blank levels andvariability for a given LiBO2 flux. This lower blank variability alsoallowed us to trace progressively increasing blanks to specific batches offluxes from our original manufacturer. Switching to a new manufacturerreturned our blanks to consistently low levels on the order of (3.4 ± 0.9) × 104 14C atoms. We also analyzed the CRONUS-A intercomparison material to investigatesensitivity of extracted 14C concentrations to the temperature andduration of the combustion and extraction steps. Results indicate that 1 hcombustion steps at either 500 or 600 ∘C yield results consistentwith the consensus value of Jull et al. (2015), while 2 hat 600 ∘C results in loss of ca. 9 % of the high-temperature14C inventory. Results for 3 h extractions at temperatures rangingfrom 1050 to 1120 ∘C and 4.5 h at 1000 ∘Cyielded similar results that agreed with the nominal value andpublished results from most laboratories. On the other hand, an extractionfor 3 h at 1000 ∘C was judged to be incomplete due to asignificantly lower measured concentration. Based on these results, ourpreferred technique is now combustion for 1 h at 500 ∘C followedby a 3 h extraction at 1050 ∘C. Initial analyses of the CoQtz-Nintercomparison material at our lab yielded concentrations ca. 60 % lowerthan those of CRONUS-A, but more analyses of this material from this andother labs are clearly needed to establish a consensus value.  more » « less
Award ID(s):
2300559
PAR ID:
10515246
Author(s) / Creator(s):
; ;
Publisher / Repository:
Copernicus Publications
Date Published:
Journal Name:
Geochronology
Volume:
5
Issue:
2
ISSN:
2628-3719
Page Range / eLocation ID:
361 to 375
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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