12 May 2023
 | 12 May 2023
Status: this preprint is open for discussion.

Technical note: Studying Li-metaborate fluxes and low-temperature combustion/high-temperature extraction systematics with a new, fully automated in situ cosmogenic 14C processing system at PRIME Lab

Nathaniel Lifton, Jim Wilson, and Allie Koester

Abstract. Extraction procedures for in situ cosmogenic 14C (in situ 14C) from quartz require quantitative isotopic yields while maintaining scrupulous isolation from atmospheric/organic 14C. These time- and labor-intensive procedures are ripe for automation; unfortunately, our original automated in situ 14C extraction and purification systems, reconfigured and retrofitted from our original systems at the University of Arizona, proved less reliable than hoped. We therefore installed a fully automated stainless-steel system (except for specific glass or fused-quartz components) incorporating more reliable valves and improved actuator designs, along with a more robust liquid nitrogen distribution system. As with earlier versions, the new system uses a degassed Li-metaborate (LiBO2) flux to dissolve the quartz sample in an ultra-high-purity oxygen atmosphere, after a lower-temperature combustion step to remove atmospheric/organic 14C.

We compared single-use high-purity Al2O3 vs. reusable 90 %Pt/10 %Rh (Pt/Rh) sample combustion boats. The Pt/Rh boats heat more evenly than the Al2O3, reducing procedural blank levels and variability for a given LiBO2 flux. This lower blank variability also allowed us to trace progressively increasing blanks to specific batches of fluxes from our original manufacturer. Switching to a new manufacturer returned our blanks to consistently low levels on the order of (3.4 ± 0.9) x 104 14C atoms.

We also analyzed the CRONUS-A intercomparison material to investigate sensitivity of extracted 14C concentrations to the temperature and duration of the combustion and extraction steps. Results indicate that 1-hr combustion steps at either 500 or 600 °C yield results consistent with the consensus value of Jull et al. (2015), while 2 hr at 600 °C results in loss of ca. 9 % of the high-temperature 14C inventory. Results for 3 hr extractions at temperatures ranging from 1050 °C to 1120 °C and 4.5 hr at 1000 °C yielded similar results that agreed with the nominal value as well as with published results from most laboratories. On the other hand, an extraction for 3 hr at 1000 °C was judged to be incomplete due to a significantly lower measured concentration. Based on these results, our preferred technique is now combustion for 1 hr at 500 °C followed by a 3 hr extraction at 1050 °C. Initial analyses of the CoQtz-N intercomparison material at our lab yielded concentrations ca. 60 % less than those of CRONUS-A, but more analyses of this material from this and other labs are clearly needed to establish a consensus value.

Nathaniel Lifton et al.

Status: open (until 23 Jun 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Nathaniel Lifton et al.

Nathaniel Lifton et al.


Total article views: 127 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
95 28 4 127 2 1
  • HTML: 95
  • PDF: 28
  • XML: 4
  • Total: 127
  • BibTeX: 2
  • EndNote: 1
Views and downloads (calculated since 12 May 2023)
Cumulative views and downloads (calculated since 12 May 2023)

Viewed (geographical distribution)

Total article views: 128 (including HTML, PDF, and XML) Thereof 128 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 04 Jun 2023
Short summary
We describe a new, fully automated extraction system for in situ 14C at PRIME Lab that incorporates more reliable components and designs than our original systems. We use a LiBO2 flux to dissolve a quartz sample in oxygen, after removing contaminant 14C with a lower-temperature combustion step. Experiments with new Pt/Rh sample boats demonstrated reduced procedural blanks, and analyses of well-characterized intercomparison materials tested effects of process variables on 14C yields.