Progress in automated extraction and purification of in situ 14C from quartz: Results from the Purdue in situ 14C laboratory

Abstract

Current extraction methods for in situ 14 C from quartz [e.g., 1, 2, 3] are time-consuming and 25 repetitive, making them an attractive target for automation. We report on the status of in situ 14 C 26 extraction and purification systems originally automated at the University of Arizona that have 27 now been reconstructed and upgraded at the Purdue Rare Isotope Measurement Laboratory 28 (PRIME Lab). The Purdue in situ 14 C laboratory builds on the flow-through extraction system 29 design of Pigati et al. [2], automating most of the procedure by retrofitting existing valves with 30 external servo-controlled actuators, regulating the pressure of research purity O 2 inside the 31 furnace tube via a PID-based pressure controller in concert with an inlet mass flow controller, 32 and installing an automated liquid N 2 distribution system, all driven by LabView ® software. A 33

Isolation of quartz for cosmogenic in situ <sup>14</sup>C analysis

“…We hypothesise that, as an oxidiser, HNO 3 is key in the decomposi- tion of laurylamine. Before carbon is extracted from aliquots, quartz is leached in 50 % v/v HNO 3 for 30 min in an unheated ultrasonic bath (Lifton et al, 2001;Goehring et al, 2019). This is important to note because it is apparent that this additional leach with strong HNO 3 is not sufficient alone to remove contaminant 14 C and highlights the importance of HF as well as HNO 3 in the etching procedure and their role in the removal of contamination.…”

Isolation of quartz for cosmogenic in situ <sup>14</sup>C analysis

“…We hypothesise that, as an oxidiser, HNO3 is key in the decomposition of laurylamine. Before carbon is extracted from aliquots, quartz is etched for 30 minutes in 220 50 % HNO3 (Lifton et al, 2001;. This is important to note because it is apparent that this additional etch with strong HNO3 is not sufficient alone to remove contaminant 14 C and highlights the importance of HF as well as HNO3 in the etching procedure and their role in the removal of contamination.…”

“…The fact that the 14 C concentration increase from laurylamine is of the same order of magnitude as that of typical in 230 situ 14 C measurements is of great concern and highlights the need for a standardised procedure to eliminate contamination from the quartz isolation process. Carbon introduced by laurylamine is evidently persisting through a 500 °C bake, the first stage of extracting 14 C from quartz with the TU-CEGS and in other in situ 14 C laboratories (e.g., Hippe et al, 2013;Lifton et al, 2015;Lamp et al, 2019). The 500 °C bake was previously shown to remove contaminant 14 C (Lifton et al, 2001), though this was from sample handling and the atmosphere and pre-dates the implementation of froth floatation 235 for quartz separation.…”

“…Carbon introduced by laurylamine is evidently persisting through a 500 °C bake, the first stage of extracting 14 C from quartz with the TU-CEGS and in other in situ 14 C laboratories (e.g., Hippe et al, 2013;Lifton et al, 2015;Lamp et al, 2019). The 500 °C bake was previously shown to remove contaminant 14 C (Lifton et al, 2001), though this was from sample handling and the atmosphere and pre-dates the implementation of froth floatation 235 for quartz separation. We suspect that the observed contamination is sourced from laurylamine residing within microfractures of quartz grains, which may explain why the contamination is able to persist through the 500 °C bake and possibly accounts for differences in the degrees of contamination between previously analysed samples and those as part of this study due to differences in the quartz grain characteristics.…”

“…We isolated quartz from a whole rock sample using five different methods in order to investigate the cause of contamination. The sample selected for this purpose is Caledonian trondhjemite bedrock (Ragnhildstveit et al, 1998) from Utsira, Norway. The sample contains significant feldspar, mica and quartz, making it ideal for use with froth flotation.…”