A universal approach to alpha-cellulose extraction for radiocarbon analysis of 14C-free to post-bomb ages

In order to expand our in-house capabilities for tree-ring 14C measurements in support of atmospheric 14C reconstruction research, we designed a very versatile and inclusive procedure to produce high-quality α-cellulose homogenized extracts. The procedure can be easily scaled up or down (≤10 to 40 samples) and/or modified on demand (chemical steps can be easily adjusted to sample requirements as well, e.g., increased or diminished, according to the amount of available material and/or contaminants to be removed). Procedure setups are straightforward, and all products and instruments required are off-the-shelf. One to three days may be used to extract chipped wood to α-cellulose homogenized fibers that can be further used by high-precision 14C accelerator mass spectrometry (AMS) analysis. The full procedure, which includes recommendations for wood reduction to chips, chemical treatment, and 14C-AMS sample processing, measurements and data handling was tested on over 110 wood samples from post-bomb 1950AD to 14C limit. Radiocarbon results were in the order of 0.29% or better, based on replication and regardless of the age group studied. Best background was in the order of 54 kyrs BP, without any type of background correction. Fourier transform infrared (FTIR) analysis was used as a characterizing tool to confirm the removal of unwanted carbon compounds during the production of α-cellulose extracts. For those analysis, we chose woods that are normally rich in resinous and parenchymatous structures. Results confirmed that our protocol produces pure α-cellulose extracts for 14C analysis, and therefore this procedure can be safely applied to atmospheric 14C reconstructions at pantropical regions.