¹⁴C Blank Assessment in Small-Scale Compound-Specific Radiocarbon Analysis of Lipid Biomarkers and Lignin Phenols

Abstract

Compound-specific radiocarbon (14C) dating often requires working with small samples of < 100 µg carbon (µgC). This makes the radiocarbon dates of biomarker compounds very sensitive to biases caused by extraneous carbon of unknown composition, a procedural blank, which is introduced to the samples during the steps necessary to prepare a sample for radiocarbon analysis by accelerator mass spectrometry (i.e., isolating single compounds from a heterogeneous mixture, combustion, gas purification and graphitization). Reporting accurate radiocarbon dates thus requires a correction for the procedural blank. We present our approach to assess the fraction modern carbon (F14C) and the mass of the procedural blanks introduced during the preparation procedures of lipid biomarkers (i.e. n-alkanoic acids) and lignin phenols. We isolated differently sized aliquots (6–151 µgC) of n-alkanoic acids and lignin phenols obtained from standard materials with known F14C values. Each compound class was extracted from two standard materials (one fossil, one modern) and purified using the same procedures as for natural samples of unknown F14C. There is an inverse linear relationship between the measured F14C values of the processed aliquots and their mass, which suggests constant contamination during processing of individual samples. We use Bayesian methods to fit linear regression lines between F14C and 1/mass for the fossil and modern standards. The intersection points of these lines are used to infer F14Cblank and mblank and their associated uncertainties. We estimate 4.88 ± 0.69 μgC of procedural blank with F14C of 0.714 ± 0.077 for n-alkanoic acids, and 0.90 ± 0.23 μgC of procedural blank with F14C of 0.813 ± 0.155 for lignin phenols. These F14Cblank and mblank can be used to correct AMS results of lipid and lignin samples by isotopic mass balance. This method may serve as a standardized procedure for blank assessment in small-scale radiocarbon analysis.

Transformation of dissolved organic matter by two Indo‐Pacific sponges

“…Radiocarbon data were normalized and blank corrected against standard (NIST Oxalic Acid II; NIST SRM4990C) and blank ( 14 C free) CO 2 gas. Furthermore, the tin capsule blank was determined and corrected for, following the protocol described by Sun et al (2020).…”

Estimating Bioturbation From Replicated Small‐Sample Radiocarbon Ages

“…Blank correction of foraminifera samples was performed against sample-size matched Eemian-age foraminifera from GeoB 3316-1. Blanks were processed and correction performed according to a procedure in Sun et al (2020). Radiocarbon dating of the bulk samples from core SO213-84-2 was carried out at NOSAMS, Woods Hole Oceanographic Institution and Keck Carbon Cycle AMS Laboratory, University of California, Irvine.…”

Deglacial release of petrogenic and permafrost carbon from the Canadian Arctic impacting the carbon cycle

“…Blank correction of compound-specific samples requires careful determination of F 14 C of the blank and the size of blank. For this purpose, radiocarbon analyses of in-house reference samples from 14 C-free Eocene Messel Shale (F 14 C OC = 0) and modern apple peel (F 14 C OC = 1.029 ± 0.001) processed in the same way as the compound-specific samples were conducted to determine the F 14 C and mass of blank, following the method of Sun et al 65 . All radiocarbon data were corrected for the procedural blank and, to remove the contribution of the methyl group added during the derivatization process, a methyl correction was further performed through isotopic mass balance.…”