Microgram level radiocarbon (¹⁴C) determination
on carbonaceous particles in ice

T.M. Jenk, S. Szidat, M. Schwikowski, H.W. Gäggeler, L. Wacker, H.-A. Synal, M. Saurer
Nuclear Instruments and Methods in Physics Research B 259 (2007) 518–525

ABSTRACT.
In climate research the interest on carbonaceous particles has increased over the last years because of their influence on the radiation balance of the earth. Nevertheless, there is a paucity of available data regarding their concentrations and sources in the past. Such data
would be important for a better understanding of their effects and for estimating their influence on future climate. Here, a technique is described to extract carbonaceous particles from ice core samples with subsequent separation of the two main constituents into organic
carbon (OC) and elemental carbon (EC) for analysis of their concentrations in the past. This is combined with further analysis of OC and EC ¹⁴C/¹²C ratios by accelerator mass spectrometry (AMS), what can be used for source apportionment studies of past emissions. We further present how ¹⁴C analysis of the OC fraction could be used in the future to date any ice core extracted from a high-elevation glacier. Described sample preparation steps to final analysis include the combustion of micrograms of water-insoluble carbonaceous
particles, primary collected by filtration of melted ice samples, the graphitisation of the obtained CO₂ to solid AMS target material and final AMS measurements. Possible fractionation processes were investigated for quality assurance. Procedural blanks were reproducible and resulted in carbon masses of 1.3 ± 0.6 lg OC and 0.3 ± 0.1 lg EC per filter. The determined fraction of modern carbon (ƒ_M) for the OC blank was 0.61 ± 0.13. The analysis of processed IAEA-C6 and IAEA-C7 reference material resulted in ƒ_M = 1.521 ± 0.011 and δ¹³C = 10.85 ± 0.19‰, and f_M = 0.505 ± 0.011 and δ¹³C =14.21 ± 0.19‰, respectively, in agreement with consensus values. Initial carbon contents were thereby recovered with an average yield of 93%.