T03_05

Microsublimation as final purification step for ¹⁴C analysis of specific compounds after chromatographic separation

Heusser C¹, Wacker L¹, Eglinton T¹, Welte C¹

¹ETH Zürich, Zürich, Switzerland

With the decrease in sample size requirements for radiocarbon (¹⁴C) analysis by accelerator mass spectrometry (AMS) down to 10 micrograms of carbon or less, measurement of individual source- or process-diagnostic compounds has become feasible. Many key target compounds are amenable to isolation using preparative chromatographic methods such as high-performance liquid chromatography (HPLC) and gas chromatography (GC). However, during compound isolation and other sample pretreatment steps, carbon from external sources can be introduced, which poses a major limitation to precise ¹⁴C dating at very small sample sizes. Here we test the potential of micro-sublimation as an approach for purification of selected compounds after chromatographic separation prior to ¹⁴C analysis. While sublimation is a well-established approach for purification of semi-volatile organic compounds in synthetic and analytical chemistry, commercial sublimation equipment is not designed for the purification of organic compounds in the sub-milligram range, a custom-built micro-sublimation apparatus has been developed, refined and tested. The sublimation characteristics, such as sublimation time, temperature and recoveries will be presented for a range of compound classes (amino acids, n-alkanes, lignin phenols). We will critically discuss the benefits and limitations of using microsublimation as a final cleaning step for compound specific ¹⁴C analysis with special regards to counteract the risk of introducing external carbon.