A rapid method for preparing low volume CH4 and CO2 gas samples for 14C AMS analysis

14 C measurements of CH 4 in environmental samples (e.g. soil gas, lake water, gas hydrates) can advance understanding of C cycling in terrestrial and marine systems. The measurements are particularly useful for detecting the release of old C from climate sensitive environments such as peatlands and hydrate fields. However, because 14 C CH 4 measurements tend to be complex and time consuming, they are uncommon. Here, we describe a novel vacuum line system for the preparation of CH 4 and CO 2 from environmental samples for 14 C analysis using accelerator mass spectrometry (AMS). The vacuum line is a flow-through system that allows rapid preparation of samples (1 h for CH 4 and CO 2 , 30 min for CH 4 alone), complete separation of CH 4 and CO 2 and is an easy addition to multipurpose CO 2 vacuum lines already in use. We evaluated the line using CH 4 and CO 2 standards with different 14 C content. For CH 4 and CO 2 , respectively, the total line blank was 0.4 ± 0.2 and 1.4 ± 0.6 μg C, the 14 C background 51.1 ± 1.2 and 48.4 ± 1.5 kyr and the precision (based on pooled standard deviation) 0.9‰ and 1.3‰. The line was designed for sample volumes of ca. 180 ml containing 0.5–1% CH 4 and CO 2 , but can be adjusted to handle lower concentration and larger volume samples. This rapid and convenient method for the preparation of CH 4 and CO 2 in environmental samples for 14 C AMS analysis should provide more opportunities for the use of 14 C CH 4 measurements in C cycle studies.