Understanding how carbon moves and changes in soil is key to addressing climate change and improving soil health. Researchers often use carbon-13 (¹³C) to trace where carbon goes in the environment. However, it’s been difficult and expensive to measure ¹³C in liquid soil extracts, where carbon is dissolved in water or salt solution. Current methods require highly specialized equipment or complicated steps that can lead to errors. In this study, we developed a simpler and more affordable method to measure ¹³C in soil extracts. Our technique works with commonly used salt solutions, reduces sample processing, and only requires a gas-phase analyzer. We tested this method and found it recovered more than 95% of the carbon, even at low concentrations, and could accurately detect different levels of ¹³C.