Plastic pollution has become a globally emerging problem leading to the formation of persisting microplastics (MPs). Electrothermal vaporization coupled with inductively coupled plasma-mass spectrometry (ETV/ICP-MS) is a promising tool for a fast and comprehensive assessment of the MP pollution situation in environmental samples. In this study, a new mass-based approach has been developed for the sum parameter analysis of MPs in soil via the ¹³C isotope. Quantification was achieved through an external gas calibration with carbon dioxide. Furthermore, the potential of polymer heteroatoms and contaminants was evaluated for the sensitive MP detection in carbon-rich matrices.