Analysis and identification of chemical warfare agent (CWA) degradation products presents notable challenges, primarily due to the extensive quantity of the compounds involved, surpassing millions. A majority CWA-related compounds are characterized by low volatility, making liquid chromatography high-resolution mass spectrometry (LC-HRMS) a suitable analysis method. Untargeted screening is promising technique for swift analysis of complex samples, without specific preselection of any compound. In this project, an LC-HRMS method was developed for separation and analysis of CWA-related compounds, using a Dionex 3000 UHPLC-system and a Bruker Impact qTOF mass spectrometer. The method was able to separate most compounds, including several isomers, from each other, and can be used for analysing samples with a large variety of unknown CWA-related compounds. Secondly, a MSspectra library was created for 115 CWA-related compounds. The spectra were obtained by alternating between full MS-scan and broad-band collision induced dissociation (bbCID). Four MS-spectra were added for each compound, one containing the precursor ion spectra (the full MS-scan) and three containing the product ion spectra when using the collision energies 10 eV, 20 eV and 30 eV. While not all compounds could be uniquely identified when screening towards the library, particularly when distinguishing certain isomers from one another, this resource can still be highly valuable for aiding characterization for a wide range of CWA-related compounds. Additionally, prior to adding the spectra to the library, an analysis of all fragment ions was performed and the most plausible structures were recorded in the database. Apart from the library serving as a useful screening tool, this knowledge can prove valuable for future identification of unknown CWA-related compounds. The third part of the project was to optimize the untargeted screening method for CWArelated compounds. A water sample containing 14 CWA-related compounds was analysed when varying the settings of the untargeted screening in the program Bruker Compass DataAnalysis. The new settings, almost exclusively, improved the screening and identification of the compounds. The usefulness and accuracy of the method was evaluated by analysing four different concentrations of a mixture, containing four alkylphosphonic acids, in four different matrices, one water and three soil matrices. The results showed that it was possible to identify several compounds when no visible peaks in the total ion chromatogram were present. This represents an important step for LC-MS analysis in general, since this technique can detect certain compounds that otherwise likely would have been missed when using manual integration.