During events involving the use of toxic chemical agents, it is critical to obtain as much information as possible about the history of the agent. Chemical attribution signatures can be used to provide an evidentiary link between the use of a given chemical threat agent and its origin to support forensic investigations [1,2]. Numerous factors like low concentrations, sample ageing and complex matrices, accentuate the difficulty to study these agents in a forensic purpose. Complementary to specific detection of targeted compounds, untargeted approaches can provide further information without a priori in sourcing fields. Organophosphorous compounds can be used as nerve agents, and can be produced by more or less complex synthesis routes. In this work, we present an original approach for source determination of synthetic chemicals based on the specificity of synthesis by-products, impurities, and other compounds. Using untargeted fingerprints, crude chlorpyrifos, a phosphorous pesticide, from different syntheses was employed as a first use-case using metabolomics-based trace discovery strategies [4]. Considering different reactants and protocols, seven synthetic routes and corresponding crude reaction mixtures were investigated. Samples were randomly analyzed with a minimal sample preparation to keep as much chemical information as possible. Analyses were performed on a Waters Synapt G2-Si Q-ToF high resolution mass spectrometer coupled to an Acquity I Class liquid chromatography system. Electrospray ionization parameters were optimized using several commercial synthetic intermediates of chlorpyrifos. After untargeted analysis of the crude materials using optimized analytical conditions, data were extracted, aligned and processed using the collaborative portal workflow4metabolomics (XCMS). Statistical analyses highlighted a set of significant features discriminating each synthetic pathway. MS/MS analyses were then conducted for unambiguous identification of the various by-products, intermediates, unreacted precursors or impurities allowing to reveal the synthetic route used. This workflow would be used to the characterization of discriminating compounds in future unknown samples.