The observed limitations with regard to the chemical space for which accurate predictions are possible hinders application for many parent environmental chemicals which are enriched with halogens and/or S compared to endogenous analytes. In addition, the spectral prediction for many metabolites is likely to also be poor due to their higher proportion of P and rotatable bonds . However, previous investigations to predict spectra of endogenous analytes rarely included P (Table ). Simply tuning simulation parameters may not significantly enhance predictions, instead, it is proposed that accurate calculation of potential energy surfaces or the incorporation of excited-state MD may enhance accuracy within the semi-empirical framework . Recently, Wang et al. incorporated excited states into the MD steps of EI spectra using the binary-encounter-Bethe (BEB) model, achieving higher accuracy, although limitations still exist, particularly for non-organic molecules.