The test sets of spectra considered in this study were taken from newer editions of the NIST and SWGDRUG MS libraries to ensure that the spectra were not contained in the reference libraries used in the SS-HM and iHS-HM. This means that the query spectra were analyzed and deemed acceptable for inclusion in high quality libraries. It is unclear how well the molecular mass prediction methods outlined in this paper will translate to data that has been obtained in less-thanideal circumstances. That said, it is always recommended that the query spectrum of an analyte be of high quality for any mass spectral library search-based procedure, whether traditional library searching or molecular mass prediction.