Suspect screening is useful when looking for one or more suspected compounds with known structures in a sample, but reference standards are unavailable or dont exist. In this case, user-built databases containing information such as mass accuracy, retention time, isotopic patterns, and other structure information for the suspected compounds are consulted, filtered, and compared against the results of high-resolution mass spectrometry analyses using SRM or full scans. The structure of the suspected compounds are then elucidated based on that information, ideally confirmed with authentic reference standards. Compared to targeted screening, the initial work performed in suspect screening is largely qualitative, with more quantitative work to potentially follow in a more targeted approach. Aside from being able to analyze for more compounds, an additional benefit of this approach is that retrospective analysis, even years later, is enabled without reanalyzing the sample. A downside to the suspect approach is the complexity involved, including not only with data analysis (e.g., using in silico' fragmentation software) but also carefully developing suspect screening lists and choosing databases.