![]() This website has many screenshots ( SciFinder1, SciFinder2, ChemSpider) that illustrate these approaches with many examples. are used to narrow the list to one structure. ![]() Other ancillary information such as mass spectral fragments in EI or CID spectra isotopic abundances, UV spectra types of ion adducts CI data number of exchangeable protons etc. The candidate structures from the CAS Registry or ChemSpider searches are prioritized by either the number of associated references or key words. We had originally used this approach to search the TSCA database or our Eastman Chemical plant material listing. We define them as “spectra-less” databases because they contain no computer-searchable mass spectral data. This data is used to search very large databases such as the CAS Registry or ChemSpider via web interfaces. “Spectra-Less” Database Searching: If the NIST search is not successful, then accurate mass data is used to obtain a molecular formula (MF), a monoisotopic mass, or an average molecular weight. The NIST search interfaces easily with a wide variety of manufacturers’ data processing and structural drawing programs: We use the NIST and Wiley commercial databases, but there are many other specialty databases that others might find useful. MoNA EI and Tandem Libraries in NIST format The MoNA “crowd-sourced” libraries in NIST EI and Tandem formats are found at the following link: ![]() We employ both purchased, in-house, and “crowd-sourced” libraries. The computer EI searches normally work better than CID ones, but the latter are still very useful. I have developed two free “webinar” series courses that detail the use of the NIST search with EI and tandem libraries for the identification of unknowns: NIST Search of EI and CID Spectra: The initial step in our process utilizes computer searches of EI (GC-MS) or CID (LC-MS) spectra against reference databases using the NIST MS search. The “spectraless” ones are discussed at the bottom of this post. The approach uses either NIST libraries or “spectraless” databases such as the CAS Registry or ChemSpider. The article originated from work presented at Pittcon in 2012. This process is described in detail in the February 2013 copy of LCGC, “MS-The Practical Art.” The article is entitled: “Identifying “Known Unknowns” in Commercial Products by Mass Spectrometry.” A copy with associated ads is shown below: The process is shown in the following simplified flowchart: We define “known unknowns” as non-targeted species which are known in the chemical literature or mass spectrometry reference databases, but unknown to the investigator. Introduction: In the last 34 years, we have developed a systematic process for the identification of “known unknowns” by GC-MS and LC-MS in commercial products. Note: Details on other subjects are found in “My Topics” tab under sailboat picture above or on the sidebar links to the right. Systematic Process for the Identification of “Known Unknowns” in Commercial Products by GC-MS and LC-MS : “Approaches for Identifying New Psychoactive Substances (NPS)” at 2023 Current Trends in Seized Drugs Analysis Symposiumġ1/01/22: Training for Wiley KnowItAll New EI Mass Spec Capabilities : FREE Courses for GC-MS and LC-MS Identifications Using NIST Search SoftwareĤ/27/23: NIST2023 Libraries and Software Available in Early June
0 Comments
Leave a Reply. |