Mass spectrum libraries

Mass spectra obtained by El are highly reproducible on different instrumentation and over the time. This allows mass spectra libraries to be built in which an unknown mass spectrum can be searched by using an algorithm. Indeed, a lot of El mass spectra libraries containing hundreds of thousands of mass spectra, such as the NIST/EPA/NIH... 

Weinmann, W. Stoertzel, M. Vogt, S. Svohoda, M. Schreiher, A. Tuning Compounds for ESFin-Source ColUsion-Induced Dissociation and Mass Spectra Library Searching. J. Mass Spectrom. 2001,36,1013-1023. 

Muller, C., Schafer, P., Stortzel, M., Vogt, S., and Weinmann, W. (2002). Ion suppression effects in liquid chromatography-electrospray-ionization transport-region collision induced dissociation mass spectrometry with different serum extraction methods for systematic toxicological analysis with mass spectra libraries. /. Chromatogr. B 773, 47— 52. 

Chemical Analysis of Extracts. The extracts were analyzed by capillary column GC-MS for OCs, TAAPs, and PAHs (see the list on page 313). The GC-MS parameters used at the two laboratories are shown in Table II. The identification and quantitation were all done by using automatic routines based on a mass spectra library created from authentic standards of the selected compounds. Compounds were located by searching the reconstructed ion chromatogram for each library entry within a narrow retention time window relative to the internal standard (anthracene-dio or phenanthrene-dio). Quantitation was achieved by comparison of characteristic ion areas in the field samples with ion areas of the internal standard. These ion areas were normalized by response factors established by comparison of ion ratios of a standard mixture of all 66 analytes at a concentration of 2.5 ng//zL. 

Particle beam is especially useful in identifying unknown compounds, despite its limitations with respect to the quantification and its lack of sensitivity at trace levels (51). Particle beam-MS is generally carried out in the positive El, because EI-MS provides very reproducible mass spectra, and a wide variety of mass spectra libraries, containing up to 130,000 entries, are available for fast identification. Chemical ionization with positive (PCI) or negative (NCI) ion de-... 

Every organic chemical has a mass spectrum, which is a combination of ions with different masses and different intensities (abundances). To identify a compound, its mass spectrum is compared to the mass spectra of standards, analyzed under the same instrument settings, and to the EPA/National Institute for Standards and Technology (NIST) mass spectra library. The EPA/NIST library is stored in the database of the computer that operates the instrument. A comparison to the library spectra is possible only if there is consistency in the compound spectra generated by different GC/MS systems at hundreds of environmental laboratories. To achieve such consistency, the EPA methods for GC/MS analysis include the mass... 

Lew authors described antidepressant analysis in alternative specimens, such as hair or oral fluid. LC-CID-MS and MS/MS mass spectra libraries for identification of several drugs were employed by Muller et al. [32] for the detection of maprotiline, citalopram, and their desmethyl metabolites in authentic hair specimens extracted ions chromatograms were employed for subsequent antidepressant quantification. Also Klys et al. [33] applied LC-MS/MS to the analysis of blood, urine, and hair specimens in a fatal case due to clomipramine overdose in combination with alcohol. Blood clomipramine and norclomipramine concentrations explained the fatal outcome, and hair analysis confirmed that the deceased was on clomipramine treatment for, at least, 12 months prior to his death. With regard to oral fluid analysis, de Castro et al. [34] developed and validated a... 

W. Weinmann, M. Stoertzel, S. Vogt, M. Svoboda, A. Schreiber, Tuning compounds for ESI-in-source CID and mass spectra library searching, J. Mass Spectrom., 36 (2001) 1013. 

The separation of the silylated pyrolysate was done on a methyl silicone with 5% phenyl silicone chromatographic column, 60 m long, 0.32 mm i.d., 0.25 p film thickness. Some of the peaks in these chromatograms were identified. However, a significant number of peaks remained unidentified or only tentatively identified. Most peak identifications were done based only on the mass spectra library search (see Section 5.3). 

Figure 7.4.1. Starch pyrolysate at 59(f C and separated on a Carbowax column. Peak identification (by mass spectra library search) is indicated in Table 7,4.1.

These cumulative spectra provide information for polymer identification and can generate some structural hints. The search can be done on the special library or on regular mass spectra libraries (e.g. NIST 2002 or Wiley 7). For the cumulative spectrum of polyethylene pyrolysate, the regular mass spectra library indicates a long chain alkene and for poly(ethylene glycol) indicates bis(2-ethoxyethyl) ether, pointing to the dominant structure in the pyrolysate. However, the use of cumulative spectra is very limited in practice. 

Figure 6.7.6. Mass spectrum of dimethyl 2-methoxycarbonyl-4-methylenepentane-1,5-dioate MW =230 available in Wiley4 commercial mass spectra library.

Muller, C. Schafer, R Stortzel,M. Vogt, S. Weinmann, W. Ion Suppression Effects in Liquid Chromatography-Electrospray-Ionisation Transport-Region Collision Induced Dissociation Mass Spectrometry with Different Serum Extraction Methods for Systematic Toxicological Analysis with Mass Spectra Libraries, J. Chromatogr. B Anal. Technol. Biomed. Life Sci. 773(1), 47-52 (2002). 

To perform sample preparation by solid-phase extraction using a sufficiently large cartridge allows us to concentrate the sample 1000-fold and to perform MS analysis operating in SCAN mode in order to use the mass spectra libraries for compound identification. 

Dr. Ehrenstorfer GmbH in Augsburg, Germany has been supplying analytical standards for many years and they have produced a mass spectra library of over 1450 spectra of pesticides and their metaboHtes, PGBs, PAHs explosives and other environmentally important compounds [11]. 

Diaz, R., M. Ibanez, J. V. Sancho, and F. Hernandez. 2010. Building an empirical mass spectra library for screening of organic pollutants by UFIPLC-QTOF MS. Rapid Commun. Mass Spectrom. under revision. 

The huge amount of data generated by HRMS analyzers makes necessary the development of appropriate deconvolution software and accurate mass spectra libraries to improve identification of target and imtargeted compoimds. 

Theoretical mass spectra libraries, based on the molecular formula database, can be built which facilitate increasing the number of compounds that can be searched. These libraries use accurate mass measurements and isotopic pattern information for identification (Di az et al. 2012). Home-made empirical libraries can also be used, but these normally include much fewer compounds due to the need to inject... 

With the introduction of the reproducible chemical ionization into ion trap mass spectrometers, the first commercial Cl library with over 300 pesticides was produced by Finnigan Corp. in 1992. The introduction of substructure libraries (MS/MS product ion spectra) and accurate mass spectra libraries is currently ongoing (NIST). The commercially available libraries are divided into general extensive collections and special task-related collections with a narrow range of applications. 

The particle beam interface is very good for qualitative work because the 70 eV spectra contain a significant amount of structural information and can be searched against conventional mass spectra libraries. However, in the full scan mode the sensitivity is restricted to the low nanogram levels. 

The Library List window at the top right of Figure 8.5 allows the user to select the mass spectra libraries to be searched. The Min Pre-Search Hits window fixes the minimum number of spectra that will be selected at the end of the pre-research phase (see above). Increasing this value expands the length of the research (a small limitation based on the speed of modem computers) but reduces the risks of nnissing a solution if it exists. 

---