Spectrometry spectral interpretation

Maximum benefit from Gas Chromatography and Mass Spectrometry will be obtained if the user is aware of the information contained in the book. That is, Part I should be read to gain a practical understanding of GC/MS technology. In Part II, the reader will discover the nature of the material contained in each chapter. GC conditions for separating specific compounds are found under the appropriate chapter headings. The compounds for each GC separation are listed in order of elution, but more important, conditions that are likely to separate similar compound types are shown. Part II also contains information on derivatization, as well as on mass spectral interpretation for derivatized and underivatized compounds. Part III, combined with information from a library search, provides a list of ion masses and neutral losses for interpreting unknown compounds. The appendices in Part IV contain a wealth of information of value to the practice of GC and MS. 

Mass spectrometry is used to identify unknown compounds by means of their fragmentation pattern after electron impact. This pattern provides structural information. Mixtures of compounds must be separated by chromatography beforehand, e.g. gas chromatography/mass spectrometry (GC-MS) because fragments of different compounds may be superposed, thus making spectral interpretation complicated or impossible. To obtain complementary information about complex mixtures as a whole, it may be advantageous to have only one peak for each compound that corresponds to its molecular mass ([M]+). Even for thermally labile, nonvolatile compounds, this can be achieved by so-called soft desorption/ionisation techniques that evaporate and ionise the analytes without fragmentation, e.g. matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS). 

There is no one-and-only approach to the wide field of mass spectrometry. At least, it can be concluded from the preceding pages that it is necessary to learn about the ways of sample introduction, generation of ions, their mass analysis and their detection as well as about registration and presentation of mass spectra. The still missing issue is not inherent to a mass spectrometer, but of key importance for the successful application of mass spectrometry. This is mass spectral interpretation. All these items are correlated to each other in many ways and contribute to what we call mass spectrometry (Fig. 1.4). 

Bayliss, M. A., Antler, M., McGibbon, G., and Lashin, V. (2007). Rapid Metabolite Identification Using Advanced Algorithms for Mass Spectral Interpretation. In Proceedings of the 55th ASMS Conference on Mass Spectrometry and Allied Topics. ASMS, Indianapolis, IN. 

Compound identifications were made by combined gas chromatography-mass spectrometry (GC-MS) based on relative retention times and mass spectral interpretations. The instrument used was a Finnigan 5100 computerized GC-MS system equipped with a 50 m x 0.32 mm i.d. fused silica capillary coated with CP Sil 8 CB (0.25 jim film thickness). Helium was used as carrier gas and the temperature program was as follows 110°C (2 min)- 3°C/min - 320°C. 

Most small peptides derived from protein sources contain a variety of polar and non-polar amino acids and as such are more difficult to handle. Nevertheless appreciation of the problems and considered chemical manipulation have allowed their MS elucidation [177-184] although a practical limit of about six amino acids in the peptide is reached before degradative procedures become advisable. An important step before sequencing a peptide by mass spectrometry is whenever possible to obtain the amino acid content by hydrolysis and conventional column chromatographic analysis. This assists in the selection of any chemical pretreatment and with the spectral interpretation. A variety of small peptides has been identified by a combination of methods and include 5 - 0X0 - L - prolyl - L - histadyl - L - prolinamide (2-pyrollidone-5-carboxylyl-... 

Hofstadler, S.A. Bakhtiar, R. Smith, R.D. Electrospray ionization mass spectrometry. 1. Instrumentation and spectral interpretation. J. Chem. Educ., 73, A82 (1996). 

Spectral Identiflcation of Metabolites and F . Interpretation of the results of mass spectrometry of semduramicin sodium and its metabolites was facilitated by comparison with the fast atom bombardment mass spectral (FAB-MS) analysis of maduramicin sodium and other iono-phores (23), the thermospray liquid chromatography/tandem mass spectrometry of maduramicin and its metabolites (14, 24), and the extensive review of the mass spectrometry of polyether antibiotics (25). In this way, mass spectral interpretations were formulated for semduramicin and... 

This edition has been completely rewritten, revised, and expanded. To achieve this, the previous approach of having each chapter be self-contained has been abandoned repetition has been reduced to a minimum so that more topics could be covered in more detail. The topics of chromatography and mass spectrometry have been greatly expanded when compared with the 5th edition to better reflect the predominance of chromatography and mass spectrometry instmmentation in modem laboratories. The equally important topic of NMR has been refocused on FTNMR and expanded to included and 2D NMR spectral interpretation. 

Detection, characterization, and identification of metabolites require multiple mass spectrometry experiments such as full scan LC/MS and LC/MS/MS. The process becomes very time consuming, particularly when a large number of metabolites are formed. The interpretation of LC/MS/MS data is very laborious and inefficient, and can be a rate-limiting step in the metabolite identification process. Therefore, new approaches to data acquisition that would minimize the need for multiple experiments, and data processing tools that would simplify mass spectral interpretation, are highly desired. 

For a more complete description, as well as ease of comprehension of the broad field of mass spectrometry including mass spectral interpretation, please refer to Ref. (77). A somewhat oversimplified schematic of a quadrupole MSD is shown in Fig. 4.37 and depicts the trajectory of a resonant ion that makes it through the four rods of the quadrupole and a nonresonant ion that does not. The effluent from a WCOT can be fitted in... 

These spectra allowed the characterisation of the additives by spectral library search and/or spectral interpretation. The usefulness of the spray-jet interface system for the coupling of size exclusion chromatography(SEC) and FTIR spectrometry was examined on the basis of the analysis of a PS standard mixture. Representative IR spectra of the SEC effluent indicated that the SEC-FTIR system could be used for the determination of compositional changes across the polymer MWD. 25 refs. 

Adams and Sedgwick C33 reported a reciprocal correlation between predictive ability for mass spectral classifications and the molecular complexity (characterized by the number of characters in the Uiswesser notation). Crawford and Morrison C603 stated for their computerized mass spectral interpretation system which includes some pattern recognition techniques "Its capability is of the same order as that of an undergraduate student who had completed a course of 16 lectures on organic mass spectrometry". 

Expert systems have been extensively applied in many branches of analytical science, and in a number of noteworthy cases (generally involving molecular structure elucidation from spectroscopic data) such applications have led to the development of the technology. In addition to organic, molecular spectroscopy automated spectral interpretation systems have also been developed for X-ray diffraction. X-ray fluorescence, and, as advisors for instrument optimization, for atomic absorption spectrometry. 

Online separation technique is not necessary for production of end group fingerprint spectra. This provides the advantage of simplicity and no need of compromising ESI condition and separation conditions. However, the presence of any low mass impurities in the polymer sample causes complications in spectral interpretation. Low mass impurities can be removed by offline separation by LC prior to tandem mass spectrometry (MS/MS) experiments. 

Because of its highly discriminative capability, Fourier transform infrared (FTIR) spectrometry is valuable for identification of unknown compounds by comparison of sample spectra to reference spectra or by spectral interpretation (Somsen et al., 1995). IR spectra have been obtained on eluted samples or directly on TLC plates. About 5 pg is usually required for the elution method, which involves scraping of the zone and elution from the layer material onto an IR-transparent substance such as KBr (Issaq, 1983). Spectra can be measured directly on TLC plates by diffuse reflectance Fourier transform (DRIFT) IR spectrometry (Zuber et al, 1984). For in situ DRIFT-IR spectrometry, which requires 1-10 pg of compound, solvents must be removed from the layer and spectra corrected... 

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