Determining Mass Spectral Resolution

There are two major drawbacks to ISS concerning quantitative analysis. First, it has very low spectral resolution. Thus it is very difficult either to identify or resolve many common adjacent elements, such as Al/SI, K/Ca, and Cu/Zn. If the elements of interest are sufficiendy high in mass, this can be partially controlled by using a probe gas with a higher atomic mass, such as Ne or Ar. Second, ISS has an inherendy high spectral background which often makes it difficult to determine... 

Both compounds were non-fluorescent. Compound KM-1 was similar to PMs in the absorption maximum (A.max 488 nm) but not in the spectral shape, whereas KM-2 was similar to PMs in the spectral shape but not in the absorption maximum at 515 nm (Fig. 9.10). The chemical structures of KM-1 and KM-2 have been determined by high-resolution mass spectrometry and NMR spectrometry (Fig. 9.11 Stojanovic, 1995). 

Smith [83] classified large sets of hydrocarbon oil infrared spectral data by computer into correlation sets for individual classes of compounds. The correlation sets were then used to determine the class to which an unknown compound belongs from its mass spectral parameters. A correlation set is constructed by use of an ion-source summation, in which a low resolution mass spectrum is expressed as a set of numbers representing the contribution to the total ionisation of each of 14 ion series. The technique is particularly valuable in the examination of results from coupled gas chromatography-mass spectrometry of complex organic mixtures. 

Mass spectral (MS) determinations were performed on a Kratos MS 80 high-resolution mass spectrometer as described previously (3,13). 

Structure determination of the diterpenoid alkaloids (C20) has been a challenging task because of the diverse skeleta of these alkaloids. During the period ( 1962-1972), many of the structures were determined by X-ray crystal structure determination. The development of high resolution NMR and Mass spectral instruments has facilitated the structure elucidation and determination of the stereochemistry of the diterpenoid alkaloids. The structures of more than 240 naturally occurring diterpenoid alkaloids have been determined in the past twenty five years making use of, 3C NMR studies. 

NM R experiments (ID and 2D, homonuclear and heteronuclear) are the preeminent techniques for the determination of molecular structures. However, careful application and analysis of mass spectral data can provide sufficient information to postulate tentative structures. In this respect, the application of tandem MS experiments, sometimes in conjunction with selective derivatization of the unknown compound, can be very informative about the stmcture. The high-resolution mass spectral data are critical to the support of NMR-deduced stmctures by providing molecular formulae for unknowns. 

If high-resolution mass spectral data are available, the molecular formula can be determined directly. If the molecular ion had an exact mass of 88.0580, the molecular formula of X is C4H8O2 (exact mass = 88.0524) rather than C5H12O (exact mass = 88.0888) or C3H4O3 (exact mass = 88.0160). 

As mentioned above, mass spectral interpretation will be greatly aided if high mass accuracy data at high mass resolution are available to determine the elemental formula of the unknown and its fragments. Also there is increasing use of gas-phase ion/molecule reactions that can be exploited for class and functional group identification.141... 

Mass spectral studies play an important role in structure determination in this field. One of the major advantages is that only minute amounts of substrate are required for spectral measurement. Under high resolution conditions the compound s molecular weight can be determined with great accuracy tables are available for translation of this... 

The chemical structure of baogongteng A (1), a new myotic agent from Erycibe obtusifolia, has been determined. High-resolution mass-spectral data indicated the presence of a 3,6-disubstituted tropane skeleton. Infrared and and n.m.r. data indicated the presence of secondary amine, secondary hydroxyl, and acetoxy functions, and the location of the latter group at C-6 was based on comparison of n.m.r. chemical shifts with those of 6B-acetoxy-3a-tropanol. The hydroxyl group was assigned to the 23-position from the n.m.r. spectrum of the N-methylated alkaloid. 

Gibson and co-workers (69, 101-103) used the preceding apparatus to study gas evolution from geochemical and lunar soil samples. All the calculations of mass spectral data were made by a dedicated minicomputer system. Smith and Johnson (104, 105) described a multipurpose apparatus that permitted the determination of the TG, DTA, EGD. and MS curves to oil-shale research problems. Chang and Mead (106) described a TG-gas chromatograph-high-resolution mass spectrometer system and its application to the degradation of polymers. 

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