Other Applications of Molecular MS

Biomolecules of all types can be analyzed by MS. The MW and seqnence of bases in nncleo-tides can be determined by MALDl-TOF-MS or by MS-MS. This allows the comparison of normal and mutated genes, for example. Analysis of nucleotides is important in medicine, agricnltnre. 

In organic and inorganic chemistry, MS can be used to identify reaction products and byproducts. Impurities at concentrations as low as parts per quadrillion can be detected MS is widely used for this purpose. In inorganic chemistry, with special inlet techniques, the elemental composition of materials as diverse as crystals and semiconductors can be determined. Reaction kinetics and ion-molecule reactions can be studied using MS. 

Polymers are routinely characterized by MS, with MALDI now being the most common form of sampling and ionization of polymeric materials, using MALDI-TOF-MS or MALDI-FTMS. Synthetic polymers actually have a distribution of chain lengths and so have a distribution of MWs. Polymer MWs are reported as the average MW (the center of the MW distribution). The average mass of polymers can be determined more accurately by MS than by the more conunonly anployed method of gel permeation chromatography (Section 13.4). 

The major limitation to the use of MS is that compounds must be volatile or must be able to be put into the gas phase without decomposing. A variety of ionization sources have been developed to handle materials that are volatile, semivolatile, nonvolatile, or thermally labile, as described in Chapters 9 and 13. For compounds that are not volatile, chemical derivatization to a more volatile form can be performed to make them suitable for MS or GC-MS, as described in Chapter 12. Carboxylic acids can be converted to the corresponding volatile methyl esters, for example trimethylsilane is another common derivatizing agent used to make volatile ether derivatives. 

Certain isomers cannot be distinguished by MS alone. Some isomers, such as the PCBs and PBDE isomers discussed in Section 10.3.5, may be able to be separated by chromatography prior to analysis by MS. 

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