Mass spectrometry differential sensitivity

Mass spectrometry — It has excellent sensitivity but low throughput and is semiquantitative. The ICAT (isotope-coded affinity tag) labeling method for proteins enables differential display analyses using mass spectrometry (Griffin and Abersold, 2001). This may be... 

The on-line coupling of CE with electrospray ionization mass spectrometry (CE-ESI-MS) allows high separation efficiency together with high sensitivity and selectivity as well as molecular structural information. A CE-UV-ESI-MS method was developed for the analysis of hoscyamine, scopolamine, and other tropane derivatives [131]. The differentiation of hyoscyamine from littorine, commonly encountered in plant material, was demonstrated using in-source collision-induced dissociation. The developed method was applied to the analysis of these alkaloids in Belladonna leaf extract and in Datura Candida x D. awreahairy root extract. Recently, CE coupled with electrochemiluminescence detection has been used for the determination of atropine and scopolamine in Flos daturae [132]. 

Although it has been demonstrated that quinine and quinidine only can be separated on packed columns with polar stationary phases , Furner et al. 6 used a non-polar stationary phase - in combination with mass spectrometry - to achieve a gas chromatographic differentiation of the two isomers. When the mass spectrometer was operated in the seleced ion monitoring (SIM) mode, 5 ng or less of quinine was detectable. That is, quinine and quinidine could be differentiated based upon selected ions. The possibility for developing a highly sensitive quantitative assay was discussed. 

The complex solution and surface chemistry involved in a typical sample can lead to large apparent differential sensitivities between quite similar compounds. Nevertheless, the FAB ion source has proven to be a valuable method for the recording of mass spectra of compounds that were previously considered to be intractable by mass spectrometry because they were too ionic and too involatile. Without doubt the californium-252 source is the leader in terms of bombardment technique with respect to high molecular weight determination and this situation is likely to persist if we take into account the large amounts of energy available in this sputter process. 

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