Nozzle-skimmer dissociation

Example Even a moderate voltage drop between nozzle and skimmer can cause the elimination of weakly bonded substituents such as CO2 in case of carbon dioxide-protected deprotonated A-heterocycles. In particular, SnMej-substituted anions such as 2-(trismethylstannyl)pyrrole-7V-carbamate exhibit strong variations in the [A-C02]7A ratio of up to a factor of 30 preventing the detection of A at slightly elevated voltages (Fig. 12.9) [80]. 

For NSD it is not required to have a true nozzle-skimmer arrangement. Instead, a potential drop of 20-100 V across a suitable pressure region of any ESI interface design suffices to induce this sort of CID. The Bruker Apollo II ESI source, for example, features a dual ion funnel setup with the first ion funnel in the rough vacuum of the supersonic expansion plume ( 3-4 mbar) and the second ion funnel prior to an RF-only hexapole used to alternatively guide or accumulate ions. 

Here NSD or in-source CID as it is termed by the manufacturer, is achieved by shifting the DC potentials as to have the largest voltage drop at the entrance into the second ion funnel where a pressure of 0.1 mbar is suitable for low-energy CID (Fig. 12.10). 

Funnel 1.1MHz, 200Vpp Hexapole -4.8MHz, SOOVpp 

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H. Zhai, X. Han, K. Breuker, F.W. McLafferty, Consecutive ion activation for top down MS Improved protein sequencing by nozzle-skimmer dissociation. Anal. Chem., 77 (2005) 5777. 

ESI-Infrared Multiphoton Dissociation IRMPD of ESI-generated ions can also provide sequence information. By combining the data from the nozzle-skimmer dissociation and IRMPD experiments, nearly complete sequence coverage for larger oligonucleotides can be obtained [48]. These two dissociation techniques yield complementary sequence ions. For example, IRMPD primarily produces w- and (a — B )-type sequence ions, whereas the nozzle-skimmer dissociation generates b-, c-, and [Pg.467]

Figure 13.10. Nozzle-skimmer dissociation spectrum of an 8-mer oligonucleotide 5 -(CG AGCTCG)-3. (Reproduced from ref. 48 by permission of the American Chemical Society, Washington, DC, copyright 1994.)...

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