Collision-Induced Signal Enhancement:  A Method To Increase Product Ion Intensities in MS/MS and MSⁿ Experiments

Abstract

Collision-induced signal enhancement (CISE), a new technique to enhance the MSn capabilities of the quadrupole ion trap, is demonstrated. CISE is based on the chemistry, i.e., the dissociation pathways, of the analyte examined. Polysaccharides up to hexamers are used to demonstrate the capabilities of CISE to enhance signal in two distinct functional modes. Mode 1 CISE is designed to enhance the signal of an ion desired for MSn analysis. Mode 2 CISE is designed to enhance structurally significant product ions in an MS/MS spectrum. Two different approaches can be utilized to effect the two functional modes of CISE. Both approaches use conventional resonant excitation techniques to effect dissociation, which is performed nonanalytically, i.e., without isolation of the ions to be dissociated. The two approaches are (1) single-frequency resonance excitation, and (2) broad-band wave form resonant excitation. Experimental results for Mode 1 CISE analysis demonstrate up to a 17.3-fold signal increase for the single-frequency approach and 5.3-fold using broad-band excitation. Mode 2 CISE analysis shows up to a 16.3-fold increase in signal strength with single-frequency excitation and 3.3-fold using broad-band excitation.

Collision-induced signal enhancement (CISE): The use of boundary activation to effect non-resonant CISE

“…The signal enhancements obtainable with this technique are very similar to those previously obtained using broadband resonant excitation CISE and typically a factor of 2-3 less than those observed with single frequency resonance excitation [1]. The ability to obtain such enhancement values using BA-CISE is somewhat unanticipated considering that the best MS/MS efficiency seen for boundary activation in Figure 3 is not even 50%, whereas using the single frequency resonant excitation the MS/MS efficiency previously measured for lithium cationized ␣-1 3 6 linked disaccharides and ␤ 3 4 linked disaccharides is 89% [20].…”

“…Polysaccharide dissociation pathways have been thoroughly examined by MS/MS and MS n analysis [16 -20]. Because the dissociation pathways and ion formation propensities of the three polysaccharides studied here have been described elsewhere and summarized in the previous work describing CISE, [1] only a brief summary will be provided here. Using Domon-Costello nomenclature [17], C x type ions are of similar structure to intact polysaccharides and dissociate to all the product ions expected of an intact polysaccharide with x residues.…”

“…The viability of CISE as an effective technique depends on the existence of dissociation pathways from ions present in a product ion spectrum to the next generation parent ion. CISE through the use of single frequency and broadband waveform resonance excitation has been reported previously [1]. Another method to increase the kinetic energy of ions and effect dissociation to perform CISE in a quadrupole ion trap is explored in this work.…”

“…a z is a parameter of the Mathieu second-order differential equations of motions of ions in a quadrupole ion trap. It is defined in equation 1 a z ϭ Ϫ16eU m(r 0 2 ϩ 2z 0 2 )⍀ 2 (1) where (m) is the mass of the ion, (e) is the electronic charge, (r 0 ) and (z 0 ) are the radial and axial ion trap dimensions, respectively, (⍀) is the ac radial frequency of the trapping voltage, and (U) is the dc voltage amplitude. Since r o , z o , and ⍀ are constants of a given quadrupole ion trap, for a given mass/charge ratio, the a z value is only dependent upon the dc voltage.…”

“…Polysaccharides are used here, as in the previous CISE work [1], to demonstrate BA-CISE because there are many relevant dissociation pathways. CISE can certainly be utilized with systems other than polysaccharides.…”