The effect of cone voltage on electrospray mass spectra of the bisquaternary ammonium salt decamethoxinum

Abstract

The effect of cone voltage (CV) variation on the mass spectral pattern of the bisquaternary ammonium salt decamethoxinum in the electrospray ionization (ESI) mode was studied. The advantage of decamethoxinum as a test compound in ESI mass spectrometry lies in the production of two types of precursor ions, i.e. the doubly charged organic dication Cat 2R and its singly charged cluster with a Cl S counterion, Cat Á Cl R . This makes it possible to monitor the fragmentation patterns of these ions under identical experimental conditions. Pronounced qualitative and quantitative changes in the ESI mass spectra were observed upon a gradual increase of the CV. The model compound decamethoxinum allowed us to reveal the extreme situation, in which the mass spectra at a CV below and over approximately 100 V look quite different, in that they contain different product ions of Cat 2R and Cat Á Cl R . While this effect may be much less pronounced for other classes of organic compounds, it should be properly taken into account for the adequate description of fragmentation pathways of bisquaternary ammonium compounds with ESI. Comparison of ESI, FAB-SIMS and MALDI mass spectra of decamethoxinum shows that taking into account CV effects also permits us to gain information on energy deposition into ions generated with the different ionization techniques. 10,[37][38][39][40][41][42] It is believed that the CV effect is due to an in-source collision-induced dissociation (CID) (up-front CID) process. The initially sprayed charged species can undergo collisions with the residual or bath gas on their path between the nozzle and the skimmer, and the change of the ion velocity caused by CV variation affects their kinetic energy and, consequently, their collision energy. 18The possibility of controlling the charge state of the ions, the desolvation process and the degree of fragmentation of the ions by CV variation offers the prospect of many useful applications of this technique, mainly in studies of supramolecular noncovalent complexes. [25][26][27][28][29][30][31][32][33][34][35][36] For example, a method was suggested for evaluating the stability of chemotherapeutic non-intercalating drugs binding to DNA on the basis of monitoring DNA-drug complex decomposition upon CV increase, which correlates with the thermal decomposition of the complex. 25,26 CV adjustment is also of critical importance in probing the structures of surfactant micelles generated under ESI conditions. 30,31 In-source CID is used along with collision-cell tandem mass spectrometric (MS/MS) CID in studies of protein structures. [19][20][21][32][33][34][35][36] Comparison of in-cell CID and in-source CID 32 permits us to obtain more comprehensive information on the molecular structures of analytes. A method, denoted as energydependent ESI mass spectrometry (EDESI-MS), employing CV variation, has been reported for fragmentation studies of metalloorganic compounds.

Validation of Direct Analysis Real Time source/Time-of-Flight Mass Spectrometry for organophosphate quantitation on wafer surface

“…Finally, under these two different temperatures an important decrease is observed when the sampling cone voltage reaches 50 V. The same behavior was previously observed [20] for other compounds adsorbed on other surfaces. It was ascribed to the higher energy levels inducing less effective focusing of the ions under high levels of the sampling cone voltage [20]. The different optimum values obtained for the two different temperatures shows the interdependence between these two experimental factors.…”

Is there a ‘matrix suppression effect’ under fast‐atom bombardment liquid secondary ion mass spectrometry of ionic surfactants in glycerol?

“…These surface activity features are important for another ionization technique which permits us to study solutions, namely, electrospray ionization (ESI). In particular, high quality ESI spectra of decamethoxinum21 and aethonium were obtained only when pure methanol or ethanol was used as solvent. Using water solvent or a water/methanol mixture (often used in protein studies) resulted either in unstable ion production or in no spectra at all, obviously because of micelle formation in the liquid (confirmed by the slight opalescence of these solutions).…”

“…It was decided to compare positive and negative ion LSIMS spectra of cationic and anionic surfactants and their binary mixtures. We selected two bisquaternary ammonium salts, decamethoxinum and aethonium, well studied in our previous works,18–21 as cationic surfactants and the widely used sodium dodecyl sulfate (SDS) as an anionic surfactant. The data obtained were interpreted by applying the notions of surface and colloid chemistry concerning the interfacial EDL.…”

Variable Electrospray Ionization and Matrix-Assisted Laser Desorption/ Ionization Mass Spectra of the Bisquaternary Ammonium Salt Ethonium

“…The extent of so-called dequaternization leading to the transformation of quaternary groups to tertiary amines, which is similar to the main thermal degradation pathway of quaternary compounds, can be considered as a measure of the thermal excitation acquired by the BQAC under given conditions. Under ESI conditions the mass spectral pattern of a BQAC depends strongly on such a parameter of the electrospray ion source as the cone voltage (CV) (called also nozzle-skimmer potential or orifice potential) [28,31]. Usually, at low CV values the salt dication Cat 2+ dominates, while at higher CV it is destroyed and replaced by the dication-counterion cluster Cat 2+ •Anion - [26][27][28]31].…”

“…In this context, the aim of the present work was to systematize the experimental conditions-dependent features of electrospray (ESI) and matrix-assisted laser desorption/ionization (MALDI) mass spectra of ethonium. A brief summary of basic information on the peculiarities of mass spectra of BQACs, obtained earlier by various techniques [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] and relevant to the subject of the present investigation, is as follows. The main types of primary ions expected in the soft ionization mass spectra of BQACs are the salt dication Cat 2+ and its cluster with the salt anion Cat 2+ •Anion -.…”